摘要:

Journal of Materials Chemistry Scientific Advisory Editor Professor Martin R. Bryce Department of Chemistry University of Durham South Road Durham DHl 3LE, UK Associate Editor Professor Jean Etourneau ICMCB Avenue du Docteur Schweitzer 33600 Pessac France Editorial board Allan E. Underhill (Chairman) Bangor Peter G. Bruce St. Andrews Martin R. Bryce Durham Jean Etourneau Bordeaux Managing Editor Janet L. Dean Deputy Editor Zoe G. Lewin Assistant Editor Graham F. McCann Editorial Secretary Miss D. J. Halls Wendy R. Flavell UMIST John W. Goodby Hull Klaus Praefcke Berlin Brian J. Tighe Aston International advisory editorial board K. Bechgaard Rim, Denmark J. Y. Becker Beer-Sheva, Israel A. J. Bruce Murray Hill, USA E.Chiellini Pisa, Italy D. Coates Poole, UK P. Day London, UK D. A. Dunmur Shefield, UK B. Dunn Los Angeles, USA W. J. Feast Durham, UK R. H. Friend Cambridge, UK A. Fukuda Tokyo, Japan D. Gatteschi Florence, Italy P. Hodge Munchester, UK Information for authors The Royal Society of Chemistry welcomes submission of manuscripts intended for publication in two forms, Articles and Materials Chemistry Communications. These should describe original work of high quality dealing with the synthesis, structures, properties and applications of materials, particularly those associated with advanced technology. Full papers contain original scientific work that has not been published previously. However, work that has appeared in print in a short form such as a Materials Chemistry Communication is normally acceptable.Four copies of Articles including a top copy with figures etc. should be sent to the Managing Editor at the Cambridge address. Journal of Materials Chemistry (ISSN 0959-9428) is published monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry, Turpin Distribution Services Ltd., Blackhorse Road, Letchworth, Herts SG6 lHN, UK. NB Turpin Distribution Services Ltd., distributors, is wholly owned by The Royal Society of Chemistry. 1996 Annual subscription rate EEA (incl. UK) E519.00, USA $934.00, Rest of World E532.00.Customers A. B. Holmes Cambridge, UK H. Inokuchi Okazaki, Japan W. Jeitschko Munster, Germany 0.Kahn Bordeaux, France J. Livage Paris, France R. McCullough Pittsburgh, USA J. S. Miller Salt Lake City, USA K. Miillen Mainz, Germany L. Niinisto Espoo, Finland M. Nygren Stockholm, Sweden Y. W. Park Seoul, Korea N. Plat6 Moscow, Russia Materials Chemistry Communications contain novel scientific work in short form and of such importance that rapid publication is warranted. The total length is normally restricted to two printed A4 pages. However, special consideration will be given to communications with a large amount of essential diagrammatic information. Submission of a Materials Chemistry Communication can be made either to the Managing Editor at the Cambridge address, or via a member of the International Advisory Editorial Board.In the latter case, the top copy of the manuscript including any figures etc., together with the name of the person to whom the Communication is being submitted, should be sent simultaneously to the Managing Editor at the Cambridge address. All authors submitting work for publication are should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003. USA POSTMASTER: send address changes to Journal of Materials Chemistry, Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003.Second Class postage paid at Jamaica, NY 11431. All other dispatches outside the UK by Bulk Airmail within Europe, Accelerated Surface Post outside Europe. PRINTED IN THE UK. Editorial Production Coordinator Stephanie Shah Technical Editors Carole J. Nerney Alan J. Holder Graphics Designer Ms C. Taylor-Reid Anthony R. West Aberdeen John D. Wright Canterbury Janet L. Dean (Secretary) M. Prato Trieste, Italy C. N. R. Rao Bangalore, India B. Raveau Caen, France T. Rojo Bilbao, Spain J. Rouxel Nantes, France A. Simon Stuttgart, Germany M. A. Subramanian Wilmington, USA S. Takahashi Osaka, Japan J. 0.Thomas Uppsala, Sweden M.Vallet-Regi Madrid, Spain D. E. W. Vaughan Annandale, USA Y. Yamashita Okazaki, Japan required to sign an exclusive copyright licence. All submissions should be accompanied by a completed form (a blank for photocopying is reproduced at the end of the Information for Authors in Issue l), without which publication cannot proceed. A completed graphical abstract template should also accompany each submission. Full details of the form of manuscripts for Articles and Materials Chemistry Communications, conditions for acceptance etc. are given in Issue 1 of Journal of Materials Chemistry published in January of each year, on the world wide web (htpp://chemistry.rsc.org/rsc/) or may be obtained from the Managing Editor. There is no page charge for papers published in Journal of Materials Chemistry. Fifty reprints are supplied free of charge. Janet L. Dean, Managing Editor Tel.: Cambridge (01223) 420066 E-Mail (INTERNET): DEANJ@RSC.ORG Fax: (01223) 420247 Advertisement sales: Tel. $44 (0)171-287 3091; Fax +44 (0)171-494 1134 0The Royal Society of Chemistry, 1996. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mecharical, photographic, recording, or otherwise, without the prior permission of the publishers.

ISSN:0959-9428    

DOI:10.1039/JM99606FX009

出版商:RSC    

年代:1996

数据来源: RSC

ISSN:0959-9428    

DOI:10.1039/JM99606BX011

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

ISSN 0959-9428 JMACEP(6) 677-903 (1996) Synthesis, structures, properties and applications of materials, particularly those associated with advanced technology Feature Article 677 Thin film formulations of substituted pht haloc y anines 6 Michael J. Cook 0Y ($If assembled monolayers) Articles 691 Preparation of ultrafine particle multilayers using the Langmuir-Blodgett technique Tadao Nakaya, Yu-Jun Li and Kazunori Shibata 699 Preparation and characterisation of conductive Langmuir-Blodgett films of a tetrabutylammonium-Ni(dmit), complex Leonid M. Goldenberg, Christopher Pearson, Martin R. Bryce and Michael C. Petty 705 Laser photolytic studies of sensitizers for negative photoresists: 2,7-diazidofluorene in poly(methy1 methacrylate) films Tsutomu Yamamoto, Hiroshi Miyasaka, Akira Itaya, Minoru Toriumi and Takumi Ueno i 711 Novel optically transparent polyesters containing a high density of second-order non-linear optically active chromophores Nobukatsu Nemoto, Fusae Miyata, Yu Nagase, Jiro Abe, Makoto Hasegawa and Yasuo Shirai 719 Chemical modification of monolithic poly (styrenedivinylbenzene) PolyHIPE@ materials - - Neil R.Cameron, David C. Sherrington, Isao Ando and Hiromichi Kurosu X = -SO,H, -NO,, -Br 727 Copper ion binding to N-phenylphthalamic acid studied by 13Cnuclear magnetic resonance and electron paramagnetic resonance: model O A interaction of polyamic acid with copper Toshifumi Hiraoki, Noriyuki Kinjo, Kunio Miyazaki, Osamu Miura and Akihiro Tsutsumi 733 Mesogenic properties of novel enamino ketone ligands and their copper (n) complexes Jadwiga Szydlowska, Wieslaw Pyzuk, Adam Krowczynski and Ildar Bikchantaev 739 Structural variation of liquid crystalline trioxadecalins X2.Volkmar Vill, Hanns-Walter Tunger and Markus von Minden 'oY = COO-phenyl, -CH~-CH~-,-CEC- ~OCnH* + 1 " 747 Synthesis and mesogenic properties of 3,6-disubstituted cyclohex-2-en-1-ones Roger Brettle, David A.Dunmur, Louise D. Farrand and Charles M. Marson 753 Stability of the antiferroelectric phase in dimeric liquid crystals having two chiral centres with CF, or CH, groups; evaluation of conformational and electric interactions Yoshi-Ichi Suzuki, Tadaaki Isozaki, Shigeharu Hashimoto, Tetsuo Kusumoto, Tamejiro Hiyama, Yoichi Takanishi, Hideo Takezoe and Atsuo Fukuda 761 Oriented cadmium oxide thin solid films Metodija Z. Najdoski, Ivan S.Grozdanov and Biljana Minceva-Sukarova 765 Morphology control of thin LiCoO, films fabricated using the electrostatic spray deposition (ESD) technique Chunhua Chen, Erik M.Kelder, Paul J. J. M. van der Put and Joop Schoonman 773 Synthesis, properties and performances of electrodeposited bismuth telluride films Pierre Magri, Clotilde Boulanger and Jean-Marie Lecuire 781 Oxidation of alkaline-earth-metal sulfide powders and thin films Janos Madarasz, Tuula Leskela, Janne Rautanen and Lauri Niinisto R Zoo0 loo0 Ei,Te, 2Billl + 3Te'" + 18e- $0 ~ -2BiIII + 3Tew + 18e- -loo0 -5M) -250 0 250 503 753 EImV (vs.SCE) -130 120 ill0 100 80 80 ?O ... 111 789 LiSb(edta)(H,O): a convenient precursor to LiSbS2 and LiSbO, Bertrand Marrot, Chantal Brouca-Cabarrecq and Alain Mosset 795 Preparation and electrical conductivity of neod ymium-europium oxide fluorides Masayuki Takashima, Susumu Yonezawa, Kiyoshi Horita, Kouichi Ohwaki and Hiroshi Takahashi 801 Structure refinement, magnetic susceptibility, electrical conductivity and europium-151 Mossbauer spectroscopy of EuNiIn, Rainer Pottgen, Ralf Mullmann, Bernd D. Mosel and Hellmut Eckert 807 Magnetic properties of ternary chromium sulfides, V,Cr, -3,(0 <x < 1.0) Anthony V.Powell and Sascha Oestreich 815 Fabrication of La, -,Sr,CoO,-, thin layers on porous supports by a polymeric sol-gel process Chunhua Chen, Henny J. M. Bouwmeester, Henk Kruidhof, Johan E. ten Elshof and Anthony J. Burggraaf 821 Additive-assisted pressureless sintering of carbothermal /l"-sialon: an X-ray and solid-state MAS NMR study Kenneth J. D. MacKenzie and Richard H. Meinhold Nd 0 Eu F @o La :O 5641nm :I I227nm 1 VCr,S4 41,. . . . . , , . , , . m 2Y) 3m' Irn 7?K *'At NMR 29SlNMR 25M9NMRn 1 1v 833 Thermal reactions of alkali-leached A C aluminosilicates studied by XRD and solid-state "Al, 29Siand 23Na MAS NMR 10 mln, 1300 OC mrnln.Kenneth J. D. MacKenzie, Richard H. Meinhold, Akshoy K. Chakravorty and M. H. Dafadar 843 A 23Na NMR study of hydrous layered silicates Na,O (4-22)Si02 (5-1O)H,O Graham G. Almond, Robin K. Harris, makatite kanemite Kevin R. Franklin and Peter Graham magadiite oc tasilica te kenyaite 849 Organometallic cation-exchanged phyllosilicates: variable-temperature 57FeMossbauer spectroscopic and related studies of the adsorption of dimethylaminomethylferroceneon clays and pillared clays Christopher Breen, John S. Brooks, 18.8 AI Susan Forder and Julian C. E. Hamer 861 Intercalation of n-alkylamines into misfit layer sulfides Lourdes Hernan, Pedro Lavela, Julian Morales, Luis Sanchez and Jose L. Tirado 867 Optical and EPR spectroscopic studies of silver clusters in Ag,Na-Y zeolite by y-irradiation E.Gachard, J. Belloni and M. A. Subramanian 87 1 Rheology and microstructure of aqueous layered 1 double hydroxide dispersions v) Louise Albiston, Kevin R. Franklin, Elizabeth Lee and J. Bas A. F. Smeulders m &p 01 40 > 0 01 0 loo0 2000 3000 4000 5000 tIs V 879 Preparation, characterization and surface structure of coprecipitated high-area Sr,TiO,+,(O<x< 1) powders Jose Manuel Gallardo Amores, Vicente Sanchez Escribano, Marco Daturi and Guido Busca Ti02 anatase SrTi03 887 Photoluminescence study of (CaO), -*( ZnO), &= 200 nrn powder solids in air Loukia A. Loukatzikou, Antonios T.Sdoukos and Philip J. Pomonis hlnm 895 Study of the order-disorder transition in yttria- 7-----7stabilised zirconia by neutron diffraction 70 Iain R. Gibson and John T. S. Irvine 075 O.'m 0.85 0,'W 0.95 1 00 1.05 d-spacnq/A Materials Chemistry Communication 899 Investigation of the stability of the hexagonal- cubic boron nitride prism interface Jorg Widany, Thomas Frauenheim and h-BN C-BNWalter R. L. Lambrecht I 903 Book Reviews: Raoul Cervini; Martin R. Bryce i Cumulative Author Index ... 111 Conference Diary Note: Where an asterisk appears against the name of one or more authors, it is included with the authors' approval to indicate that correspondence may be addressed to this person. COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles. For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK. Tel: +44 (0)171-437 8656, Fax: +44 (0)171-287 9798, Telecom Gold 84: BUR210, Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society's Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge. vi

ISSN:0959-9428    

DOI:10.1039/JM99606FP025

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Cumulative Author Index 1996 Abe J., 711 Albiston L., 871 Alcan tara-Rodriguez M., 247 Ali F., 261 Ah-Adib Z., 15 Allen J. L., 165 Almond G. G., 843 Alonso P. J., 533 Al-Raihani H., 495 Ando I., 719 Andrews S. R., 539 Antonietta Massucci M., 645 Arai H., 455 Arai K., 11 Aranda M. A. G., 639 Chen J., 465 Chen X., 1, 615 Chippindale A. M., 611 Chisholm M. S., 527 Choi J. U., 365 Chung D. D. L., 469 Chung H., 365 Clarkson G. J., 315 Clearfield A., 639 Cole-Hamilton D. J., 507 Cook M. J., 149, 677 Cooke S., 1 Cowley A. R., 611 Crayston J. A., 187 Dafadar M. H., 833 D’Andrea G., 585 Daolio S., 567 Green D. A., 449 Grobelna B., 579 Grobet P., 239 Grozdanov I. S., 761 GunBer W., 547 Guo L-H., 369 Guzman G., 505 Hahn J. H., 365 Hall S. B., 183 Hamada D., 69 Hamer J. C. E., 849 Hamerton I., 305, 311 Hamet J-F., 165 Hamilton D.G., 23 Harding J. H., 653 Harkema S., 357 Harris R. K., 843 Knowles J. A,, 89 Kochubey D. I., 207 Koehler K., 579 Koto K., 459 Kremer R. K., 635 Kristof J., 567 Krowczynski A,, 733 Kruidhof H., 815 Kudnig J., 547 Kuroda K., 69 Kurosu H., 719 Kusumoto T., 753 Klonkowski A. M., 579 Labes M. M., 1 Lai S-W., 469 Lambrecht W. R. L., 899 Lavela P., 41, 861 Nagase Y., 711 Naito H., 33 Najdoski M. Z., 761 Nakano H., 117 Nakaya T., 691 Neat R. J., 49 Nemoto N., 71 1 Newport R. J., 337, 449 Nickel K. G., 595 Nieminen M., 27 Nii H., 97 Niinisto L., 27, 781 Noma N., 117 Nortier P., 653 Nygren M., 97 O’Brien P., 343 Oestreich S., 807 Arriortua M. I., 421 Ashwell G. J., Attfield J. P., 57 Bahloul-Hourlier D., 595 23, 131, 137 Daturi M., 879 Davies A., 49 Davies T.W., 73 Davis F., 15 Harrison W. T. A., 81 Hasegawa M., 711 Hasegawa N., 605 Hashimoto S., 753 Lecuire J-M., 773 Lee C. K., 331 Lee E., 109, 871 Lee G. R., 187 Ogawa K., 143 Ohwaki K., 795 Ohyama T., 11 Olbrich F., 547 Bahra G. S., 23 Barberis G. E., 421 Bardosova M., 375 Barrans Y., 5 Davis S. J., 479 Dawson D. H., 409 de Lacy Costello B. P. J., 289 Hayashi H., 459 Heald R. C., 311 Hernan L., 37, 861 Herrera-Urbina R., 573 Le Flem G., 381 Lequan M., 5, 555 Lequan R. M., 5, 555 Lerner M. M., 103 Olivera-Pastor P., 247 Olivier-Fourcade J., 41 Omenat A., 349 Oriakhi C. O., 103 Barrel1 K. J., 323 Delmas C., 193 Hersans R., 149 Leskela M., 161 Otterstedt J-E., 213 Barton J. M., 305 Barzoukas M., 555 Bassoul P., 5 Bast1 Z., 155 Battisti A.De., 567 Battle P. D., 201, 395 Baur W. H., 271 de Souza D. P. F., de Souza M. F., 233 Dirken P. J., 337 Domingues-Rodrigues Dommisse R., 559 Dotze M., 547 233 A,, 207 Hervieu M., 165, 175 Hiraoki T., 727 Hitch T. J. A. R., 285 Hiyama T., 753 Hobson R. J., 49 Hodge P., 15, 375, 527 Hoffmann R-D., 429 Leskela T., 781 Lezama L. M., 421 Li Y-J., 691 Lin C. L., 1 Lin J., 265 Lindroos S., 161 Liu S., 305 Pac C., 143 Pagura C., 567 Parent C., 381 Park J. W., 365 Partridge R. D., 183 Pearson C., 699 Pedrini C., 381 Bay B. H., 331 Behrens U., 547 Belloni J., 867 Dragone R., 403 Dunmur D. A., 747 Durand B., 495 Holloway A., 629 Holloway J., 221 Holmes P. A., 539 Livage J., 505 Llavona R., 415 Lorriaux-Rubbens A., 385 Peeters K., 239 Pelloquin D., 175 Peng B-X., 559 Berry F.J., 221 Beteille F., 505 Dussack L. L., 81 Duvauchelle N., 573 Honeybourne C. L., 285,289, 323 277, Loukatzikou L. A,, 887 Lowendahl L., 213 Peng Z-H., 559 Pereira-Ramos J-P., 37 Bieniok A,, 271 Bikchantaev I., 733 Eadon D., Eckert H., 221 801 Horita K., 795 Howlin B. J., 305, 311 Lynch D. E., Machida M., 23 69, 455 Perrin M-A., 653 Pertierra P., 415 Blin J. L., 385 Bomben A,, 15 Bornholdt K., 271 Eguchi K., 455 Elhsissen K. T., 573 Ellert 0. G., 207 Huang K-S., 123 Hudson M. J., 49, 89 Humberstone P., 315 MacKenzie K. J. D., Macklin W. J., 49 833 821, Petrunenko I. A., 207 Petty M. C., 699 Picard C., 619 Boulanger C., 773 Boutinaud P., 381 Bouwmeester H. J. M., 815 Enoki T., 119 Enomoto M., 119 Etter the late M.C., 123 Ihanus J., 161 Iimura N., 671 Ikemoto I., 501 Madarasz J., 781 Magri P., 773 Maksimov Y. V., 207 Piccirillo C., 567 Pickett N. L., 507 Pizarro J. L., 421 Boyle D. S., 227 Branger C., 555 Bravic G., 5 Breen C., 253, 849 Brendel U., 271 Eustace P., 527 Evans P., 289, 295 Ewen R. J., 289 Farcy J., 37 Farr I. V., 103 Imae I., 117 Ingram-Jones V. J., 73 Inman D., 495 Inoue H., 455 Inui S., 671 Mann B. E., 253 Marcos M., 349, 533 Marrot B., 789 Marson C. M., 747 Martinez E. S., 547 Pola J., 155 Pomonis P. J., 887 Poojary D. M., 639 Pottgen R., 63, 429, 635, 801 Brettle R., 747 Farrand L. D., 747 Irvine J. T. S., 895 Martinez J. I., 533 Powell A. V., 807 Britton D., 123 Brooks J. S., 849 Brouca-Cabarrecq C., 789 Brown C.R., 23 Bruque S., 639 Bryce M. R., 699, 903 Bukhtenko 0.V., 207 Ferragina C., 645 Flint S. D., 629 Forder S., 849 Fort A., 555 Foster D. F., 507 Franke U., 547 Franklin K. R., 109, 843, Isozaki T., 753 Itaya A., 705 Iwane H., 671 Iyoda M., 501 Jackson P. D., 137 Jacobson A. J., 81 James M., 57 Marucci A., 403 Marugan M. M., 667 Matijevii- E., 443 Matsuyama H., 501 Mattei G., 403 McKeown N. B., 315 McLendon G., 369 Prellier W., 165 Pyzuk W., 733 Qian M., 435. Qun L., 559 Ranjan R., 131 Rao K. J., 391 Rasheed R. K., 277 Burggraaf A. J., Busca G., 879 815 Frauenheim T., 871 899 Janes R., 183 Jansson K., 97, 213 McMurdo J., 149 Meinhold R. H., 821, 833 Rasika Abeysinghe J., 155 Ratcliffe N. M., 289, 295, Bush T. S., 395 Fukuda A., 671, 753 Jarmo Koivusaari K., 449 Mercey B., 165 301 Bushnell-Wye G., Byrn S.R., 123 Cabeza A., 639 Cabrera S., 175 337, 449 Gachard E., 867 Gallardo Amores J. M., Ganguli M., 391 Gao Y., 369 879 Jefferies G., 131, 137 Jimtnez-L6pez E. R- C. A., 247 Jones J. R., 305 Merle-Mejean T., 595 Michel C., 175 Minami T., 459 Minceva-Sukarova B., 761 Rauhala E., 27 Rautanen J., 781 Raveau B., 165, 175 Rawson J. O., 253 Caldes M. T., 175 Garcia J. R., 415 Judeinstein P., 511 Miura O., 727 Razafitrimo H., 369 Calleja R. D., 547 Cameron N. R., 719 Campbell S. A., 295 Campillos E., 349, 533 Campostrini R., 585 Carleer R., 559 Carroll S., 559 Garcia-Granda S., 415 Gay D. H., 653 Gazzoli D., 403 Geise H. J., 559 Gentle I. R., 137 George C. D., 131 Gerdanian P., 619 Jumas J-C., 41 Kaczorowski D., 429 Kagawa S., 97 Kanamura K., 33 Kanniainen T., 161 Katerski A., 377 Kaul A.R., 623 Miyachi K., 671 Miyasaka H., 705 Miyata F., 711 Miyazaki A., 119 Miyazaki K., 727 Moffat J. B., 459 Moine B., 381 Rigden J. S., 337, 449 Rodriguez J., 415 Rodriguez M. L., 415 Rodriguez-Castellon E., Rohl A. L., 653 Rojo T., 421 Russell D. A., 149 247 Carturan G., 585 Catlow C. R. A., 653 Gibson I. R., 895 Glenis S., 1 Kawaguchi K., 117 Kelder E. M., 765 Monk P. M. S., 183 Moon J. H., 365 Saadoune I., 193 Saito K., 501 Ceccato R., 585 Cerrini R., 903 Chakravorty A. K., 833 Chane-Ching K., 5 Charters R. B., 131 Gogotsi Y. G., 595 Goldenberg L. M., 699 Gomi Y., 119 Goiii A., 421 Gorbenko 0. Y., 623 Kennard C. H.L., Khomenko G. E., Kikuchi K., 501 Kim J. H., 365 Kim S. B., 365 595 23, 137 Morales J., 37, 41, 861 Mori T., 501 Moriga T., 459 Morineau R., 505 Mosel B. D., 635, 801 Salvado M. A., 415 Salvador S., 73 Samoylenkov S. V., 623 Sanchez C., 511 Sanchez Escribano V., 879 Chassagneux F., 495 Chasseau D., 5 Chen C., 765, 815 Gore J. G., 201 Graboy I. E., 623 Graham P., 843 Kinjo N., 727 Kitazawa T., 119 Klar G., 547 Mosset A., 789 Mulley S., 661 Mullmann R., 635, 801 Sanchez L., 37, 861 Sanchis M. J., 547 Sanders G. M., 357 i Sano T., 605 Smith M. E., 261, 337 Takezoe H., 753 Tundo P., 15 Whitfield H. J., 261 Sasaki S., 501 Sayle D. C., 653 Schnelle W., 635 Schoonman J., 765 Schouten P. G., 357 Sdoukos A. T., 887 Segal N., 395 Serrano J.L., 349, 533 Sherrington D. C., 719 Shibata K., 691 Shinton S., 667 Shirai Y., 711 Shirota Y., 117 Shitara Y., 11 Silvert P-Y., 573 Singh N., 629 Sironi A., 661 Skjerlie K. P., 595 Slade R C. T., Smart L. E., 221 Smeulders J. B. A. F., Smith I. K., 539 Smith J. R., 295 73, 629 871 Smrcok L., 629 Soraru G. D., 585 Southern J. C., 73 Stefanis A. De., 661 Steuernagel S., 261 Stoev M., 377 Su Q., 265 Suarez M., 415 Subramanian M. A., 867 Subrt J., 155 Sudholter E. J. R., 357 Sugahara Y., 69 Sugiyama S., 459 Suzuki H., 501 Suzuki T., 671 Suzuki Y-i., 753 Szydlowska J., 733 Takahashi H., 795 Takahashi M., 119 Takanishi Y., 671, 753 Takashima M., 795 Takeda M., 119 Takehara Z-I., 33 Tamaura Y., 605 Tanaka M., 459 Tatam R. P., 131 Taylor R., 155 Teare G. C., 301 ten Elshof J.E., 815 Teraoka Y., 97 Teunis C. J., 357 Tirado J. L., Tomkinson J., 449 Tomlinson A. A. G., 645, Toriumi M., 705 Torncrona A., 213 Tran V. H., 429 Treacher K. E., 315 Tredgold R. H., 375 Tretyakov Y. D., 623 Trindade T., 343 Troc R., 429 Tsodikov M. V., 207 Tsuji M., 605 Tsutsumi A., 727 37, 41, 861 66 1 Tunega D., 629 Tunger H-W., 739 Uddin R., 527 Ueno T., 705 Vaidhyanathan B., 391 Valigi M., 403 Valli L., 15 van der Put P. J. J. M., 765 van de Velde G. M. H., 357 van Dijk M., 357 Vansant E. F., 239 Vaughey J. T., 81 Vente J. F., 395 Vijayakrishnan V., 573 Vill V., 739 Vogt T., 81 von Minden M., 739 Wallart F., 385 Walton R. I., 611 Wang S., 265 Warman J. M., 357 Watts J. F., 479 West A. R., 331 Widany J., 899 Widernik T., 579 Wignacourt J. P., 385 Williams D.E., 409 Williams G., 539, 667 Winfield J. M., 227 Woolley M., 375 Xu R., 465 Yamamoto T., 705 Yao J., 143 Yao T., 33 Yonehara H., 143 Yonezawa S., 795 Yoshino H., 501 Yue Y., 465 Zeng H. C., 435 Zhang B., 639 Zhang H., 265, 615 Zhang P., 615 Zhong Q., 443 Zimmer B., 547 Zhou X-F., 559 11 Conference Diary June 1996 International Conference on Intelligent Materials Lyon, France Mrs Claude Bernavon ICIM 96, Group d'Etudes de MBtallurgie Physique et de Physique de Materiaux, B5t. 502 -ler etage, Institut National des Sciences Appliques de Lyon, 20 avenue Albert Einstein, F 69621 Villeurbanne Cedex, France. E-mail: bernavon@insa.insa-1yon.fr;Tel: +33 72 43 83 85; Fax: +33 72 43 88 30. June 3-6 Dedicated Conference on Materials for Energy-Efficient Vehicles Florence, Italy The ISATA Secretariat, 42 Lloyd Park Avenue, Croydon CRO 5SB, UK.E-mail: 100270.12G3@COMPUSERVE.COM;Tel: +44 181 681 3069; Fax: +44 181 686 1490 June 3-7 4th World Surfactants Congress Barcelona, Spain J. Sanchez Leal, General Secretary, CESIO AEPSAT, Comite Espaiiol de la Detergencia (CED). -Jordi Girona, 18-26. 08034 Barcelona, Spain. E-mail: cesio96@cid.csic.es; Tel: (343) 204 02 12 -400 61 00; Fax: (343) 280 53 00 -204 59 04. June 8-13 Fundamental Aspects of Surface Science: Semiconductor Surfaces Blankenberge, Belgium Dr Josip Hendekovic, European Science Foundation, 1quai Lezay-MarnBsia, 67080 Strasbourg Cedex, France. E-mail: euresco@esf.c-strasbourg.fr; Tel: +33 88 76 71 35; Fax: +33 88 36 69 87.June 10-13 Science and Technology of Pigment Dispersion Luzern, Switzerland Dr A. V. Patsis, Director, Institute for Materials Science, State University of New York, New Paltz, NY 12561, USA. Tel: +914 255 0757; Fax: +914 255 0978. June 17-19 18th International Conference in Stabilization and Controlled Degradation of Polymers Luzern, Switzerland Dr A.V. Patsis, Director, Institute for Materials Science, State University of New York, New Paltz, NY 12561, USA. Tel: +914 255 0757; Fax: +914 255 0978. June 24-28 ILCC: 16th International Liquid Crystal Conference Kent, OH, USA 16th International Liquid Crystal Conference, Liquid Crystal Institute, Kent State University, P.O. Box 5190, Kent, OH 44242-0001, USA. E-mail: ILCClG@alice.kent.edu; Tel: +1 216 672 2654; Fax: +l 216 672 2796.June 24-28 1 lth Bratislava IUPAC International Conference on Polymers High Tatras Bratislava, Slovakia Dr Lyda Rychla, Polymer Institute, Slovak Academy of Sciences, Dubravska cesta, CS 842-36 Bratislava, Slovakia. E-mail: upolrych@savba.sk; Tel: 0042 7 37 34 48; Fax: 0042 7 37 59 23. June 26-28 TMS, 1996 38th Electronic Materials Conference The Minerals, Metals & Materials Society (TMS), 420 Coninionwealth Drive, Warrendale, PA 15086, USA E-mail: csc@tnis.org; Tel: 412-776-9000; Fax: 412-776-3770 July 1-5 22nd International Conference in Organic Coatings -Waterborne, High Solids, Powder Coatings Athens, Greece Dr A.V. Patsis, Director, Knstitute for Materials Science, State University of New York, New Paltz, NY 12561, USA.Tel: +914 155 0757; Fax: +914 255 0978. July 6-12 Solid State Chemistry '96 Bratislava, Slovak Republic SSCH '96, Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava, Slovak Republic July 7-12 XVIIth International Conference Organometallic Chemistry Brisbane, Australia XVIIth ICOMC Secretariat, Faculty of Science and Technology, Griffth University, Brisbane 4111, Australia. E-mail: ICOMC@sct.gu.edu.au; Tel: +61 (017 3875 7217; Fax: +G1 (017 3875 7656. July 8-10 ESOPS 12 -"12th European Symposium on Polymer Spectroscopy" Lyon, France Dr G. Lachenal, Universite Lyon 1,Laboratoire des Materiaux Plastiques, Bld du 11Novembre 69622 Villeurbanne, Cedex France. E-mail: lachenal@matplast.univ-1yonl.fr;Tel: +33 72 43 12 11; Fax: +33 72 43 12 49.July 28- International Conference on Science and Technology of Synthetic Metals August 2 Utah, USA Professor Z. Valy Vardeny, Secretary General, ICSM '96, Physics Department, 214 JFB, University of Utah, Salt Lake City, Utah 84112, USA E-mail: icsm96@mail.physics.utah.edu; Tel: +801 581 8372; Fax: +801 581 4801 July 29- Recent Advances in Polymer Synthesis August 2 York, UK Professor P. Hodge, Department of Chemistry, University of Manchester, Oxford Road, Manchester, UK M13 9PL. E-mail: Philip.Hodge@man.ac.uk; Tel: +44 (0) 161 275 4706; Fax: +44 (0) 161 275 4598. August 4-9 IUPAC MACRO SEOUL '96: 36th IUPAC International Symposium on Macromolecules Seoul, Korea Dr. Kwang Ung Kim, Secretariat of IUPAC MACRO SEOUL '96, Division of Polymers, Korea Institute of Science and Technology, P.O.Box 131, Cheongryang. Seoul 130-650, Korea. E-mail: iupac@kistmail.kist.re.kr; Tel: +82 2 957 6104; Fax: +82 2 957 6105. ... 111 August 4-9 The Tenth American Conference on Crystal Growth Colorado, USA Anthony L. Gentile, American Association for Crystal Growth, PO Box 3233,Thousand Oaks, CA 91359-0233USA Fax: 805 492 4062 August 28-31 10th Conference of the European Society of Biomechanics Leuven, Belgium Dr. J. Vander Sloten, Executive Secretary, 10th Conference of the European Society of Biomechanics, Katholieke Universiteit Leuven, Division of Biomechanics and Engineering Design, Celestijnenlaan 200A, B-3001 Heverlee, Belgium.E-mail: jos.vandersloten@mech.kuleuven.ac.be;Tel: +32 16 32 70 96; Fax: +32 16 29 27 16. September 1-6 XIth International Symposium on Organosilicon Chemistry Montpellier, France Professor R.J.P. Corriu, Laboratoire des Precurseurs Organonietalliques de Matkriaux, UMR CNRS 44,Universite de Montpellier 11, Place E. Bataillon, CC 007, F34095 Montpellier Cedex 5,France Fax: +67 14 38 88. September 1-6 ECME 96, Third European Conference on Molecular Electronics Leuven, Belgium Professor F.C. De Schryver, Department of Chemistry, K.U. Leuven, Celestijnenlaan 200F, B-3001Heverlee, Belgium. September 9-10 Molecular Modelling of Chemicals and Materials Amsterdam, The Netherlands Dr A.M. Brouwer, Laboratory of Organic Chemistry, Amsterdam Institute of Molecular Studies (AIMS), Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands.E-mail: mgms@chem.uva.nl; Fax: 31 (0)20 5255670; WWW page: http://krop.chem.uva.nl/mgms/ September 10-15 Reactivity in Organised Microstructures: Chemical Reactions and Physical Processes in Compartmentalized Systems Santiago de Conipostela, Spain Dr Josip Hendekovic, European Science Foundation, 1 quai Lezay-Mamesia, 67080 Strasbourg Cedex, France E-mail: euresco@esf.org; Tel: +33 88 76 71 35; Fax: +33 88 36 69 87 October 9-14 Physical Metallurgy: Interfacial Engineering in Materials Castelvecchio Pascoli, Italy Dr Josip Hendekovic, European Science Foundation, 1 quai Lezay-Marnesia, 67080Strasbourg Cedex, France. E-mail: euresco@esf.c-strasbourg.fr;Tel: +33 88 76 71 35; Fax: +33 88 36 69 87. October 13-18 ISLC '96: 15th International Semiconductor Laser Conference Haifa, Can Carniel, Israel IEEELEOS, 445 Hoes Lane, P.O.Box 1331,Piscataway, NJ 08855-1331,USA. Tel: +I 908 562 3898; Fax: +1 908 562 8434. October 27-12th International Congress on Advances in Non-Impact Printing Technologies November 1 San Antonio, TX, USA Conference Manager, IS&T, 7003 Kilworth Lane, Springfield, VA 22 151, USA. E-mail: imagesoc@us.net; Tel: +1 703 642 9090; Fax: +1 703 642 9094. November 16-23 IS&T/SID Fourth Color Imaging Conference: Color Science, Systems & Applications Scottsdale, AZ,USA Conference Manager, IS&T, 7003 Kilworth Lane, Springfield, VA 22151,USA. E-mail: imagesoc@us.net; Tel: +1 703 642 9090; Fax: +1 703 642 9094.1997 April 8 International Symposium on Applications of Magnetic Resonance in Materials Science Guildford, UK Professor G.A. Webb or Dr J.N. Hay, The Department of chemistry, University of Surrey, Guildford, GU2 5XH, UK Tel: +1483 300 800; Fax: +1483 259 514 May 26-28 EPDIC -5; 5th European Powder Diffraction Conference Parma, Italy Professor G. Artioli, Dipartimento di Scienze della Terra, Universita' di Milano, Via Botticelli 23,I-20133Milano, Italy E-mail: artioli@iummix.terra.unimi.it; Tel: +39 2 23698320; Fax: +39 2 70638681 July 14-18 The 3rd International Conference on Materials Chemistry University of Exeter, UK August 24-27 ZMPC '97 International Symposium on Zeolites and Microporous Crystals Tokyo, Japan Dr Takahashi Tatsumi, Secretary, ZMPC '97,Engineering Research Institute, Faculty of Engineering, The University of Tokyo, Yayoi, Tokyo 113,Japan.0 Denotes a new or amended entry this month. Entries in the Conference Diary are published free of charge. If you wish to include an announcement please send full details to: Journal of Materials Chemistry Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK, CB4 4WF. Tel: +44 1223 420066; Fax: +44 1223 426017. iv THE ROYAL SOCiETYOFCHEMISTRY CALL FOR PAPERS ORGANIC PROCESS RESEARCH AND DEVELOPMENT FA-A new journal from The Royal Society of Chemistry *& and the American Chemical Society Information Services Scientific Editor: Trevor Laird, Scientific Update (UK) Associate Editors: John F Arnett, Recombinant BioCatalysis, Inc (USA) Richard Pariza, C&P Associates (USA) The Royal Society of Chemistry and the American Chemical Society are pleased to announce the co-publication of Organic Process Research and Development.The premiere issue of this new bi-monthly research journal will be released in January 1997. Organic Process Research and Development will report on original work in the broad field of process chemistry encompassing aspects of organic chemistry, catalysis, analytical chemistry and chemical engineering, with a special focus on the design of chemical processes and their translation from laboratory, via pilot plant, to manufacture. The journal will cover R&D in the fine organic chemical and specialty chemical industries, including pharmaceuticals, electronics, agrochemicals, intermediates, flavours and fragrances, food additives, dyestuffs and photographic chemicals, and specialty polymers.Academic work in these areas will also be covered. The journal will conceptrate on the batchhemibatch chemical process industries, but also welcomes reports on R&D aimed at continuous processes. Submissions for Organic Process Research and Development are now being sought. We are particularly keen to receive papers in the following areas: 4 Organic process research 4 Organic process development 4 Scale-up issues 4 Related safety issues 4 New technologies 4 Environmental waste minimization and 4 Legislation and regulatory issues benign or green chemistry related to process R&D Submissions can be full research papers, reviews, notes, summaries of research (no experimental details necessary), technology reports, etc. The deadline for receipt of papers for possible inclusion in the inaugural issue is July 31st 1996. Interested authors should contact the editors to request a comprehensive Guide for Authors. Submissions may be forwarded to: Trevor Laird, Editor, Scientific Update Wyvern Cottage, High Street, Mayfield, East Sussex TN20 6AE, UK Tel. 44- 1435-873062 Fax. 44- 1435-872734 John F Arnett, Associate Editor, Richard Pariza, Associate Editor Recombinant BioCatalysis, Inc C& P Associates Elmwood Court 2,512 Elmwood Ave, Sharon Hill, 43323 Oakcrest Lane, North Zion, PA 19079-1005 USA IL 60099-941 3 USA Tel. 1-610-237-7515 Fax. 1-610-237-7565 Tel./Fax. 1-708-872-6925

ISSN:0959-9428    

DOI:10.1039/JM99606BP031

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

FEATURE ARTICLE Thin film formulations of substituted phthalocyanines Michael J. Cook School of Chemical Sciences, University of East AngEia, Norwich, UK NR4 7TJ Phthalocyanines are macrocyclic compounds which possess a variety of properties of potential importance in advanced technologies. The article considers the development of phthalocyanine derivatives for deposition as thin films by the Langmuir- Blodgett method, spin-coating and self-assembly. Important aspects in this area of research are the development of good quality films which contain a high and reproducible degree of molecular order and the deposition of films constructed with different types of molecular packing. Attention is drawn to the potential of purpose-designed non-uniformly substituted amphiphilic derivatives.A number of these exhibit liquid-crystal behaviour as the bulk material and this appears also to be manifested in some of the films. The potential of examples of the films as the detecting component in gas sensors is commented upon. Phthalocyanines (Pcs) possess some remarkable properties 24 23 which render them important commercial commodities. In particular, their intense blue/green colours and stability towards heat, acids and bases have ensured their extensive use as pigments and dyes. Furthermore, examples are used as catalysts for a number of industrial processes.' However, they 7 N I 25P22also possess some intriguing electrical, photophysical and redox properties and attention is being focused increasingly 77on exploiting them within an impressive range of advanced 3ebl-M-NDtechnologies, some potential, some already realised.2 Thus 16 there is extensive research into the applications of phthalocyan- ..ines in electr~photography,~ optical data storage sy~tems,~,~ 4 NyNyN 75 gas sensing device^,^,^ photovoltaic cells,' fuel cells,' and in electrochromic displays." Phthalocyanines are also recognized as having excellent potential in the photodynamic therapy of certain types of Many of these exciting develop- ments have been reviewed in articles elsewhere. Much of the fascination of research into phthalocyanines lies in the fact that the properties of the compounds, and these include the solid-state properties of various formulations as discussed later, can be tuned through relatively straightforward chemistry or fabrication procedures.On the chemical front, there is extraordinary potential for ringing the changes by varying the atom(s) at the centre of the macrocycle and by introducing substituents onto the ring system. Some 70 elements have been inserted into the central cavity. By far the most common derivatives are those of the 1:1 type, but small monovalent ions such as the proton and Li' form 2: 1 ion:macrocycle complexes and large ions, e.g. those of the rare-earth metals, form 1 :2 complexes. The introduction of substituents on the ring system raises the number of known or feasible derivatives almost beyond bounds. Axial ligation to a five- or six-coordinate atom at the centre of the macrocycle offers one option, but particular attention has been focused on the 16 available sites on the benzenoid rings.These sites fall into two categories, the so-called peripheral (2,3,9,10,16,17,23,24) and non-peripheral (1,4,8,11,15,18,22,25) positions (Fig. 1). Substituents are intro- duced either by substitution reactions on the preformed macro- cycle or, more commonly these days, through the use of appropriately substituted precursors, especially phthalonitrile derivative^.'^ Substituents provide the prime means of solubil- izing the ring system in either aqueous media or organic solvents and offer a useful way of tuning the wavelength of the visible region absorption band, the Q-band. Importantly, cer- tain substituents, in particular long aliphatic chains, can pro- mote discotic liquid-crystal beha~iour.'~ The most common 9 10 Fig.1 Phthalocyanine (Pc) ring system and part of the atom num- bering system. The 1,4,8,11,15,18,22,25 positions are referred to as the non-peripheral sites, the 2,3,9,10,16,17,23,24 positions as the peripheral sites. M can be H,H or one of up to ca. 70 elements of the periodic table. The article concentrates on derivatives of H,Pc and the metal(]]) derivatives, the MPcs. molecular packings adopted by such phthalocyanines in their mesophases are of the columnar type whereby the planar molecules stack like piles of coins. The columns are thought to be stabilised by interactions between the aromatic cores but are mobile once the side chains have 'melted'.Polymorphism of Unsubstituted Phthalocyanines A number of the applications of Pcs referred to above utilise the compounds in the solid state and this clearly drives much of the research into the properties of their solid-state formu- lations. Often, these properties are a function of the molecular packing for which there is a wealth of data, particularly for the unsubstituted ring system as its metal-free form, H,Pc, and when metallated with the common divalent metals to give the MPcs. Indeed, the patent literature refers to at least ten polymorphic forms of these derivatives, of which the a, /?and x-forms are perhaps the best known.I5 There are some ambi- guities concerning the extent of the differences between some of the other forms16 and further complications arise through subtle variants of the a-form.17 What is firmly established is J.Muter. Chem., 1996, 6(5), 677-689 677 that in sublimation experiments, the conditions and the sub- strate onto which the material is deposited can affect the packing significantly;" an unusual illustration of the impor- tance of conditions is provided by the growth of one of the newest polymorphs of CuPc during experiments in micro- gravity on the Orbiter space sh~ttle.'~-~' Crystals of the P-modification, normally regarded as the thermodynamically most stable form, can be grown by subli- mation at high temperature under an inert atm~sphere.~ X-Ray diffraction studies of single crystals of various transition-metal phthalocyanines reveal that the molecules stack in columns with the planes of the molecules tilted with respect to the column axe^.'^'^^ The direction of the tilt alternates from column to column to give the classic herring-bone arrangement found in a number of aromatic molecules.The normal of the plane of the phthalocyanine ring typically makes an angle of ca. 48" to the column axis. Films of the a-modification can be obtained by sublimation under high vacuum with collection on a substrate at room temperature. A single crystal X-ray diffraction study of the a-form2' of PtPc and electron diffraction studies of vacuum- condensed films of Cu, Co, Ni, Fe, Ni, Pt and the metal-free derivatives2' show that the tilt angle of the rings relative to the column axis is ca.26", much less than that in the @-form. Spectacular images have been obtained using high-resolution transmission electron microscopy, see for example the earlier review in this journal by Kobayashi and Isoda.22 These reveal the herring-bone structure but also show areas of disorder arising, for example, where the tilt in one column is in the wrong direction, i.e. in the same sense as those of the two adjacent columns. The a-form undergoes dimorphic change into the p-form, a transition facilitated by heat and exposure to solvent^.^^,^^ Grinding the @-form converts it into the a-f~rm,~' while neat milling of the a-form provides one of the methods for obtaining the x-polymorph.26 Each form gives rise to a characteristic absorption-band envelope in the visible region, known as the Q-band.The band structure is more complex than that observed in the solution phase where non-aggregated MPcs give rise to a single main band assigned to the doubly degenerate transition alu-eg. For metal-free complexes, the lower symmetry of the system lifts the degeneracy and the Q-band is split into two components. In the solid state, however, the spectra of MPcs and H2Pc are broadened through exciton coupling effects which also lead to shifts in the band positions. These are dependent upon molecu- lar packing.16 Thus, the p-form of metal-free phthalocyanine has a band envelope with the two most intense components centred at ca. 660 and 700 nm, while the a-form shows maxima at ca.600 nm and a lower intensity band at ca. 690 nm, A,,, varying somewhat according to the formulation and particle size.26,27 In contrast, the x-form has absorptions in the 560-660 nm and 780-800 nm regions.26 These differences are important with regard to the use of the compounds as pigments and, in higher technologies such as optical data storage and electrophotography, for choosing materials for matching laser or LED o~tput.~ Molecular packing also proves to be an important factor in conductiometric gas sensing applications. There have been many studies of the effects of doping sublimed films with both electron donor gases and, more especially, with oxidising gases such as NO,. Exposure of the films to the gases modulates the semiconductivity of the system.Donor-acceptor inter-actions are thought to facilitate charge-carrier generation, thus raising conductivity and providing a basis for an analytical probe. Comparative studies have shown that the electrical properties of films of different polymorphic forms differ for various metallated phthalocyanine~.~-~.~~ New Derivatives, New Formulations While substituents on the Pc ring can advantageously tune some of the system's electronic characteristics, they may also lead to new types of packing. This in turn expands the range and variety of properties of the macrocycle in the solid state. However, there is sometimes a price to pay in that the extraordinary thermal stability of the unsubstituted ring com- pounds may, in part, be sacrificed.Indeed, few substituted phthalocyanines have been satisfactorily sublimed without decomposition. On the other hand, the solubility in organic solvents conferred by substituents opens the way for the deposition of phthalocyanines as films by methods very differ- ent from sublimation. Three developments will be considered here, of which the main one is the application of the Langmuir- Blodgett (LB) technique, a methodology which has attracted much attention over the last 20 years and which was first applied satisfactorily to phthalocyanines in the early 1980s. The second development has been the exploitation of spin- coating methods. The procedure is much simpler and more convenient than the LB method, but there is less control over film thickness.The third development, one which gives ultra- thin films, is the newest and involves generating a self-assembled monolayer (SAM) chemically bonded to a substrate surface. Major challenges in these areas are the reproducible deposition of well ordered films and the design and develop- ment of derivatives which lead to different types of molecular packing. Langmuir-Blodgett Films The Langmuir-Blodgett procedure, recently reviewed in this journal,29 was devised in the 1930s and offers the possibility of constructing ultrathin films of organic molecules by transfer- ring molecular monolayers at an air-water interface onto a substrate, one monolayer at a time. The full experimental procedure is in two parts.In the first part, a small amount of the compound of interest, typically an amphiphilic material having both a hydrophilic headgroup and a hydrophobic tail, is transferred onto the surface of high-purity water as a dilute solution in an organic spreading solvent. The trough containing the water is fitted with a movable barrier and, once the solvent has evaporated, the barriers are gradually closed to reduce the surface area, A, available to the organic molecules. As the surface area is reduced, the molecules, originally well separated in the so-called two-dimensional gas phase, are compressed together, sometimes through a two-dimensional liquid or expanded state, until they form a close-packed monolayer.Ideally the monolayer is well ordered and this is frequently the case with amphiphilic molecules. Once the close-packed state is achieved, further compression causes a substantial increase in the surface pressure, n, until a point is reached where the molecular monolayer loses its structure and col- lapses. All these changes are monitored as a surface press- ure-area plot, the n-A isotherm. Release of the barriers at a compression point prior to collapse should lead to the reverse behaviour. Indeed, the profile of the n-A isotherm obtained during the compression-decompression cycle is an important indicator of the behaviour of the material as a monolayer. From a knowledge of the amount of material transferred onto the water surface and the area it occupies in the close-packed state, it is possible to calculate the mean area occupied per molecule, A,.This provides an indication of how the molecules are packed in the compressed monolayer. The second component of the LB experiment is the transfer of the molecular monolayer onto a solid substrate at a surface pressure corresponding to the close-packed state. The most common procedure is the vertical dipping method whereby the substrate, aligned normal to the water surface, is lowered through the monolayer which may then become attached to it. A second monolayer may then be deposited onto the first as the substrate is withdrawn from the water. This type of transfer is said to be Y-type and builds up a 'head-to-head', 'tail-to-tail' bilayer assembly.Alternative modes of deposition 678 J. Muter. Chem., 1996,6(5), 677-689 are X-type where transfer occurs only on the downstroke and Z-type with transfer only on the upstroke. During the transfer of material from the water surface onto the substrate, the barriers are closed to maintain a constant surface pressure. The second, less common, method of deposition is the hori- zontal lifting method. This involves lowering the horizontally aligned substrate such that it just touches the surface. A monolayer becomes attached and the substrate is lifted off. The first reported studies of phthalocyanines at an air-water interface appeared in the 1930s and were rather unpromising, functionalities. These include aryloxy particularly tetrac~mylphenoxy,~and alkoxy groups,41 and amide~.~~.~~Examples, illustrative rather than comprehensive, of compounds which have been deposited as films, and referred to in the text that follows, are gathered in Fig.2. Films of tri- and tetra-substituted phthalocyanines frequently give rise to a visible region absorption spectrum showing an intense band which is blue-shifted with respect to that observed in the solution-phase spectrum, see for example Fig. 3 which shows the spectrum of an LB film of asy-CuPc.4' There is The often also a weaker shoulder, more or less at the solution FePc and MgPc failing to form a stable m~nolayer.~~~~~ resurgence of interest in LB films of phthalocyanines com- menced in the early 1980s with results reported by Roberts' group at Durham.The group transferred Li,Pc, one of the more organic-solvent-soluble derivatives of the unsubstituted ring, onto the water surface where hydrolysis to H,Pc was expected. The resultant material was then deposited as an LB film.32 Secondly, and arguably more significantly, they initiated research into monolayer and deposition studies of organic- solvent-soluble substituted phthalocyanines and in particular the tris-N-isopropylaminomethylderivative, Pam-CuPc, and the tetra-tert-butyl derivatives, the ttb-MP~s,~',~~ the structures of which are shown in Fig. 2. The Durham group was among the first to identify the potential of the films as the active component of a conductiometric NO, gas sensor,33 and to show their use within electroluminescent diodes34 and a bistable Subsequently, there has been research on both unsubstituted and substituted phthalocyanines with the aim of producing films containing a good extent of molecular ordering and/or films for particular applications.Work on films of unsubstituted compounds has included annealing at 300°C a film of H,Pc phase A,,,. The spectrum is thus unlike those for the a-, /I-and x-polymorphs of the unsubstituted phthalocyanines dis- cussed earlier and signifies that a different type of molecular packing has been achieved. In particular, the appearance of the blue-shifted band can be attributed to exciton effects within a cofacial columnar structure.47 The extent of the blue shift reflects the length of the column.For example, LB films of AmPc1 give spectra in which A,,, varies between 608 and 614 nm depending upon deposition conditions; a theoretical treatment indicates that the 608 nm band corresponds to a stack containing 14.4 molecules.46 The spectra often show dichroism. That is to say, the absorbance differs when the films are interrogated with normal incident light polarized with the electric field vector, E, first orthogonal, I,and then parallel, 11, to the dipping direction, d. The transition moments for the two transitions giving rise to the Q-band are polarized in the plane of the ring and the observed transition will be strongest when the plane of the ring is perpendicular to the substrate and aligned with the direction of E.No dichroism is expected if the rings are lying with their planes parallel to the substrate surface. Nor will deposited under conditions used by Roberts' gro~p.~~*~~ The there be dichroism if the rings are randomly ordered within annealed film showed a visible band envelope similar to that of the a-form and exhibited electrochromism. In contrast, films of ZnPc gave spectra comparable to those of the a- and x- polymorphs, depending upon the surface pressure during dipping.38*39However, research into films of substituted deriva- tives of phthalocyanines has been much more intense. While there has been a continuing interest in various metallated ttb- Pcs, there has been much research into phthalocyanines tetra- substituted, one substituent per benzenoid ring, with other X x Commund Abbreviation X = -C&NHisoC3l+, X' = H pam-CuPc tbc-CuPc toc-CuPc tdc-cu Pc Fig.2 Examples of some tri- and tetra-substituted phthalocyanines referred to in the text. The abbreviations are based on those used in the literature. the film. Dichroism is therefore an indication of some degree of anisotropic order of molecules whose planes are tilted to the substrate. It is normally reported as the dichroic ratio, R, where R=Eld:Elld. R is sensitive to three factors. These are n 500 600 700 800A/ nm Fig. 3 Optical spectrum of asy-CuPc. The red-shifted band is for the material as a solution in chloroform. The remaining plots show the blue-shifted spectrum of the compound as a Y-type LB film and are measured with polarised light at various orientations to the substrate and the dipping direction.Reproduced by permission from ref. 40. J. Mater. Chem., 1996, 6(5), 677-689 679 the tilt angle of the rings relative to the substrate surface, the angle between the molecular axis parallel to the substrate and the dipping direction and, of course, the extent of uniformity of order. This makes interpretation difficult but, nevertheless, attempts have been made to quantify the precise orientation of the rings within the films through measurements of R at different angles of incidence of the interrogating beam.40,47 Qualitatively it can be stated that for cofacial columnar packing, R is greater than 1when the molecular planes are on average perpendicular to d, i.e.the columnar axes are, on average, aligned along d. Conversely, R is less than 1 when the column axes are on average aligned predominantly orthogonal to d. Both types of packing have been observed and are illustrated by results obtained for films of the tetrabutoxycar- bony1 derivative, tbc-CuPc, and its longer chain homologues, the octyloxy and decyloxy compounds toc-CuPc and tdc-CuPc (for structures see Fig. 2). LB films of tbc-CuPc give X-ray diffraction bands corresponding tp a repeat spacing, i.e. the width of the monolayer, of 18.8A consistent with the rings standing essentially perpendicular to the substrate surface.43 The dichroic ratio for the main absorption band at 618 nm is larger than unity.Its magnitude, which rather interestingly shows a dependency on the width of the substrate, is as high as 7.3: 1 for narrower slides of ca. 10-15 mm wide. On annealing at ca. 90°C the value of R rises further to ca. 16: 1. By contrast, films of toc-CuPc and tdc-CuPc show R of the order of 1:2.4 to 1 :2.6.44 A model to account for R being less than 1 postulates that columnar stacks are formed on the water surface. On compression they align with the stack axes parallel to the surface of the partially immersed substrate. These stacks are then transferred onto the substrate. While there is clearly good evidence for some degree of molecular order in films of a number of the tri- and tetra- substituted phthalocyanines, it is likely that the materials are mixtures of isomers and this is unlikely to promote optimum ordering.Accordingly, attention has also been given to octa- substituted compounds having a pair of identical substituents on either the two peripheral or non-peripheral positions of each benzenoid ring of the macrocycle. Such materials can be synthesised by unambiguous pathways to give single isomers. The first example to be investigated was peripherally substi- tuted octakis(dodecyloxymethyl)-CuPc.48The A, value was consistent with the molecules lying with the aromatic ring flat on the water surface with the aliphatic chains directed away. The compound underwent Y-type transfer and the film showed i,,,=615 nm with R= 1.9: 1.Peripherally substituted octaal- kyl Pcs also lie flat on the water surface and can be deposited by the horizontal lifting method.49 However, their non-periph- erally substituted analogues, R8 MPcs in Fig. 4, either fail to form a surface film or else give an A, value which is inconsistent with simple monolayer behavi~ur.'~ In a further contrast, non- peripherally substituted octaalkoxy Pcs, (RO)8MPcs in Fig. 4, form better monolayers which can undergo Z-or Y-type deposition depending upon the length of the aliphatic chain, the octapentyloxy derivatives forming the most even films.51 Finally, there has been an important body of work directed at peripherally substituted octaalkoxylated rings constrained within phthalocyaninato-polysiloxanepolymers.16 These mate- rials form linear, 'shish-kebab' polymers, the rod-like molecules depositing with the long axis preferentially parallel to the substrate surface.The films are characterised by exceptional blue shifts of the visible region band to ca. 555 nm.52 Monolayer and LB Deposition Behaviour of Amphiphilic Phthalocyanines While the octa-substituted phthalocyanine derivatives des- cribed above contain regions of differing hydrophilicity and hydrophobicity, their amphiphilic character does not approach 680 J. Muter. Chem., 1996, 6(5), 677-689 X = 0-Alkyl. Abbreviation (RO), MPc X =Alkyl. Abbreviation Rs MPc Fig. 4 Examples of non-peripherally octa-substituted phthalocyanines investigated for LB film deposition.The identifiers are those used in the text. M is H,H or a metal@) ion. that of the long-chain aliphatic carboxylic acids and alcohols which are among the classic materials examined for LB film deposition work. Since the mid-1980s the Norwich group, with important contributions from Richardson's group at Bristol and the DRA laboratories at Malvern, has investigated the synthesis and LB film-forming properties of a variety of purpose-designed phthalocyanine derivatives containing both hydrophilic and hydrophobic substituent groups. Fig. 5 shows R Q-R n = 1; (HO),(RO), MPc n = 1; (H0)& MPc n =3; (HO'),(RO), MPc n =3; (HO')& MPc n = various; (HO)R7 MPc. R and R' may be the same or different. Fig. 5 Examples of amphiphilic octa-substituted phthalocyanines designed for the LB technique. The identifiers are those used in the text.some representative examples, the common feature being that the Pc ring is non-uniformly substituted; one of the four benzenoid rings bears one or two substituent groups which contain a terminal hydrophilic moiety, and the other three bear simple alkyl or alkoxy substituents. All the derivatives are octa-substituted to ensure isomeric homogeneity. They fall into two main classes, hereafter referred to as the 'alkoxy amphiphiles' and the 'alkyl amphiphiles'. The compounds provide a basis for probing how the type and lengths of the hydrophilic and hydrophobic chains and the central ion pro- mote good monolayer and deposition behaviour.It transpires that the alkyl amphiphiles differ from the alkoxy amphiphiles in that they exhibit discotic mesophase behaviour, a point which is taken up later.53*54 The compounds are prepared from the appropriately substi- tuted phthal~nitriles.~~ The ether-linked phthalonitrile precur- sors are the easiest to prepare, requiring simple alkylation of dicyanohydroquinone. However, the dialkylated phthaloni- triles have a substitution pattern not readily afforded by simple substitution reactions of the benzene ring. Accordingly, these have been synthesized by ring construction using Diels-Alder reactions. Two general methods have been employed and are shown in Scheme 1. The one using furan as precursor is better suited for the incorporation of chains bearing a hydrophilic headgroup, whereas the other, using thiophene, is more con- venient for access to the simpler dialkyl phthal~nitriles.~~.'~ The amphiphilic phthalocyanines are obtained by base- catalysed condensation of a 9: 1 mixture of the appropriate pair of phthalonitrile precursors.Normally, the hydrophilic headgroups are protected during the cyclisation. The ratio of 9 :1, in favour of the phthalonitrile containing the hydrophobic chains, minimises the formation of other cross-products. Indeed, the two main products are the required non-uniformly substituted derivative and the corresponding R8 H2Pcs or (RO)8 H2Pcs. These are readily separated by column chroma- tography and can be easily converted into the corresponding M" metallated derivatives by reacting the metal-free phthalocy- anine with the appropriate metal salt.The alkoxy amphiphiles show better monolayer behaviour t 1 t NCLCNTCN TCNI 1(IV) (HO)R, MPcs Rg MPCS (HO),& MPcs. (HO'),& MPcs or (HO,C),& MPcs Scheme 1 Preparation of amphiphilic octa-alkylated phthalocyanines. (i) BuLi/RBr; (ii) BuLi/X(CH,),Br (X is protected OH or COzH group);(iii) sodium perborate; (iv) base; (v) 150"C;(vi) LiOPe/PeOH, followed by metal insertion as required. (Double arrows signify multiple steps. OTHP refers to an OH functionality protected as its tetrahydropyranyl derivative.) than the simpler (RO), MPcs.~~There is much less hysteresis in the n-A isotherm and the compressed monolayers are more stable.Fig. 6(a) and (b) compare the n-A isotherms obtained for an example of each series. The intermediate (less steep) region in the n-A isotherm for the alkoxy amphiphile, [Fig. 6(b)], may correspond to the liquid-expanded region or a phase in which the molecules are reorganising from a flat- on to a more perpendicular arrangement during compression. As the surface area is reduced further the molecules are compressed up towards the vertical, although the values for A, are sometimes larger than expected for molecules fully perpendicular to the water surface. Monolayer behaviour is marginally better for the metallated species and the isopen- tyloxy compounds give somewhat more stable monolayers than their straight-chain isomers.The length of the hydrophilic chain appears not to be a factor in controlling monolayer behaviour. However, the longer hydrophobic-chained com-pound, (H0)2(C7H150)6 H,Pc, behaved less well. The n-A isotherm is of the same general form as those of the other alkoxy amphiphiles but the surface pressure starts to rise at a higher surface area per molecule and above 25 mN m-' the film collapses. The alkyl amphiphiles having two hydrophilic headgroups show excellent monolayer behavio~r.~~,'~-'~ Those with only one hydrophilic headgro~p~~.'~ behave less well but are still much better than their simple R8 MPc analogues discussed earlier. Typically, the (HO)2R6 H2Pcs and (H@C)&, H,Pcs and their Cu" derivatives show well defined transitions from the two-dimensional gas phase to the condensed phase, the latter being characterised by a near vertical region in the isotherm, e.g.Fig. 6(c). Value? for A, in the compressed state are of the order of 120-135 A2, consistent with the molecules standing more or less perpendicular to the water surface. There is no evidence for an intervening state between the two-dimensional gas and compressed state and a further indication of the surface behaviour is provided by an X-ray reflectivity study of a monolayer of (H02C)2(C8H17)6 H,Pc.~' This revealed that the molecules are essentially perpendicular even in the uncompressed film, the monolayer film breaking up during decompression, probably to form islands and then single molecules.The contrasting behaviour of the alkyl amphiphiles and the alkoxy amphiphiles, especially the behaviour of isosteric pairs, i.e. compounds from the two series having the same number of linking atoms in the chains, illustrates the importance of the more hydrophobic alkyl chains and, arguably, the beneficial effect of the mesogenic properties conferred by these chains. The alkyl amphiphiles are examples of amphitropic materials,61 i.e. they possess two properties which lead to self-assembly; in this case, their capacity to form a mesophase and their amphi- philic character. It seems plausible that during compression, the molecules on the water surface may adopt the behaviour observed in the liquid-crystal state wherein the aromatic cores align in columns.There are also differences in the behaviour of the alkoxy amphiphiles and the alkyl amphiphiles in the LB deposition e~periment.'~However, only (HO)2(C7H&)6 H2Pc, the com- pound which showed poor monolayer behaviour, failed to deposit. Otherwise, the transfer ratios ranged from 0.7 to 1.0 for the alkoxy amphiphiles, generally better than for the (RO), MPcs, and 0.9-1.0 for the alkyl amphiphiles, a remarkable improvement over the R8 MPc derivatives which could not be deposited at all. These results clearly demonstrate the impor- tance of introducing formal amphiphilic character into the structure. The alkoxy amphiphiles tend to give wetted films which need to drain between dips. The straight-chain pentyloxy derivatives, (HO)2(C5H,,O)6 MPcs, undergo Y-type deposition during the first dipping cycle followed by Z-type deposition on subsequent cycles.Chain branching improves the deposition such that (HO)~(~SO-CSH,,O)~ MPcs and (H0')2(i~~-C5H110)6 J. Muter. Chem., 1996, 6(5),677-689 681 30 2s a0 15 LO S 0 0 I so \ lo0 I-1SO 200 1 2so -1 (b) h so 1m 2so0 area per moIecuIe/A* Fig. 6 n-A Isotherms showing the variation of the surface pressure as the area occupied by the surface molecules is varied The area is first reduced and then expanded (a) isotherm for (C,H,,O), H2Pc, (b)isotherm for (H0)2(~~~-C5H110)6HzPc [less hysteresis than (a)], (c) isotherm for (H0)2(C10H21)6H2Pc which shows minimal hysteresis and an absence of an intermediate 'two-dimensional liquid phase' Adapted by permission from ref 54 MPcs consistently undergo Y-type deposition to form even green filmss4 The evenness of the transfer process is evident from the linear increase of the visible region absorbance with the number of dips62 Members of all four series of alkyl amphiphiles behave especially well and, indeed, much better than the alkoxy amphiphiles All exhibit Y-type deposition to give very even films with little apparent wetting after emersion Low-angle X-ray diffraction studies of films of alkoxy amphi- philes give no Bragg peaks, indicating little or no layer ordering However, in some cases Kiessig fringes are observed which indicate evenness of the film and analysis of the data provides a measure of the film thickness Dividing this by the number of Y-type dips provides a measure of the thickness of film deposited per dip, ip the case of the alkoxy amphiphiles this is typically 20-23 A 54 Films of alkyl amphiphiles give different results The films show two or three Bragg peaks corresponding to spacings for the Y-deposited bilayers of 25 A for (HO)2(C6H13)6 H,Pc and then ranging from ca 40A to 43 5 A for the longer-chain analogues The estimated distance, w, from the hydrophilic groups to the end of fully extended alkyl chain! on the opposite side of the molecules is between 23 and 25 A depending upon the number of carbon atoms in the alkyl chains Clearly, the measured value for the bilayer spacing is less than 2w, indicating that the molecules are to some extent tilted and/or there is interdigitation of the chains of molecules in adjacent layers The markedly smaller bilayer spacing in the film of (H0)2(C6H13)6 H2Pc cannot be explained simply in terms of the length of the substituent chains It points to a different packing type Whether or not the rings are tilted can be assessed by IR spectroscopic techniques, proven tools for probing orientations of molecules within thin film assemblies supported on appro- priate substrates Various experiments are possible and several are complementary As an illustration, in a normal incidence transmission spectrum of a film deposited on an IR-transparent substrate such as silicon, the electric field vector interacts with transition moments which are parallel to the substrate surface On the other hand, when reflection-absorption IR spec-troscopy (RAIRS) is used to probe a film supported on a metal surface such as gold, only those vibrational modes having a component normal to the substrate surface will absorb radiation Phthalocyanine thin films are ideally suited for IR analysis, not least because the rigidity of the planar Pc nucleus ensures that the directions of out-of-plane and in- plane transition dipoles associated with the nucleus are all well defined This facilitates analysis of the orientation of the molecules with respect to the interrogating beam Debe's 64 and others6' have explored the application of RAIRS for studies of sublimed films of unsubstituted derivatives, probing both the mean orientation of the rings relative to the substrate and the degree of order, and there have been several studies of phthalocyanine LB films 66 IR techniques demon- strate conclusively the contrasting molecular packings in LB films of the alkoxy and alkyl amphiphiles 69 The transmission and RAIR spectra for films of (H0')2(i~~-CsH110)6 CuPc are very similar, which suggests that either there is little anisotropy in the orientation of the molecules relative to the substrate, or the molecules are tilted at 45" The absence of layer spacing referred to earlier suggests that the first interpretation is more likely IR experiments with the alkyl amphiphiles give rather different results Fig 7 compares the KBr disc spectrum for (H02C)2(C10H21)6H2Pc, the normal incidence transmission spectrum of the LB film on silicon and the RAIR spectrum of the LB film on gold The band at ca 760 cm-I is assigned to an out-of-plane vibration (arising from either an aromatic C-H or the macrocyclic ring deformation) and therefore its dynamic dipole moment is polarised perpendicular to the plane of the macrocycle The band is strong in the transmission spectrum and virtually absent in the RAIR spectrum This is consistent with the molecules being oriented with the plane of 682 J Mater Chem ? 1996, 6(5), 677-689 I1830 1700 1570 l't't0 1310 1180 lOS0 920 $90 660 v/ cm-' Fig.7 (a) IR absorbance spectrum of a pressed pellet of (H0,C)z(CloHzl)6H,Pc in KBr.(b)RAIR spectrum of an LB film of (Ho,C),(c1,&~1)6 H,Pc on a gold surface. (c) Normal incidence transmission spectrum of an LB film of (Ho~C)~(c&~1)6H,Pc supported on silicon. Reproduced (with modification) by permission from a diagram in ref. 69. the ring perpendicular to the substrate surface. Similar IR studies have been performed on the films of the (HO),R, MPcs and have yielded the same conclusions. Further experiments have given information about aniso-tropic packing of molecules within a molecular layer.69Fig. 8 shows the normal incidence transmission spectra of the LB film of (Ho&),(cloH,1)6 H,Pc on silicon with the electric field vector polarised parallel and perpendicular to the dipping direction. The 760 cm-l band is very intense in the former but is much diminished in the latter.This shows that the mean orientation of the molecules is one where the angle p between the normal to the plane of the ring and the dipping direction, d, is significantly less than 45". The dynamic dipole moment for an out-of-plane vibration at an angle p to d will have components perpendicular and parallel to d. The ratio of the absorption intensities Z,,and ZI, about 5, is given by cos2 P/sin2 P, whence /3 is ca. 25". The films of the alkoxy amphiphiles and alkyl amphiphiles __c Directton of the dynamic dipole 01 the ca 760cm ' bandq.-Molecular planed1 d is the dippng direction n Ii 1 if90 1660 I530 lkOO 1270 Ilk0 ldl0 880 750 620 v km-' Fig.8 The anisotropic alignment of the (H02C)2(C10H21)6H,Pc mol-ecules in the molecular monolayers can be detected by polarised IR beam experiments. The plots show the transmission IR spectrum of an LB film of (H02C)z(CloHzl)6H,Pc supported on silicon with the electric field vector of the beam polarised parallel (top spectrum) and perpendicular (bottom spectrum) to the dipping direction. The inset diagram shows a representation of the mean orientation, ct, of the rings to the dipping direction. The ratios of the relative intensities of the band at ca. 760 cm-' indicate that p, the mean angle of the normal to the ring to the dipping direction, is ca. 25". Reproduced by permission from ref. 69. give rise to three distinct types of visible region absorption band envelope.54Examples are shown in Fig.9 and each differs from the spectral band shape depicted in Fig. 3, demonstrating that the in-layer molecular packing is quite different from that for the tri-and tetra-substituted compounds discussed earlier. The band shape shown in Fig. 9(a) is typical of the spectra exhibited by LB films of the alkoxy amphiphiles. The more 10 500 0 450 I 0 400 4 A:350 i 0 300 -0 250 -O *0° 1 0 000l050I-dd-4 550.00 600 00 650.00 700 00 750.00 000 00 500 00 050 00 1 000 j t 0 900 - (b 1 A 0.800 - 0.700 - P) 0.600 C g 0 500 fna m 0.400 0.300 0.200 0 100 0.000 550 00 600 00 650 00 700.00 750.00 800 00 500 00 850 00 1 1 I 10 500 t 1 0 60 -(c) 0 400 -0 350 -0 300 -0 250 -0 200 -0 10001501 o.ow1 nJ\ I0 000 550 00 600 00 650 00 700 00 750 00 800 00 500 00 850.00 A/nm Fig.9 Visible region spectra of LB films on glass slides. (a)(HO),(iso-C5Hllo)6 cupc; (b) (H0)2(C6H13)6 H2Pc; (c) (H0)2(C9H19)6 cupc.Spectra are recorded with the electric field vector polarised (A) perpendicular to the dipping direction, E, and (B) parallel to the dipping direction, El,.The third line (C) in each plot corresponds to the solution phase spectrum which is shown for comparison. Adapted by permission from ref. 54. J. Mater. Chem., 1996, 6(5),677-689 683 intense component appears at ca 755 nm for metal-free denva- tives and at ca 740nm for copper derivatives These are broader and red shifted relative to the band positions in the spectra of the compounds in solution A red shift is to be expected for an assembly of phthalocyanine molecules in which the adjacent rings within a columnar structure are offset, ze the molecules are not aligned fully cofacially Some spectra, notably those of films where the alkoxy group is isopentyloxy, show dichroism suggesting that there is some degree of aniso- tropic alignment with the molecules showing a preference for alignment with their planes perpendicular to the dipping direction The two types of spectral band envelope exhibited by films of the alkyl amphiphiles are illustrated in Fig 9(b) and (c) The former is observed for LB films of (HO),(C,H,,), H,PcS4 and (HO),(iso-C,H,,), H,Pc 58 The main feature of the spectrum is the relatively narrow red-shifted absorption which again is consistent with non fully cofacially aligned stacking of mol- ecules within a columnar assembly There is dichroism, with a higher dichroic ratio than that observed for the films of any of the alkoxy amphiphiles Fig 9(c) shows the type of band structure exhibited by longer-chained homologues of the (HO),R, H,Pc and (HO,C),R, H,Pc series and their Cu" derivatives This is very different from that in Fig 9(b) and confirms that the type of packing is sensitive to the length of the alkyl chains There are two main absorption bands centred at ca 635 and 768 nm, and two lower intensity transitions, one to the red and one to the blue of the 635 nm band Spectra of the films of these types of compound all show dichroism such that R is > 1 for the 635 nm band and < 1for the 768 nm band, the magnitude of R at the two wavelengths varying slightly for films of different compounds The evident splitting of the visible region transition into red-shifted and blue-shifted components and the opposite dichroism for the two bands is indicative of Davydov splitting (exciton splitting) arising from translationally non-equivalent molecules within the 'unit cell' An example of such packing is the 'herring-bone' structure referred to earlier Interestingly, this type of Davydov split absorption is also observed for the horizontally lifted LB films of the peripherally substituted octaalkyl phthalocyanines 49 Other longer-chained alkyl amphiphiles with Ni as the central atom show a similar band structure and dichroism but the exciton splitting of the band into the red- and blue-shifted components is lower, indicating some differences in packing or spacing within the columnar assembly Spin-coated Films The technique of spin-coating or spin-casting involves the evaporation of a drop of a solution of a compound in an organic solvent on a substrate rotating at speeds of ca 2000rpm As the solution is spread by centrifugal force, the solvent evaporates leaving the solute as a 'spin-coated' film Films of some tetra-substituted neopentyloxy derivatives obtained in this way have been shown to have a lower percentage area coverage of crystallites than a simple evapor- ated film7' Spin-coated films of AmPc1 (see Fig 2 for the structure) have been compared with the LB film of the same material (see Langmuir-Blodgett Films, earlier) The spin- coated film shows a blue-shifted band at 603 nm, attributed to a columnar stacking of 18 7 molecules, cf 14 4 for the LB film4546 However, the electrical properties of the two films suggest that overall the spin-coated film may be less well ordered, the LB film shows a conductivity of an order of magnitude higher 71 The solubility of the R8 MPcs in solvents such as THF and especially toluene renders these compounds also suitable for spin-coating They form particularly even films and there is no evidence of crystallites on viewing the film under a microscope There is, moreover, good evidence for molecular self-assembly 684 J Muter Chern , 1996, 6(5), 677-689 into an ordered film structure insofar as X-ray reflectivity studies reveal diffractions attributable to layering of molecules within the films The spacings are of the order of 17-18 A, depending upon the compound deposited The values are lower than the effective diameters of theSompounds in their discotic columnar mesophases (ca 22-23 A) which may reflect a more compressed structure in which the side chains are either less fully extended or more interdigitated with those of adjacent molecules Alternatively, it may indicate some tilting of the planes of the molecules from the perpendicular to the substrate 72 Remarkably, the visible region spectra reveal very similar band envelopes to those of LB films of the corresponding alkyl amphiphiles having the same length of alkyl chains Thus the spectra of the spin-coated films of (C6H13)8 H,Pc and (CgH1-)8 H,Pc (the latter shown in Fig 10) show the same band shapes as the LB film spectra of (H0),(C,Hl3), H,Pc and (HO),(C8Hl7), H,Pc, respectively A spin-coated film of a 1 1 mixture of (C6H13)8 H,Pc and (C8H17)8 H,Pc gives a film having the same spectrum as the former 73 These experiments point to the fact that the length of the alkyl chains is quite crucial in controlling film structure in both spin-coated and LB films Subsequent studies showed that this applies quite generally to the solid-state formulation of these materials When crystals of the different R8 MPcs are pressed onto a glass slide to give a thin smeared film, they give rise to spectra very similar to those of the corresponding spin-coated film Furthermore, when the crystals are smeared in one direction only, the spectrum shows dichroism 74 Yet another indication that spin-coating generates molecular packing which approxi- mates to that in the crystal state, at least over short range, is forthcoming from the observation that cooling a thin liquid layer of (C8H17)8 H,Pc on a glass slide produces a crystallised film having the same spectral characteristics as the spin-coated film 75 At the present time, the precise type of packing in the films and, indeed, the crystal state remain to be determined, to date only one crystal-structure determination has been achieved, that of (C6H13)8 H,Pc This reveals that the molecules 1 coo , .1 0 0 0 0 -0 500 400 1 ' c 1 1 000 J -f--1[a):;. , 0 200 0 000 50 100 150 170 TI% Fig. 10 A, Spectra of the spin-coated film of (C8H17)6H,Pc at tempera- tures which correspond to different states (a) 50°C the crystal state, (b) 90 "C the columnar mesophase of rectangular symmetry, (c) 145 "C, the columnar mesophase of hexagonal symmetry, and (d) 160°C the isotropic liquid phase B, Plot of the change of absorbance at 714 nm plotted as the temperature of the film is raised, (a)-@) as in A The fall in absorbance on heating the materlal in the liquid state is due to material flowing down the slide are aligned in columnar stacks in which the planes are tilted with respect to the column axis, i.e.they are not fully cofacially stacked. The tilts in the column are in the same sense in adjacent columns as in a J-sta~k.~, Compounds with longer chains, i.e. those which give spectra for the solid state showing the red- and blue-shifted bands, have been obtained only as fibrous needles, unsuited for single-crystal X-ray studies. Examples of the alkyl amphiphiles also give very even spin- coated film^.^^,^, Low angle X-ray reflectivity measurements of a film of (H0'),(C8H17), H,Pc show six sharp Bragg peaks which index as the 001, 002 and 004 reflections fr:m two different repeat units.77 The spacings are 37 and 44A.Thus there are two different types of packings co-existing and the magnitudes of the d spacings somewhat surprisingly indicate that these are both 'bilayers', implicating hydrogen-bonding participation during the self-assembly process. The correspond- ing LB film of the compougd contains a bilayer structure with a repeat spacing of 43.5 A. Despite these differences in the packing of the two films, they give the same spectral band shape in the visible region, showing that the feature of the packing which gives rise to the exciton splitting is retained. From this it may be inferred that the exciton splitting arises through interaction between molecules within the same mol- ecular layer rather than in adjacent layers.Thermally Induced Molecular Reorganisations in Films As both the R, MPcs, R, H,Pcs and the alkyl amphiphiles exhibit thermotropic liquid-crystal behaviour as crystalline materials, it is to be expected that the molecular assemblies within the films might undergo molecular reorganisations on heating. This is indeed the case.78 The visible region spectra of the spin-coated films of examples of the R, MPcs, R, H,Pcs and the (HO),R, H,Pc series undergo sharp changes at or close to the mesophase transition temperatures of the bulk material. These are fully reversible provided the films are not heated into the liquid phase where the evenness is lost. Spectra of a spin-coated film of (C8H17), H,Pc, at temperatures corre- sponding to different phases, are shown in Fig.10A. Fig. 10B shows the change in absorbance at 714nm with temperature, the marked changes corresponding to the transition from the crystal state, through two mesophases, to the liquid phase. Heating LB films of the alkyl amphiphiles produces more complex behaviour. An analysis of the behaviour of the LB films of a series of (HO),R6 H,Pcs indicates that the films of the monotropic liquid crystals, i.e. materials which develop a discotic mesophase only during cooling, differ from those of the enantiotropic liquid crystals, which exhibit a mesophase during both heating and cooling. Films of the former series tend to melt at temperatures very close to those of the bulk material; those of the latter show gradual molecular reorganis- ations at temperatures in the ranges corresponding to the mesophase of the bulk materials and melt below the tempera- ture required to melt the bulk material into the liquid phase.Fig. 11 shows the variation of the absorbance at a set wave- length with change of temperature for the two types of film of (HO)2(CgH1,), H,Pc. The transitions evident for the spin- coated film correspond to the phase transitions of the bulk material; for the LB film there is a change in the spectrum but this occurs more gradually over a much broader temperature. The LB film also has a lower melting point into the liquid phase. When the LB films of the (HO),R, H,Pc materials are cooled from a temperature below their melting temperatures they show broadly reversible behaviour, giving room tempera- ture spectra similar to the spectra of the freshly deposited film.Sometimes there are small shifts of the two principal bands and enhanced di~hroism.~~,~~ Similar behaviour is also exhibited by the LB film of I. 100 1.000 8 0.900 C f!0.800 $13 a 0.700 0.600 0.500 0.400 -j 80 100 120 TIT Fig. 11 Plots showing the change of absorbance at 707 nm on heat- ing: -, a spin-coated film; ----, a LB film of (H0)2(C9H19)6H2Pc. The drop in absorbance on heating the latter at high temperature corresponds to the melting of the film. (H02C)2(CloH21)6H,Pc. However, films of two of the shorter- chain materials of this series behave differently insofar as heating generates a new molecular assembly which is retained The LB film of (H02C)2(C8H17)6 on ~ooling.'~,~~ H,Pc, for example, gives rise to a spectrum very similar to that for the spin coated film of (C&t17)8 H,Pc [Fig.lO(u)]. The LB film assembly undergoes a molecular reorganisation at 127.5 "C which results in a change to one very similar to that for the columnar hexagonal mesophase of (C,H17)6 H,Pc [Fig. 1o(c)]. The new band shape is retained on cooling though there is a small (5 nm) blue shift of the individual transjtions. There is also a reducFion in the bilayer spacing from 41 A in the original film to 36 A in the heat-treated film.56 The changes in the spectrum imply that the molecules in the film have adopted a similar packing to that in the columnar hexagonal mesophase; that this is retained on cooling is perhaps attributable to stabilisation of this packing through hydrogen bonding involv- ing the carboxylic acid groups.Spin-coated Films of More Complex Mesogenic Pht halocyanines The alkyl amphiphiles are ideally functionalised to form more complex structures, the hydroxy function, for example, of the (HO)R7 MPcs and (HO),R6 MPcs providing a means of linking the phthalocyanine moiety to other units, not least to further phthalocyanine rings. Organic-solvent-soluble deriva- tives retaining mesophase-forming behaviour have indeed been prepared and include liquid-crystalline ferrocenyl-phthalocyan- ines,,' and ester-linked liquid-crystalline dimers, trimers" and main-chain polymers,82 e.g. Fig.12. The spin-coated film of the ferrocenyl-phthalocyanine is smooth and even and has a Q-band absorption very similar to that of the spin-coated film of the (HO)R7 MPc precursor, suggesting that the ferrocenyl unit has not disrupted the packing significantly. The film undergoes reversible changes on heating and cooling" and the behaviour of the ferrocenyl group in these different environ- ments is under examination. The dimers and trimers as bulk materials generate a meso- phase on heating which is retained on cooling to room temperature when the compounds become highly viscous.81 Both series are poor materials for LB deposition but give very good spin-coated film^.^^,'^ X-Ray reflectivity profiles from films of examples of a dimer and a trimer show well defined Kiessig fringes implying uniform thickness.They also show a feature in the profile consistent with either a rectangular or hexagonalo columnar 'lattice' with an intercolumnar distance of ca. 23 A. The band structures in the visible region spectra J. Muter. Chem., 1996, 6(5), 677-689 685 Fig. 12 Structures of examples of liquid-crystalline ferrocenyl-phthalocyanines and phthalocyanine dimers and tnmers which deposit well as spin- coated films of the films for the dimer and trimer are broadly similar to that exhibited by the alkyl amphiphiles in their mesophase range Thus, as the solvent evaporates during the spinning process, the molecules appear to assemble to give a room-temperature packing which is quite different from the room- temperature packing of the simpler materials Self-assembled Monolayer Films A fast developing area of thin film research is the formation of a self-assembled monolayer (SAM) at the surface of an appropriate substrate 29 These ultrathin films, one molecule thick, are chemically bonded to the surface and are thus potentially more robust than LB or spin-coated films Typical methodologies include the reactions of thiols and disulfides at gold or silver surfaces and of trichlorosilylalkyl derivatives on glass or silicon Much of the fundamental work has been performed on simple functionalised alkanes2' but now there is increasing attention given to depositing SAMs of compounds with properties which are potentially more interesting with regard to applications The alkyl amphiphiles can be used as precursors to derivatives appropriate for SAM deposition through conversion of the hydroxy function into the corre- sponding thiol or disulfide This is achieved by routine chemis- try and these derivative^^^ form good SAM films on gold surfaces The films are best characterised by FTIR techniques Fig 13 shows the C-H stretching region of the RAIR spec- trum obtained for the SAM film obtained using a disulfide derivative 85 Attachment of a phthalocyanine SAM film to the surface of a silicon wafer and a glass slide has been achieved using non-uniformly substituted phthalocyanines bearing one or two trichlorosilylalkyl groups 86 The compounds, in solu- tion, react with the surfaces of substrates rendered hydrophilic pnor to deposition Deposition onto glass enables the films to be monitored by visible region spectroscopy which shows an absorption band with an absorbance of ca 0004 for the monolayer Applications in Gas Sensing Devices Gas sensing continues to be a particularly promising area for exploiting phthalocyanine thin films in practical devices The first demonstration by Roberts' group of the effectiveness of an LB film of Pam-CuPc as a conductiometnc NO, gas sensor has been followed by a number of other studies33 Typically, the film is deposited onto a substrate bearing interdigitated electrodes and exposed to pulses of low concentrations of gases mixed with air Among the many interesting results obtained, it has become apparent that there are significant differences in behaviour between LB films of substituted phthalocyanines and sublimed films of unsubstituted phthalocyanines For example, relative to the latter, LB films of tetraaryloxy deriva- tives show a lower response to electron-acceptor gases but a higher response to electron-donor gases In one instance, the conductivity of an LB film of copper tetra-4-( 2,4-di-tert-amyl- phenoxy)phthalocyanine has been shown to be insensitive to 200ppm of NO, and SO, whereas there is a significant response upon exposure to ammonia87 Films of the alkyl amphiphiles, on the other hand, show a good response to NO, in the range 1-5 ppm and limited response to ammonia up to concentrations of 25 ppm 88 89 These concentrations are within the occupational hygiene ranges prescribed by the UK's Health & Safety Executive (HSE) Typical output from experiments performed at the HSE laboratories on devices constructed from LB films of the alkyl amphiphiles is shown as Fig 14 Changes in current flow are monitored over time The baseline current is established by measuring the film current in clean air over two minutes The film is then exposed to the analyte gas, in air as carrier, for two minutes and this is followed by a two minute recovery time in clean air The latter cycle is then repeated four times using either the same or different concentrations of gas The first two plots of Fig 14 show the results of five exposures of a film of (HO),(C,H,,), H2Pc to 3 ppm NO, followed by five exposures to another gas The remaining plots show part of a series of repetitions of this ten-exposure cycle There is encour- aging selectivity with no response to chlorine or CO, and limited responses to ammonia, H2S and SO, in the occu-pational hygiene ranges Importantly, the devices continue to respond to NO, after exposure to the other gases and their operation is not diminished by exposure to air with 40% relative humidity, a problem sometimes encountered with films of unsubstituted phthalocyanines It seems plausible that the hydrophobic alkyl chains serve to protect the film from moisture The anisotropic deposition of the molecules in the LB experiment which gave rise to the dichroism in the visible regon and FTIR spectra discussed earlier is also manifested in the conductivity measurements Thus there is a different level of response to NO, gas when LB films of (H0)2(C,H,3)6 H,Pc are deposited with the dipping direction perpendicular and parallel to the long arms of the electrodes [Fig 15(a)] The larger response, by a factor of ca 7 [Fig 15(b)] arises in the former case where it is supposed that the axes of columns within the molecular layers are predominantly perpendicular to the long arms of the electrodes The results are thus consistent with conduction occurring along the columns 89 There is clearly scope for further work in this area which may turn up surprising effects indeed, preliminary results have shown that films of an alkoxy amphiphile show an unexpected conductiometric response to toluene Future Prospects and Developments Much has been achieved in developing thin films of substituted phthalocyanines in the dozen or so years following the Durham 686 J Mater Chem , 1996, 6(5),677-689 -.0074 I 3800 3600 3400 3200 3000 2800 2600 2400 2200 v/cm-' Fig.13 Part of the RAIR spectrum of a phthalocyanine SAM film on a gold surface. The film was obtained by immersing the gold-coated glass slide into a solution of the disulfide derivative shown. The three C-H bands are assigned as follows: 2856cm-', CH, symmetric stretch; 2927 cm-', CH, asymmetric stretch; 2968 cm-', CH, in-plane asymmetric stretch.Adapted by permission from ref. 85. Air Gas Air Gas Air Gas Air Gas Air Gas Air +#+it+t++G+ 8 10-82 ?!= 3 0 t0 li~/secS (a) five sequenhal pulses of 3ppm NO2 A c ?! -3 0 0 0 t Timdsecs (b) five sequential pulses of 0.625ppm Cl2 8.104 sz= 30 0 0 t Timdsecs (c)five sequential pulses of 3ppm NO2 8.,lo-*2 -?! -50 0 0 t TirneJ/seCs (d) fwe sequential pulses of 5Oppm CO O 0 t 0 Timelsecs (e) five sequential pulses of Bppm NO2 1320 1320 1320 1320 a1320 Fig. 14 Sequential exposure of an LB film of (H0),(CSH13), H,Pc deposited onto interdigitated electrodes (Fig. 15) on a glass substrate. The plots show the changes in current flow during exposure.The curved line in the second plot arises from the continued 'recovery' of the film from the final exposure to NO, in the first plot. Reproduced with permission from ref. 89. group's first publications on phthalocyanine LB deposition. The present article has reviewed some, but by no means all, of the contributions. What is clear is that the field has attracted scientists from a number of disciplines with progress in syn- thetic chemistry leading to a range of novel compounds which can be deposited to produce LB films with a satisfactory degree of molecular order. Furthermore, films can now be constructed with different molecular packings and there is increased knowl- edge of how substituents can be used to control the packing.Undoubtedly, there is scope for examining the extent to which the central metal or metalloid atom can influence packing, as it surely must. Reports of spin-coating of phthalocyanine films in the open literature are relatively few, but the convenience of the technique has attracted the attention of industrial and applied groups. Furthermore, the reports that are available suggest that appropriate compounds can give rather well lppm NO2 Pppm NO2 Bppm NO2 4ppm NO2 5ppm NO2A&$irp%r~;~;\; 0 t 1320 Time/secs Fig. 15 Schematic representation of an array of interdigitated elec- trodes patterned onto the glass substrate for use in the LB experiment. Lower plot: results for 30 layer films of (HO),(C,H,,), H,Pc exposed to 1, 2, 3, 4 and 5 ppm NO, for films dipped (a) perpendicular, and (b) parallel to the arms of the electrodes.Reproduced with permission from ref. 89. J. Muter. Chem., 1996,6(5), 677-689 687 ordered films, albeit of a lesser calibre than LB films However, it is the third type of film discussed in this article, the self- assembled monolayer, which seems likely to attract more immediate attention inasmuch as SAM research in general is receiving a high profile at this time In the three areas of film research discussed here, there is a particular need for further 20 21 22 23 24 C J Brown, J Chem SOC A, 1968,2494 M Ashida, N Uyeda and E Suito, Bull Chem SOC Jpn, 1966, 39,2616 T Kobayashi and S Isoda, J Muter Chem , 1993,3,1 J H Beynon and A R Humphnes, Trans Faraday SOC, 1955, 51,1065 P T Cardew and R J Davey, Proc R SOC London Ser A, 1985, studies to identify unambiguously the finer details of the packings obtained to date, as yet there have been rather few applications of advanced microscopies to the problem A survey of the potential applications of the three types of film was beyond the scope of the present article but a few 25 26 27 28 398,415 F Iwatsu, J Phys Chem, 1988,92, 1678 J H Sharp and M Lardon, J Phys Chem, 1968,72,3230 R 0 Loutfy, Can J Chem, 1981,59,549 S Dogo, J-P Germain, C Maleysson and A Pauly, Thin Solid Films, 1992,219,244,251 observations are offered nevertheless The exploitation of 29 R H Tredgold, J Muter Chem, 1995,5,1095 See also A Ulman, phthalocyanine films in gas sensors is likely to remain a key area of research Emphasis may well change from con-ductiometnc to optical sensors and, indeed, there are a number of laboratories already devoting effort towards devising sensing devices exploiting various optical effects, e g the surface plas- 30 31 32 An Introduction to Ultrathin Organic Films from Langmuir- Blodgett to Self-assembly, Academic Press, San Diego, 1991 A Hughes, Proc R SOC London Ser A, 1936,155,710 A E Alexander, J Chem SOC ,1937,1813 S Baker, M C Petty, G G Roberts and M V Twigg, Thin Solid Films, 1983,99, 53 mon resonance phenomenon In principle, optical sensors have 33 S Baker, G G Roberts and M C Petty, IEE Proc Part I Solid- various advantages over conductiometric sensors, especially where there are fire hazards in the environment where the sensor is to be used There is a need, however, in both the conductiometric and the optical sensing areas for more empha- sis to be given to their marketability, perhaps by focusing on their incorporation into sensing units already available Redox behaviour in thin films of phthalocyanines deposited onto electrodes is an ongoing area of research which will continue to attract attention Electrochromism has already been men- tioned in passing in the text and the extensive progress which has been made to date, especially on the rare-earth-metal 34 35 36 37 38 39 40 State Electron Devices, 1983, 130,260 J Batey, M C Petty, G G Roberts and D R Wight, Electron Lett, 1984,20,489 G G Roberts, M C Petty, S Baker, M T Fowler and N J Thomas, Thin Solid Films, 1985, 132, 113 H Yamamoto, T Sugyama and M Tanaka, Jpn J Appl Phys, 1985,24, L305 R D George, P F McMillan, V A Burrows and R Hervig, Thin Solid Films, 1991,203, 303 E Kanezaki, Mol Cryst Liq Cryst Lett, 1988,5,101 E Kanezaki, J Coord Chem ,1988,18,113 W Yan, Y Zhou, X Wang, W Chen and S Xi, J Chem SOC Chem Commun , 1992,873 phthalocyanines, awaits transfer to working devices Further work is also required to improve the performance of phthalocy- anine films in non-silicon based photovoltaic cells and in photochemical cells In such devices the macrocycle is used for both photon capture and to conduct or transfer charge to a second species, compounds have already been shown to be 41 42 43 44 K Nichog, K Waragai, A Taomoto, Y Saito and S Asakawa, Thin Solid Films, 1989,179,297 K Ogawa, H Yonehara, T Shoji, S-I Kinashita, E Maekawa, H Nakahara and K Fukuda, Thin Solid Films, 1989,178,439 K Ogawa, S-I Kinoshita, H Yonehara, H Nakahara and K Fukuda, J Chem SOC Chem Commun, 1989,477 H Itoh, T Koyama, K Hanabusa, E Masuda, H Shirai and useful catalysts for the photochemical decomposition of water Future developments may well benefit from matenals purpose- designed to give broad-band absorption in the visible region to optimise photon capture 45 46 47 T Hayakawa, J Chem SOC Dalton Trans, 1989,1543 M Fujiki, H Tabei and S Imamura, J Phys Chem ,1988,92,1281 M Fujiki, H Tabei and T Kunhara, Langmua, 1988,4, 1123 M Yoneyama, M Sugi, M Saito, K Ikegami, S-I Kuroda and S Iizima, Jpn J Appl Phys, 1986,25,961 48 D W Kalina and S W Crane, Thin Solid Films, 1985,134, 109 49 H Nakahara, K Fukuda, K Kitahara and H Nishi, Thin Solid References Films, 1989,178,36 1 2 F H Moser and A L Thomas, The Phthalocyanines vol 2 Manufacture and Applications, CRC Press, Boca Raton, FL, 1983 Phthalocyanines-Properties and Applications, ed C C Leznoff and A B P Lever, VCH Publishers, New York, 1989 50 51 N B McKeown, M J Cook, A J Thomson, K J Harmon, M F Daniel, R M Richardson and S J Roser, Thin Solid Films, 1988,159,469 M J Cook, A J Dunn, M F Daniel, R C 0 Hart, R M Richardson and S J Roser, Thin Solid Films, 1988,159,395 3 4 P Gregory, High-Technology Applications of Organic Colorants, Plenum Press, New York, 1991, ch 7, p 59 J E Kuder, J Imaging Sci ,1988,32,51 52 53 eg T Sauer, T Arndt, D N Batchelder, A A Kalachev and G Wegner, Thin Solid Films, 1990, 187, 357 I Chambrier, M J Cook, S J Cracknell and J McMurdo, 5 R Ao, L Kummert and D Haarer, Adv Muter, 1995,5,495 J Muter Chem, 1993,3,841 6 7 J D Wnght, Prog Surf Sci ,1989,31,1 A W Snow and W R Barger, in ref 2, p 341 54 M J Cook, J McMurdo, D A Miles, R H Poynter, J M Simmons, S D Haslam, R M Richardson and K Welford, 8 9 D Wohrle and D Meissner, Adv Muter, 1991,3,129 A B P Lever, M R Hempstead, C C Leznoff, W Lui, 55 J Muter Chem ,1994,4, 1205 N B McKeown, M J Cook and I Chambrier, J Chem Soc M Melnik, W A Nevin and P Seymour, Pure Appl Chem ,1986, Perkin Trans I, 1990,1169 58,1467 56 N B McKeown, M J Cook, A J Thomson, K J Harrison, 10 C S Frampton, J M O’Connor, J Peterson and J Silver, M F Daniel, R M Richardson and S J Roser, Thin Solid Films, Displays, 1988, 174 1988,159,469 11 I Rosenthal and E Ben-Hur, in ref 2, p 393 57 M J Cook, N B McKeown, J M Simmons, A J Thomson, 12 R Bonnett, Chem SOC Rev, 1995,19 M F Daniel, K J Harmon, R M Richardson and S J Roser, 13 C C Leznoff, in ref 2, p 1 J Muter Chem, 1991,1,121 14 J Simon and P Bassoul, in Phthalocyanines-Properties and Apphcatzons, ed C C Leznoff and A B P Lever, VCH Publishers, 58 59 I Chambner, unpublished results M J Cook, J Muter Sci Muter Electron, 1994,5, 117 15 New York, 1993, vol 2, p 223 F H Moser and A L Thomas, The Phthalocyanines Vol 1 60 N Dent, M J Grundy, R M Richardson, S J Roser, N B McKeown and M J Cook, J Chim Phys, 1988,85,1003 Properties, CRC Press, Boca Raton, FL, 1983, ch 1, p 1 61 H Ringsdorf, B Schlarb and J Venzmer, Angew Chem Int Ed 16 M J Cook, in Spectroscopy of New Materials, eds R J H Clark Engl, 1988,113,27, A Laschewsky, Angew Chem Int Ed Engl, and R E Hester, Wiley, Chichester, 1993, p 87 1989,28,1574 17 18 T Kobayashi, Y Fujiyoshi, F Iwatsu and N Uyeda, Acta Crystallogr Sect A, 1981,37,692 H Saijo, T Kobayashi and N Uyeda, J Crystal Growth, 1977, 40,118 62 63 S Mukhopadhyay, A K Ray, M J Cook, J M Simmons and C A Hogarth, J Muter Sci Muter Electron, 1992,3, 139 M K Debe, J Appl Phys, 1984, 55, 3354, erratum M K Debe and T N Tommett, J Appl Phys ,1987,62,1546 19 R Mason, G A Williams and P E Fielding, J Chem SOC Dalton 64 M K Debe, R J Poiner and K K Kam, Thin Solid Films, 1991, Trans, 1979,676 197,355 688 J Muter Chem , 1996, 6(5),677-689 65 J.Dowdy, J. 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ISSN:0959-9428    

DOI:10.1039/JM9960600677

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Preparation of ultrafine particle multilayers using the Langmuir-Blodgett technique Tadao Nakaya," Yu-Jun Li and Kazunori Shibata Department of Bio-applied Chemistry, Faculty of Engineering, Osaka City University, 3-3-1 38, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan X-Type Langmuir-Blodgett multilayers of magnetic ultrafine particles such as 100 A magnetite (Fe,O,), 1000 A y-diiron trioxide (y-Fe203), 70 A titanium dioxide (Ti02), 500 A barium ferrite (BaFe1201g), and ultraconducting fine-particle Y-Ba-Cu have been prepared. They were dispersed in oleic acid or stearic acid in a ballmill. The dispersed products were assembled into LB multilayers deposited onto a fresh poly(ethy1ene terephthalate) or MgO film plate. The morphology of the LB multilayers of the ultrafine particles was investigated by high-resolution transmission electron microscopy and scanning electron microscopy and it was found that they have fine lamellar structures.In addition, the obtained multilayers have magnetic anisotropy behaviour observed by magnetic property measurements. Magnetic ultrafine particles have been widely applied in mag- netic recording films, e.g. audio, video, cassette tape and floppy disks, based on ultrafine particle thin films. Moreover, ultracon- ducting fine particles have already attracted much attention, and natural magnetotactic bacteria have also been found within intracytoplasmic membrane vesicles.' Therefore, the preparation of ultrafine particle thin films is of great interest. Among the many methods for preparing ultrafine particles, e.g.in gla~ses,~.~ polymer^,^ Langmuir-Blodgett (LB) films,5 zeolites and and mesoporous silicate^,^ the LB tech- nique is a convenient method and there is much current interest in LB multilayers of ultrafine particles. The usual ultrafine particles cannot be fixed since it is difficult to combine their hydrophilic surfaces. In addition, they are also unstable since the suspended states of various ultrafine particles are different on the surface of water. Accordingly, it is necessary to modify the magnetic ultrafine particles, e.g. by using surfac- tants, before they are used to prepare the LB multilayers. The groundwork for LB multilayers of magnetic particles has been established by Fendler and co-workerslO,ll and Yang et ~1.'~Using the LB technique, Fendler et al.recently sand- wiched cationic magnetic Fe304 particles between the polar headgroups of arachidate ion LB films deposited on oxidized silicon substrates and also demonstrated that surfactpnt-ves- icle-incorporated Fe304 particles of diameter 50-60 A act as tiny magnets and influence the outcome of photochemical reactions, even in the absence of an externally applied magnetic field.10," Yang et al. characterized the structures of the two kinds of nanometre-sized a-Fe203-stearate alternating LB films by Fourier transform IR spectroscopy.12 Ultrafine col- loidal particles are inherently interesting since they provide information on the physical and chemical consequences of transitions between individual molecules, molecular clusters that are beginning to manifest cooperativity, and bulk mate- rial~.~~Size and/or dimensionality reduction can result in substantially altered mechanical, chemical, electrical, elec- trooptical, and magnetic properties.Indeed, investigations of semiconductor size quantization have led to the demonstration of substantially altered bandgaps and reduction p0tentia1s.l~ These facts suggest that ultrafine particles, especially in LB multilayers of magnetic ultrafine particles, should be seriously considered and studied. We have reported the polymerization of phospholipid multi- layers using the LB te~hnique.'~ In this paper, we report the preparation of new ultrafine particle multilayers, also using the LB technique.Magne+ ultrafine particles such as 1004 magnetite (Fe304), 1000 A y-diiron trioxide (y-Fe203), 70 A titanium dioxide (Ti02), and 500 A barium ferrite (BaFe,,O,,), which are used widely in cassette tape, floppy disks, and mini-floppy disks, and ultraconducting fine particle Y-Ba-Cu, were dispersed in oleic acid or stearic acid in a ballmill. The dispersed products were assembled into LB multilayers deposited onto a fresh poly(ethy1ene terephthalate) or MgO film plate. The morphology of the LB multilayers of the ultrafine particles was investigated by high-resolution trans-mission electron microscopy (TEM) and scanning electron microscopy (SEM). In addition, the obtained ultrafine particle LB multilayers were found to be X-type and to have magnetic anisotropy behaviour, observed by magnetic property measurements.Experimental lOOA Fe30, and 70A TiO, were received from Okamura Seiyu Co., Japan Fnd Toda Chemical Industry Co., Japan, respectively. 1000 A y-Fe203, 500 A BaFe12019 and Y-Ba-Cu ultraconducting fine particles were obtained from Sakai Chemistry Industry Co., Japan. Preparations of surfactant- modified ultrafine particles were carried out according to the following procedures. Uncoagulative oleic acid type 100 A Fe304 ultrafine particles Sodium carbonate (700 ml, 1.5 mol) was added dropwise to a stirred mixture of iron@) chloride (500ml, 0.5 mol) and iron(m) chloride (500ml, 0.5 mol) to afford a hydrogel. After the addition of a 5% potassium oleate solution to the hydrogel under vigorous stirring, the obtained colloids were separated by centrifugation (100 rpm) and then added to toluene (500ml) with stirring.The mixture was allowed to stand until two layers formed, then the lower layer was removed by decan- tation, and the residual colloid was washed with pure water until chloride ion was completely removed. After the toluene was removed under vacuum, the residual was crushed and dried to obtain a black powder of uncoagulative oleic acid type Fe304 ultrafine particle, (yield 66 8). Uncoagulative stearyl acid type 70 A TiOz ultrafine particles The received 70 A TiO, ultrafine particles were treated by the glass crystallization method. After the Ti02 ultrafine particles were dissolved in hydrofluoric acid and thoroughly washed with water, 5% potassium stearate was added into a ballmill.Using a procedure similar to that described for the modi$cation of Fe,O, ultrafine particles, stearyl acid type 70A Ti02 J. Mater. Chem., 1996,6(5), 691-697 691 ultrafine particles were obtained as a white uncoagulative powder Uncoagulative oleic acid type 1000 A y-Fe,03 ultrafine particles Using a procedure similar to that for Ti02, with the use of a 5% potassium oleate solution instead of a 5% potassium stearate solution, uncoagulative oleic acid type 1000 A y-Fe203 ultrafine particles were prepared Uncoagulative oleic acid type 500 A BaFel,Olg ultrafine particles This sample was prepared using a prpcedure similar to that described for the preparation of 1000 A y-Fe203 Uncoagulative oleic acid type Y-Ba-Cu ultraconducting fine particles Using a procedure similar to that for Fe304, Y-Ba-Cu ultra-conducting fine particles were mixed with 5% potassium oleate in a ballmill for 5 days at room temperature, white uncoagu- lative oleic acid type Y-Ba-Cu ultraconducting fine particles were prepared z-A isotherms and LB films TC-Aisotherms were measured using a film-balance apparatus (Model FW-2, Lauda Co ) The monolayer was characterized by using a computer-controlled film balance containing a pressure pickup system The Fe304, BaFe,,O,,, T102 and Y-Ba-Cu ultraconducting fine particles were spread from toluene, y-Fe,03 was spread from a 1 1 mixture of chloroform and benzene in concentrations of about 70 mg per 10 ml onto the water surface at 4, 20 and 40°C and at pH 7 at a speed of 61 8 cm2 min-' for 15 min The surface pressure (n)was plotted us area per repeat unit for the modified ultrafine particles The water was purified by distillation and passed through a GS-200 deionized system (Advantec Toyo Co , Ltd Japan) LB multilayers were prepared using the same film-balance apparatus mentioned above on pure aqueous subphases at 20°C using the perpendicular dipping method All the LB multilayers were deposited onto a hydrophobic poly(ethy1ene terephthalate) (PET) plate, except for Y-Ba-Cu which was deposited onto an MgO plate The plates were cleaned by ultrasonication in chloroform, washed with diethyl ether, and then rinsed with clean water several times Deposition was generally carried out at 20 mN m-', at a dipping (upstroke and downstroke) speed of 04cmmin-1 and an immersion time of 1min Between subsequent dips, the samples were allowed to dry in the air for 5 min, to avoid retransferring the last deposited monolayer to the water surface Burning away the absorbed surfactants To removeo the absorbet surfactant, 100 A Fe304, 1000 A y-Fe20,, 70 A TiO2, 500 A BaFe,,O,,, and Y-Ba-Cu fine par- ticle LB multilayers were burned at 900 "C for 5 h The change of composition for surfactant-modified ultrafine particle LB multilayers before and after being burned was investigated by attenuated total reflection (ATR)-FTIR and electron probe X-ray microanalysis (EPMA) Characterization of prepared magnetic ultrafine particle LB multila yers Transmission electron micrographs were measured for the LB multilayers of surfactant-modified ultrafine particles The modi- fied ultrafine particle LB multilayers on PET were embedded in epoxy resin (Araldite) at 60 "C for 24 h Ultrathin sections (thickness 80 nm) of the embedded specimens were obtained with an ultramicrotome (Sorvall, Model MT-6000) The sec- 692 J Muter Chem, 1996,6(5), 691-697 tions were stained with a 1 mass% aqueous solution of uranyl acetate and were examined with the aid of a high-resolution TEM (Hitachi, Model H-800) operated at an acceleration voltage of 200 kV SEM measurements on the surface of ultrafine particle LB multilayers on both PET and MgO plates were performed with a scanning electron microscope (Hitachi S-2500) ATR- IR spectroscopy for surfactant-modified ultrafine particle LB multilayers before and after being burned was performed on a Jasco Micro FT/IR-200 microsampling spectrometer over 50 scans at a resolution of 4 cm-' Magnetic susceptibility was measured at field of 11 8 kOe, sample mass 0 4 mg Results and Discussion Modification of ultrafine particles Usually, the spreading properties of ultrafine particles on the surface of water are very poor The received ultrafine particles could not be used directly to prepare the LB multilayers owing to their poor spreading properties on the surface of water To obtain uncoagulative ultrafine particles, we treated the ultrafine particles before they were used to prepare the LB multilayers (see Experimental) Fig 1 (a) shows the relationship between ultrafine particles and the physically absorbed amphiphilic molecules The hydrophilic group of oleic acid was absorbed by Fe304, so that the hydrophobic group of oleic acid was directed outwards After the ultrafine particles were modified by surfactants, their spreading behaviour in organic solvents was greatly improved, such that it was almost impossible for them to coagulate again Using these modified ultrafine particles, we could obtain n-A isotherms and LB multilayers z-A Isotherms and LB multilayers The surfactant-modified ultrafine particles formed good mono- layers on the surface of water The n-A isotherms of modified ultrafine particles were measured (at pH 7) at different temperatures Initially, monolayers of modified ultrafine particles of Fe30,, BaFe1201g, TiO2 and Y-Ba-Cu were prepared using a toluene solution of the modified ultrafine particles (cz 7 mg ml-I), and y-Fe203 was spread from a 1 1 mixture of chloroform and benzene (cz7 mg ml-'), on a subphase of water at 4, 20 and 40°C and pH 7 and their n-A isotherms were measured using a Lauda Filmbalance As an example, the isotherms of the Fe304 monolayer are shown in Fig 2 The isotherms show that a conventional linear extrapolation of the high-pressure limb of the isotherm bo zero pressure yields a limiting area of about 0 25 nm2 (25 A2) per o!eic acid molecule, equivalent to the area of a diameter ca 6 A, yhich is inconsistent with the particle diameter of Fe304 (100 A) If the magnetite is present partly on the surface of water, this will be inconsistent with the value of the surface area of one oleic acid molecule, based on the FA results This finding indicates that only surfactant molecules are present on the surface of water and magnetite is beneath the surface being held close to the surface by the attractive force of the surfactant [Fig 1(b)] Moreover, with increasing temperature, the solid monolayer decreases and an intermediate, liquid monolayer increase All of these results and phenomena of low limiting area may be due to the state of the magnetite and the absorbed surfactant Monolayers of oleic acid modified y-Fe203, BaFe,,Olg and Y-Ba-Cu were also prepared and their n-A isotherms investi- gated The results are similar to those obtained for Fe304 ?sing a similar procedure, isotherms of stearyl acid modifiFd 70 A TiOz were measured and a limiting area of about 27 A2 per stearic acid molecule was found This also indicates that stearic acid modified TiO2 ultrafine particles are under the oleic acid Fig.1 Schematic representation of the relationship between magnetic ultrafine particles and physically absorbed amphiphilic molecule. (a) 100 a Fe304 with absorbed oleic acid in toluene. (b) Distribution of Fe,04 with absorbed oleic acid on the surface of water. The hydrophilic Fe304 and the hydrophilic group of oleic acid, are implanted in the subphase, while the hydrophobic section is directed outwards.(c) Structure of LB multilayers (X-type) on a PET plate for Fe30, with absorbed oleic acid. 'O t 50 E z $40 5 v) L 30 8 s v) 20 10 n "0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 area per repeat unit/nm2 Fig. 2 n-A isotherms of oleic acid modified Fe304 at pH 7: -, 4"C; ---,20 "C; ..., 40 "C surface of the water, while the surfactant, stearic acid, is on the surface of the water. Furthermore, 4B multilayers ofsurfactant-modibfiedultrafine particlesoof 100 A Fe,O,, 1000 A y-Fe,O,, 500 A BaFeI2Ol9 and 70 A TiOz which formed stable monolayers on water could be transferred at surface pressures of 20 mNm-l onto a hydrophobic PET plate, while oleic acid modified Y-Ba-Cu could be transferred onto an MgO plate using the perpendicu-lar dipping method.The deposition ratio (deposited area/ dipped area of plate) is shown in a histogram us. the cumulative number of up and down movements of the plate (Fig. 3). The deposition ratio was obtained by recording the amount of the film consumed during the successive up and down strokes of the plate. Odd-numbered layers were deposited on the down-stroke, and even-numbered layers on the upstroke. The modi-fied ultrafine particles only deposited well on the 'downstroke' (deposition ratios ca. 85%) as shown in Fig. 3, indicating essentially X-type deposition [Fig. 1(c)]. These results may be attributable to the state of the ultrafine particles and absorbed stroke number Fig.3 Histogram showing the deposition ratio (YO)of oleic acid modified Fe30, LB multilayers us. stroke number of the plate J. Muter. Chem., 1996, 6(5),691-697 693 surfactant [Fig. 1(a), (b)]. The hydrophilic group of oleic acid was absorbed by Fe304 and the hydrophobic group was directed outwards. During the downstroke, the hydrophobic PET plate absorbed the hydrophobic group of oleic acid, so that the oleic acid modified magnetite was also absorbed onto the surface of the PET plate, while during the upstroke, it is difficult to absorb magnetite owing to the low density of oleic acid now present on the surface of the pl$e. Using a sibmilar procedure, 1000 A y-Fez03, 500 A BaFe,,O,,, 70 A TiO, and Y-Ba-Cu LB multilayers were also prepared in 8045% deposition ratios; these were also found to be X-type.Moreover, elemental analyses of cross-sections of ultrafine particle LB multilayers were carried out. Fig. 4 shows the results obtained for TiO, LB multilayers. Ti was found to be Fig. 4 Elemental analysis of the cross-section of stearic acid modified TiO, LB multilayers // HkOe Fig. 5 Magnetic hysteresis loop of oleic acid modified y-Fe203 LB multilayers 694 J. Muter. Chem., 1996, 6(5),691-697 present within the layers, indicating that ultrafine particles have been implanted in the LB multilayers. Magnetic hysteresis loop of LB multilayers During the process of preparing magnetic ultrafine particle LB multilayers, we were concerned that the strong magnetic behaviour of the particles might be lost.To investigate this, the magnetic hysteresis loops of LB multilayers of the ultrafine particle were measured (e.g. Fig. 5). The LB multilayers exhibited a rapid response to the applied magnetic field owing to the magnetic ultrafine particles, and they exhibited hysteresis between the applied magnetic field across the films. The shape of the hysteresis loop depends on the nature of the LB multilayers. The curves in Fig. 5 suggest that the obtained LB multilayers retain magnetic memory. In 105.0 I 90.0 4O00.0 3000.0 2000.0 1800.0 1600.0 1400.0 vtcm-1 Fig. 6 ATR-FTIR spectra of oleic acid modified Fe304 LB multilayers: (a)before, (b)after burning 0 100 200 300 TIK Fig.7 Temperature dependence of the magnetic susceptibility of oleic acid modified Fe304 LB multilayers Fig. 5, the saturated magnetic flux density (B,) is divided into lie on the direction of the easy magnetic axis, which is x,y (parallel to the PET plate), and z axis directions (perpen- perpendicular to the LB multilayers. dicular to the PET plate), and the angular type ratio is defined as the ratio of residual magnetic flux density (B,) to saturated magnetic flux density (B,). The angular type ratios along the Magnetic anisotropy of LB multilayers x and y axes for y-Fe203 are 0.53 and 0.51, respectively. Considering the demagnetizing field corrections (0.75 and 0.75 To further investigate the magnetic behaviour of the LB for x and y axes, respectively) owing to the random arrange- multilayers, the absorbed oleic acid or stearic acid should be ment of particles within the planes, the practical angular type completely removed from the prepared LB multilayers by ratios along the x and y axes for y-Fe,O, are both ca.0.7. burning them at 900°C for 5 h (see Experimental). These results indicate that ca. 70% of the y-Fe,O, ultrafine The ATR-FTIR spectra of Fe,O, ultrafine particle LB particles are arranged in the horizontal plane. multilayers show that absorption bands due to CH, and CH, In the case of BaFel,019, ca. 65% of the ultrafine particles at 2900 and 2840 cm-', and C=O at 1730 cm-' disappeared Table 1 Elemental analyses (in mass%) by EPMA for oleic acid modified Y-Ba-Cu ultraconducting fine particle LB multilayers (200 layers) before and after being burned before burning after burning anal ysed elements run 1 run 2 run 3 average run 1 run 2 run 3 average Y 0.559 0.512 0.49 1 0.534 0.633 0.568 0.59 1 0 597 Ba 0.546 0.522 0.570 0.546 0.742 0.790 0.790 0 774 cu 1.170 0.994 0.9 17 1.030 0.657 0.615 0.510 0.594 0 33.80 34.70 35.20 34.60 36.00 33.90 32 30 34.10 Fe 0.174 0 125 0.129 0.143 0.255 0.225 0.255 0.245 Ti 0.045 0.049 0.037 0.044 0.087 0.062 0.066 0 072 Ca 0.117 0.102 0.108 0.109 0.155 0 161 0 152 0.156 K 0.387 0.354 0.363 0.368 0.628 0.708 0 849 0 728 S1 5.830 5.680 5.770 5.760 7.530 7.470 7.450 7.480 A1 28.40 27.20 27.70 27.80 36.00 36.80 36.00 36 30 Na 0 284 0.29 1 0.249 0.275 0.470 0 561 0.801 0611 C 11.80 10.90 11 10 11.30 0.680 0 981 1100 0 920 Mg 0 437 0.399 0 390 0.409 0 722 1000 0 882 0 868 total 83 60 81.80 83 10 82.80 84.50 83.80 8 1.70 83.30 Fig.8 TEM image of a cross-sectional view of the LB multilayers for magnetic ultrafine particles with absorbed oleic acid or stearic acid on a PET plate.(a) Fe,O, imaged at 250000 magnification; (b) T10, imaged at 500W magnification; (c) y-Fe,O, imaged at 100000 magnification; (d) BaFe,,O,, imaged at 100000 magnification. J. Muter. Chem., 1996, 6(5), 691-697 695 after the LB multilayers were treated by the process of burning (Fig.6). Moreover, elemental analyses by EPMA for oleic acid modified Y-Ba-Cu ultraconducting fine particle LB multi- layers (200 layers) before and after being burned are shown in Table 1. As can be seen, Y, Ba and Cu are found to be mostly present in amounts <1 mass%, which indicates that there is virtually no Y, Ba and Cu in the LB multilayers, and therefore the obtained LB multilayers do not possess ultraconducting behaviour. Moreover, most of other elements examined were found to be present in similar amounts. The main elemental components in the LB multilayers after burning were A1 (36.3 mass%), Si (7.48) and 0 (34.1). This result may suggest that oxides were formed in the LB multilayers and the main component of the LB multilayers is A1203.Before burning, not only Y, Ba and Cu but also other elements such as A1 and Si were also found to be present. This may be due to the presence of aluminium in the ballmill used during the modifi- cation of the Y-Ba-Cu ultrafine particles. From the ultracond- ucting point of view, the oleic acid modification procedure of the ultrafine particles should be improved. Possible reasons for the total amounts of elements not equalling 100% are: (1) owing to the porous nature of Y-Ba-Cu multilayers, the strength of the X-rays is diminished; (2) the surfaces of the Y-Ba-Cu multilayers are not smooth; (3) Y-Ba-Cu multilayers may be so thin that the beam may attack the MgO plate. In addition, the carbon content of the LB multilayers has decreased from 11.3 mass% (before being burned) to 0.92 mass% (after being burned), which, together with the ATR- FTIR results, suggests that absorbed surfactant oleic acid has been removed almost completely by the burning process.After complete removal of the absorbed surfactant, the magnetic properties of the obtained LB multilayers (50 layers) were examined horizontally and perpendicular to the PET plate in the temperature range 4-300K and at a magnetic field (H,) of 11.8 kOe. In this temperature range, a magnetic susceptibility of (1-1.2) x lop3emu g-' Oe-' for Fe,O, LB multilayers was observed (Fig. 7). I represents the magnetic properties along the horizontal direction parallel to the PET plate and I1 represents those along the perpendicular direction Fig.9 SEM image for surface of oleic acid modified magnetic ultrafine particle LB multilayers (100 layers) on a PET plate, imaged at 3000 magnification. (a)y-Fe,O,; (b)BaFe,,O,, . to the PET plate. Magnetic susceptibility was observed owing to the different magnetic properties along the horizontal and perpendicular directions. This fact reveals that the films exhibit magnetic anisotropy. The value of magnetic anisotropy of the LB multilayers is only moderate, which may be attributed to the fact that the distance between ultrafine particles between the layers is only slightly greater than that between ultrafine particles within the monolayers. This may suggest that although the obtained ultrafine particle LB multilayers are X-type films [Fig.l(c)], there may be partial insertion of oleic acid between the ultrafine particles in the monolayer. Moreover, 10 Oe of coercive force (H,) for Fe304 LB multi- layers was also observed by B-H property measurements (Fig. 7). TEM studies of LB films The morphology of the LB multilayers of modified magnetite ultrafine particles was investigated by high-resolution TEM. Fig. 8 shows the micrographs of a cross-sectional view of the Fe304, TiO,, y-Fe203 and BaFe1201g LB multilayers (50 layers). The dark shapes are ultrafine particles. The TEM images of the cross-sectional view of the magnetic ultrafine Fig. 10 SEM image for surface of the oleic acid modified Y-Ba-Cu ultraconducting fine particle LB multilayers (60 layers) on an MgO plate: (a)and (c),before being burned; (b)and (d),after being burned.Imaged at 3000 magnification for (a)and (b)and loo00 magnification for (c) and (d). 696 J. Mater. Chem., 1996, 6(5), 691-697 particle LB multilayers show fine lamellar structures, especially for Ti02 and Fe,O,. In additiFn, the thickness ofTiO, LB multilayers was around lOOOA, and ca. 50-70A ultrafine particles which are the same size as Ti02 particles parallel to PET plate and in regular lines were also observed. These findings indicate that a monolayer of modified Ti02 can be transferred from a water subphase onto ordered multilayers of precise thickness by the LB deposition technique. Surface observation of ultrafine particle LB multilayers by SEM The morphology of the surfaces of X-type oleic acid modified ultrafine particles (y-Fe,O, and BaFe,,O,,) LB multilayers (100 layers) on a PET plate (Fig.9), and of the surface of X-type oleic acid modified Y-Ba-Cu ultraconducting fine particle LB multilayers (60 layers) before and after being burned (Fig. 10) were observed by SEM. Fine, uneven and lamellar surfaces were observed for LB multilayers before being burned, while, after burning, porous layer surfaces for LB multilayers were observed. Conclusion New ultrafine particle multilayers have been prepared using the Langmuir-Blodgett technique. All of the ultrafine particles were modified by oleic acid or stearic acid before being used to prepare the LB multilayers.Our results show thFt surfactant- modified magnetic ultrafin: particles of 100 A magnetite, 1000 A y-diiron trioxide, 70 A titanium dioxide, 500 A barium ferrite and ultraconducting fine particle Y-Ba-Cu form LB X- type multilayers. We also show that the obtained LB multi- layers exhibit magnetic anisotropy behaviour observed by magnetic property measurements and have fine lamellar struc- tures as observed by transmission electron microscopy. Our results also show that a high density of magnetic recording materials could be introduced into the thin films by the LB technique. Furthermore, during the process of preparing the ultrafine particle LB multilayers, if a definite magnetic field is applied, it may be possible to obtain a more regular orientation of the LB films.These new ultrafine particle LB multilayers may be useful in a wide field of applications, e.g. supermagnetic tape, audio, magnetic disk, optical sensitive materials with good ultrafine particle orientation, ultraconducting materials, electrical con- ducting materials and new functional LB materials. In addition, based on the observation of magnetite found within an intracytoplasmic membrane, it is also desirable to prepare industrial products possessing biological functions. However, some controversy still remains. For example, to further improve the magnetic behaviour of LB multilayers, how may complete control of the orientation and arrangement of magnetic materials be achieved? To improve the spreading behaviour of ultrafine particles before they are used to prepare the LB multilayers, how can the best surfactants, including polymers, be selected? And to combine ultrafine particles more efficiently, how should new surfactants containing polar groups be developed further? Moreover, from the practical application point of view, it is also necessary to further improve the mechanical strength of the LB films.We thank Mr. H. Tsuchiya of the Nitto Technical Information Center Co. for performing the TEM measurements of the LB mu1 tilayers. References 1 R. Blakemore, Science, 1975, 190, 377. 2 N. F. Borrelli, D. W. Hall, H. J. Holland and D. W. Smith, J. Appl. Phys., 1987,61, 5399. 3 E. Lifshitz, M. Yassen, L. Bykov, I. Dag and R. Chaim, J. Phys. Chem., 1994,98, 1459. 4 Y. Wang, A. Suna, W. Mahler and R. Kasowski, J. Chem. Phys., 1987,87,7315. 5 Y. Tian, C. Wu and J. H. Fendler, J. Phys. Chem., 1994,98,4913. 6 N. Herron, Y. Wang, M. M. Eddy, G. Stucky, D. E. Cox, K. Moller and T. Bein, J. Am. Chem. Soc., 1989,111,530. 7 H. Yoneyama, S. Haga and S. Yamanaka, J. Phys. Chem., 1989, 93,4833. 8 A. Jentys, R. W. Grimes, J. D. Gale and C. R. A. Catlow, J. Phys. Chem., 1993,97,13535. 9 T. Abe, Y. Tachibana, T. Uematsu and M. Twamoto, J. Chem. Soc., Chem. Commun., 1995,16,1617. 10 X. K. Zhao, S. Xu and J. H. Fendler, J. Phys. Chem., 1990,94,2573. 11 P. Herve, F. Nome and J. Fendler, J. Am. Chem. Soc., 1984, 106, 8291. 12 J. Yang, X. G. Peng, Y. Zhang, H. Wang and T. J. Li, J. Phys. Chem., 1993,97,4484. 13 J. H. Fendler, Chem. Rev., 1987,87, 877. 14 H. J. Watzke and J. H. Fendler, J. Phys. Chem., 1987,91, 854. 15 T. Nakaya, M. Yamada, K. Shibata, M. Imoto, H. Tsuchitya, M. Okuno, S. Nakaya and S. Ohno, Langmuir, 1990,6,291. Paper 5/05449D; Received 15th August, 1995 J. Matev. Chew., 1996, 6(5), 691-697 697

ISSN:0959-9428    

DOI:10.1039/JM9960600691

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Preparation and characterisation of conductive Langmuir-Blodgett films of a tetrabutylammonium-Ni (dmit), complex Leonid M. Goldenberg,".b*'Christopher Pearson,b Martin R. Bryce*' and Michael C. Petty*b ahtitUteof Chemical Physics in Chernogolovka, Russian Academy of Science, Chernogolovka, 142432 Moscow region, Russia bSchool of Engineering and Centre for Molecular Electronics, University of Durham, Durham, UK DH1 3LE 'Department of Chemistry and Centre for Molecular Electronics, University of Durham, Durham, UK DH1 3LE The behaviour of tetrabutylammonium-Ni(dmit),at the air-water interface has been investigated and Langmuir-Blodgett (LB) films have been built-up on a variety of substrates from the floating layer containing different concentrations of tricosanoic acid.The morphology, spectroscopic, electrical, electrochemical and spectroelectrochemical properties of the LB films are reported. In- plane dc room-temperature conductivity values of ort=lo-, S cm-' and thermal activation energies AE =0.08-0.1 eV over the temperature range 300-100 K, have been achieved by post-deposition electrochemical doping with four different anions, and by chemical doping with iodine vapour. The films doped with iodine and perchlorate retained this conductivity value upon storage for ca. 1 month. Electrochemical doping during deposition of the LB films resulted in conductivity values of ort=lov3S cm-'. The Langmuir-Blodgett (LB) technique is now recognised as an important method for organising charge-transfer complexes at the molecular level.' Many of the materials studied are amphiphilic systems containing the electron acceptor tetracy- ano-p-quinodimethane (TCNQ)2-4 or the electron donor tetra- thiafulvalene (TTF) and its close analog~es.~-~ The LB films of these materials are characterised by strong one-dimensional interactions and the most highly conducting layers possess in- plane conductivity values in the range art= 10-,-1 S cm-' after doping with iodine vapour.Over the last decade, work on crystalline molecular conductors has established that many cation salts of M(dmit), anions [M=Ni, Pd, Pt, Au; dmit= bis(4,5-dimercapto-l,3-dithiole-2-thione)] exhibit metallic behaviour, and superconductivity has been observed in a few salts.' The presence of peripheral sulfur atoms in the M(dmit), anions, which engage in non-bonded S---S interactions, facili- tates an increase in the dimensionality of the system, thereby stabilising the metallic state.In the search for LB films of charge-transfer systems with higher dimensionality, Japanese workers have prepared thin films of tetraalkylammonium M(dmit), complexes (M =Au, Ni, Pd or Pt) by attaching long hydrophobic chains to the cation; conductivity values of 10-3-50 S cm-' were obtained after chemical or electrochemi- cal doping, assuming a thickness per layer of 3 nm." Because of the unstable nature of the condensed films of these materials at the air-water interface, the complexes were usually deposited as 1 :1 mixtures with a fatty acid using the horizontal touching technique."*12 Monolayer formation of related amphiphilic tetraalkylammonium M(dmit), complexes (M =Pt, Pd upon storage for at least several months at room temperature.We have used LB films of the 1 : 1 stoichiometry complex as the basis of a thin-film transistor21 and as a charge-injection layer in an electroluminescent device.,, Recently, we have succeeded in depositing stable LB mono- layer and multilayer films of some non-amphiphilic charge- transfer materials, e.g. ethylenedithio-TTF (EDT-TTF) deriva- tives with aryl substituents using only 25% molar fatty acid as additive,23 and a TTF derivative containing an azobenzene substituent without addition of any fatty We also have been able to deposit reproducibly multilayer films of pure bis(ethy1enedithio)TTF (BEDT-TTF) with no added fatty These res~lts,~-,~ demonstrate for the first time that for some charge-transfer systems the presence of a traditional long-chain substituent is not necessary for the formation of LB films.This finding is an important development, as the attachment of a long chain can often present difficulties in synthesis and, more especially, in the purification of the material. In this context, we decided to explore the LB film behaviour of the commercially available dmit salt Bu4N-Ni(dmit), 1, which does not contain a long hydro- phobic chain. Herein we report film formation of complex 1 using the LB and Ni) has been reported by Taylor and co-~orkers.~~-~~ technique, and the electrical, electrochemical and spectroscopic We have previously reported LB films of (N-o~tadecylpyridinium)~-Ni(dmit),with in-plane conductivity values following iodine d~ping'~,~~ as high as ort=0.9 S cm-', while films of the analogous 1: 1 salt N-octadecyl-pyridinium-Ni(dmit), possess lower conductivity val~es,'~ ort=0.2S cm-'.For the latter salt, similar conductivity values were obtained by electrochemical doping.,' In the case of films of the 1 :1 salt, high conductivity values were observed only when aggregates of micrometre dimensions were formed." Films of both complexes (N-octadecylpyridinium),-Ni(dmit), salts (x=1 or 2) were obtained without the need for added fatty acid, and in contrast to most LB films of charge- transfer materials,' they retained their high conductivity values studies of conducting films obtained by electrochemical and chemical doping.Experimenta1 Complex 1 was obtained from Tokyo Kasei Organic Chemicals and used as received. Tricosanoic acid (TA) was obtained from Sigma. LB film deposition was undertaken in a class 10000 micro- electronics clean room using constant-perimeter barrier LB troughs designed and built in Durham.26 The solution of 1 in dichloromethane (0.5 g dmP3) and TA in chloroform (1 g dm -3) were used for preparation of spreading solutions. The J. Muter. Chem., 1996,6( 5), 699-704 699 solution was spread onto the surface of ultrapure water (obtained by reverse osmosis, deionisation and ultraviolet sterilisation) at pH 5 8 k0 2 at 20 f2 "C The pressure us area isotherms were measured at a compression rate of approxi- mately 4 x nm2 complex-' s-' LB films were built up on glass, indium tin oxide glass (ITO, sheet resistance 300R per square, from Balzers) and glass slides coated with Au Au electrodes on glass were obtained by vacuum deposition of 30-35nm of Au undercoated with 3-5nm of Cr to improve adhesion of Au to the glass The glass was cleaned by ultrasonic cleaning in a 5% solution of Decon 90 for 30 min, rinsing in ultrapure water and drying in a stream of nitrogen For IT0 and Au-coated glass, the above procedure was adopted first and then, to improve the hydro- philic properties, these substrates were treated prior to LB transfer with saturated Na2Cr20,-conc H2S04 solution for ca 10s and carefully washed with ultrapure water 27 Film thicknesses were measured using a surface-profiling Tencor Instruments Alpha-Step 200 (stylus force = 11& 1 mg) A layer of aluminium (thickness ca 150 nm) was evaporated over the step between the organic layer and the uncoated substrate The film morphology was investigated using a scanning elec- tron microscope operating at 20 kV Optical absorption spectra were recorded for films deposited onto glass using a Perkin- Elmer Lambda 19 UV-VIS-NIR spectrometer For electro- chemistry, IT0 slides with an area of between 20 and 30 cm2 were used for LB film transfer After film deposition, the slides were carefully cut with a diamond-tipped stylus to form several electrodes with contact areas of 0 1-0 5 cm2 We have devel- oped a technique for the production of gold electrode arrays with narrow gaps without the need for photolithography a glass slide was first coated with a film of gold by thermal evaporation, several parallel lines were then scribed in this gold film using the tip of a new single-edge industrial razor blade This method produced gaps in the gold film of width cu 30pm which could be coated subsequently with an LB film Interdigitated Au electrodes with a gap of 20 pm were prepared by photolithography An EG&G PARC model 273 potentiostat with an Advanced Bryans X Y recorder was used for electrochemical experiments Pt mesh served as the counter electrode and IT0 or Au electrodes covered with LB films served as working electrodes All potentials were recorded us an Ag/AgCl reference electrode LiClO, (Fluka, microselect), KC1 (Fluka, microselect), Bu,NBr (Aldrich), KI (Hopkin & Williams), NaC10, (Aldrich) and ultrapure water were used for the preparation of electrolyte solutions Spectroelectrochemistry was undertaken using the Lamba 19 spectrophotometer described above with a Ministat (Thomson Electrochem Ltd, Newcastle upon Tyne, UK) A spectroelectrochemical cell was based on a cuvette of thickness 1 cm, Pt wire was used as the counter electrode, while Ag wire served as a quasi-reference Chemical doping of the LB films was achieved by exposure to iodine vapour in a sealed container In-plane dc conductivity studies were undertaken using a two-probe technique The electrical contacts were either a carbon cement (Neubauer Chemicallien) on glass or, as described above, Au electrodes with gap 30 pm The conductivity normal to the film surface was measured by using evaporated Au top contact dots with diameter 0 1 cm for the films deposited on Au-coated glass slides Room-temperature measurements were undertaken in a screened sample chamber, evacuated to a pressure of ca mbar using a rotary pump Electrical conductivity measurements over the temperature range 100-300 K were made in helium using an Oxford Instruments DN704 exchange gas cryostat The voltage source in these experiments was a Time Instruments voltage calibrator and the current was monitored using a Keithley picoammeter Electrochemical doping during LB film transfer was achieved at a constant current of 3-6 pA supplied from a Farnell Instruments current 700 J Muter Chew , 1996, 6(5), 699-704 -k ',i 0 0 0 10 0 20 030 molecular area/nm* Fig.1 Pressure us area isotherms of 1 mixed with different concen- trations of TA Subphase pH 5 8 +O 2, temperature 20+2 "C, mono-layer compression rate ca 4 x 10 nm2 complex ' s ' a, 0% TA, b, 24% TA, C,66% TA source between a moving (vertical dipping) Au array electrode and another Au counter electrode placed in the subphase outside the barrier In another version of this experiment the counter electrode was attached to the working electrode and the two were dipped together For these experiments a 0 1 mol dm-3 KI or NaC10, subphase was used Results and Discussion LB film preparation and morphology Condensed pressure us area isotherms could be obtained for floating films of pure 1, or for 1 mixed with TA Fig 1 shows examples for the pure complex, and for two different concen- trations of the mixture with TA The isotherms were reproduc- ible (within 5YO)for subsequent expansions and compressions It is noteworthy that the isotherms were independent of the time that the film was left on the subphase before compression, this contrasts markedly with results reported by Taylor et a1 l4 and our~elves'~ for amphiphilic Ni(dmit), analogues Here, true monolayers of some systems were obtained only if the floating film was kept for several hours on the subphase in its uncompressed state The average molecular area per complex 1 can be calculated by extrapolating the high-pressure regions of the isotherms (>30 mN m-') in Fig 1 to zero pressure and subtracting the average area occupied by the fatty acid molecules (assuming the TA molecules are all in contact with the subphase surface and have a cross-sectional area of 0 20 nm2) Fig 2 shows the resulting dependence upon fatty acid concentration The Ni(dmit), moiety may be modelled by a box of dimensions of 161 nm x 0 623 nm x 0 366 nm', while the tetrabutylam-monium cation will be more similar to a sphere of approximate diameter 13 nm At low TA concentrations, Fig 2 indicates 0 20 0 I cuFE016/. I I 000 ' 1 0 20 40 60 80 100 concentration of TA(%) Fig. 2 Area per complex, calculated assuming the cross-section of TA as 0 2 nm2 (see text for details) us concentration of TA Subphase pH 5 8 & 0 2, temperature 20 f2 "C, monolayer compression rate ca 4x 10 ' nm2 complex ' s ' \ 16 b A 37 12 Ak A3E AAY 245 0 20 40 60 80 100 concentration of TA(%) Fig.3 Single layer thickness of films of 1 determined by Alpha-Step profiling us.concentration of TA that the organometallic complex is almost certainly in the form of a multilayer on the water surface. As the proportion of fatty acid increases, the average molecular area per complex also increases, indicating that more of the Ni(dmit), molecules and/or the counter ions are incorporated in the fatty acid monolayer. LB film deposition was undertaken at a surface pressure of 30-35 mN m-'. Pure 1 exhibited Z-type deposition.For mixtures with fatty acid, the film transfer started as Z-type deposition but this reverted to Y-type after several (1-4, depending on the exact composition) dipping cycles. The deposition ratio was 1.OkO.1 for both the Z and the Y cycles. Multilayers assembled from pure 1 appeared reasonably uni- form to the eye but their quality improved with increasing fatty acid content. A plot of the average thickness per layer, measured with the surface profiling Alpha-Step, vs. TA concentration is shown in Fig. 3. The large values of thickness obtained with low fatty acid concentrations confirm the suggestion above that the floating film is more than one molecule (complex) in thickness.With increasing content of TA, the average thickness per transferred layer decreases and approaches a constant value of 5 nm. This is considerably greater than the longest side of the Ni(dmit), anion (1.61 nm) but is consistent with a film in which the Ni(dmit), anion is mixed within the fatty acid matrix (thickness 3.0 nm) and the tetrabutylammonium cation is on the top. This would give a total thickness of ca. 3.0 nm + 1.3 nm =4.3 nm. This model results in the calculated average area per complex to equal that of the Ni(dmit), cross- section (ca. 0.23 nm2), which corresponds well with the observed value of 0.18 nm2 at high concentrations of TA (Fig.1). The LB films of 1 were studied using scanning electron microscopy (SEM). Fig. 4 shows the electron micrograph of a 26-layer LB film of 1containing 44% TA (note that at this TA concentration, the mixed LB films are still electrically conduc- tive, see Fig. 6 later). The film consists of two phases, with lighter aggregates randomly distributed in a darker matrix. The dimension of the aggregates is < 1 pm, which is consider- ably smaller than the aggregates previously observed for LB films of the amphiphilic We suggest that the LB films of 1 contain separated phases of the Ni(dmit), complex and TA well distributed in each other. As the film is conductive, the dark regions are likely to consist of the organometallic species.Optical absorption Fig. 5(u) shows the optical absorption for LB films of 1mixed with 38 mol% of TA for different numbers of layers. Absorption bands are observed at ca. 1350, 1150, 650, 600, 460, 400, 360 and 320 nm. These are associated with electronic transitions within the Ni(dmit), moietiesz8 and are similar to the bands observed for the LB films of N-octadecyl-Fig. 4 Scanning electron micrograph for a 26-layer LB film of 1 mixed with 44 mol% of TA deposited on Au, after iodine doping and vacuum treatment 3.5 3 2.5 2 1.5 1 h .-Y 0.5 t3 0 nY5 300 800 1300 1800 v 1.52l 300 800 1300 I800 wavelengthhm Fig.5 Optical absorption of LB films of 1 mixed with 38 mol% of TA deposited on glass: (a) dependence of absorption on the number of layers for as-deposited films (inset shows the plot of absorbance at 1150 nm us.the number of layers); (b) effect of iodine doping and vacuum treatment for a 38-layer LB film: -, as deposited; ---, iodine doped; ---, after vacuum treatment (high conductivity state) pyridinium-Ni(dmit),.19 The insert in Fig. 5(a)shows that the plot of absorbance at 1150 nm us. the number of layers is linear, indicating reproducible deposition of the LB layers. Fig. 5(b) shows the evolution of the optical absorption spec- trum after doping a 38-layer film with iodine vapour. Immediately after doping, the peaks at 1350 and 1150nm disappeared and a new peak was evident at 920nm.As the film was treated in vacuum to gain the maximum conductivity value (see below) the intensity of the peak at 920 nm decreased. J. Muter. Chern., 1996, 6(5),699-704 701 This absorption is associated with the formation of a mixed-valence state Electrochemistry and spectroelectrochemistry The electrochemical response for LB films of 1 built up from floating layers with 24% TA was found to be similar in different electrolytes Fig 6 shows the response in Bu,NBr and KCl electrolytes Redox potential data obtained using four electrolytes are collated in Table 1 Both NilI1+NiIV (Fig 6, couple A) and NiI1-+Ni1I1(couple B) redox transitions within the dmit ligand were observed at potentials similar to those found previously for an amphiphilic derivative2' and the results are consistent with solution studies on other Ni(dmit), com-plexes 29 We also measured the voltammetric response for multilayer films of 1 and it was found to be similar to the single-layer response Moreover, the electroactivity increased with increasing number of layers as shown in Fig 7, where the reduction peak currents are plotted us the (number of layers) x (transfer ratio) This suggests that all layers in the multilayer assembly participate in the electrochemical activity These data indicate that the redox processes in these films are quite facile and are not hindered by counter ion diffusion This result forms a good basis for studies on electrochemical doping Fig 8 shows the results of spectroelectrochemical studies in two Bu,NBr and KI electrolyte solutions An optical change was observed after applying a potential step for only a few minutes This contrasts with the several hours required before a response was obtained from more compact LB films of an A b 05 VA B Fig.6 Cyclic voltammogram of a single LB layer of 1 mixed with 24 mol% of TA deposited on an IT0 electrode (a) 3 rnol dm KCl solution, scan rate 0 05 V s ',(b) 0 5 rnol dm Bu,NBr solution, scan rate 0 05 V s Table 1 Redox potentials, determined by cyclic voltammetry, for a single layer of complex 1 mixed with 24mol% TA in different electrolyte solutions electrolyte solution (concentration/mol dm 3, E,"/V E,"/V KC1 (3) -008 +036 LiClO, (0 4) -026 +014 KI (1) -028 +016* Bu,NBr (0 5) -018 +027 ~~~ "Determined as midpoint between the cathodic and anodic peaks bReduction peak potential, as the oxidation peak was not observed due to the rising background current 702 J Muter Chew , 1996,6(5), 699-704 20 I 0 16 A%I0 12 A 4.9 A 0 3 6 9 12 15 (no of layers) x (transferratio) Fig.7 Reduction peak currents measured during cyclic voltammetry of LB layers of 1 mixed with 24 mol% of TA deposited on an IT0 electrode in 3 mol dm KC1 solution, scan rate 0 05 V s us (number of layers) x (transfer ratio) 0,first cathodic peak, A second cathodic peak 01. I I. 1, I I I I. I .'.'I I. v 350 650 950 1250 350 575 800 1025 1250 wavelengthhm Fig.8 Absorption spectra for a 19-layer LB film of 1 mixed with 40 mol% of TA deposited on IT0 Measurements at different potentials us Ag wire (a) 05 mol dm Bu,NBr solution (-, open circuit, ___ , + 1 V, ---, -0 3 V), (b) 1 mol dm KI solution (-, open circuit, ---, +06V, -, -03V) amphiphilic TTF derivative studied previously 30 In accord with the spectroscopic changes accompanying chemical doping of LB films of 1, electrochemical oxidation resulted in the disappearance of a peak at 1150 nm and the emergence of a new peak at ca 900nm On changing the potential to reduction, the spectrum reverted to that measured previously In-plane electrical conductivity The in-plane dc conductivities for the as-deposited LB films of pure 1 or for samples mixed with TA were generally <10 'S cm-' However, after doping with iodine vapour the conductivity increased almost immediately, and continued to grow after the application of vacuum Maximum conductivity values in the range art= 10-3-10-2 S cm-' were achieved after ca.20 min storage under vacuum. These values were calculated using the measured film thickness, which depended on the concentration of TA (Fig. 3). The conductivity for complex 1 is, therefore, ca. one order of magnitude lower than that recently reported for the 1 :1 N-octadecylpyridinium deriva- tive.lg Fig. 9 shows the dependence of the in-plane room-temperature dc conductivity for iodine-doped samples of 1 on the concentration of TA. This plot indicates that percolation threshold is achieved at a TA concentration of ca.50%. For electrochemical doping experiments, multilayer films were built-up on Au electrodes with a 30 pm gap from a floating layer with a different concentration of TA. The films were oxidised either at a constant potential of 0.6-0.9 V or at a constant current of ca. 1-2 PA. The process was terminated from time to time, the films were washed with water and dried in a nitrogen steam and the conductivity was measured. Conductivity values achieved in different electrolytes, and by iodine-vapour doping, are collated in Table 2. We have also measured the conductivity normal to the film surface for iodine-doped samples and samples doped electrochemically in 3 mol dm-3 KCl. This conductivity was the same order of magnitude as the in-plane conductivity.In contrast to the usual method of post-deposition doping, Tieke et aL3' suggested the technique of electrochemical oxi- dation with a 'live' electrode during LB film deposition, and this method was subsequently used by Morand et al.32 However, neither group reported conductivity data on the films obtained using this approach. We have now applied this technique to LB films of complex 1, using constant current oxidation and a 0.1 mol dm-3 KI or NaC10, subphase. The in-plane conductivity of the resulting LB films was crt= S cm-l, which is similar to the values discussed above obtained from post-deposition oxidation. To our knowledge, this is the first time that conductivity data have been measured as a result of electrochemical doping during LB film deposition.We monitored the conductivity of different samples with time in order to estimate the stability of the conducting films. 10-* I 0 1044 0 20 40 60 80 100 concentrationof TA(%) Fig. 9 Plot of in-plane dc conductivity measured at room temperature for iodine-doped samples of LB films of 1 deposited on an Au electrode with a 30 pm gap us. concentration of TA Table 2 Room-temperature dc in-plane conductivity values for the multilayer films (15-30 layers) of 1 mixed with 24-44% TA, obtained by electrochemical doping in different electrolytes, and by iodine- vapour doping (unless specified otherwise data were obtained on a gold electrode with a 30 pm gap) electrolyte conductivity/ concentration of TA (concentration/mol dmW3) S cm-l (mol%) ~ ~~ KC1 (3) (0.3-1) x 24-35 LiC10, (0.4) (0.7-1) x 10-3 24-35 Bu,NBr (0.5) (0.7-2) x 10-3 24-35 (0.5-1) x 10-3 24-35 (0.3-7) x 10-3 24-44 (0.2-8) x lop2 24-44 "For carbon cement contacts onto glass.0I 0-la 5n 0.002 0.006 0.010 0.0145-c -14 tv-18 L 0 0 1...1...1...1. .. I... 0.002 0.006 0.010 0.014 T /K Fig. 10 Current us. reciprocal temperature for a 24-layer LB film of 1 mixed with 24 mol% of TA deposited on an Au electrode with a 30 pm gap, applied voltage 1 V: (a)after electrochemical doping in 0.4 mol dm-3 LiC10, electrolyte; (b) after iodine doping. AE is the thermal activation energy; 0,decreasing temperature; 0,increasing temperature The general conclusion is that samples doped with iodine vapour were stable (either with carbon or Au contacts) and the conductivity decreased only slightly over one month.The same behaviour was observed for samples doped electrochemi- cally in LiC10, or KI solutions. On the other hand, samples doped in Bu,NBr solution showed less reproducible behaviour, although some samples showed reasonable stability of the conductivity value for one month. Less stable were samples doped electrochemically in KCl solution, for which a drop in conductivity of 1-2 orders of magnitude occurred after one month. The temperature dependences over the range 300-100 K of the in-plane electrical conductivity for the LB films doped electrochemically with perchlorate and chemically with iodine, obtained in the same deposition experiment, are shown in Fig.10. In both cases, the conductivity followed an exponential dependence upon temperature, with thermal activation energies AE =0.1 and 0.08 eV, respectively. These values are similar to those obtained for the films of other amphiphilic Ni(dmit), complexes doped with iodine (0.05-0.06 eV)" or electrochemi- cally (0.07 eV).20 The results presented in this paper (e.g. variable deposition ratio) suggest that LB films of 1 are not as ordered as those built up from amphiphilic organometallic compounds. We have, therefore, undertaken some experiments using films of 1 produced by solution casting. Layers were deposited from a chloroform solution (1 g dm-3).The thickness of the resulting films was ca. 120nm (measured by Alpha-Step) and, after iodine doping, the in-plane dc room-temperature conductivity was 1x loF2S cm-'. This result confirms the presence of considerable disorder of the Ni(dmit), moieties within the LB films. J. Muter. Chem., 1996, 6(5), 699-704 703 Conclusions H Tachibana, M Tanaka and Y Kawabata, Thin Solid Films, 1989,179,183 We have reported the preparation and characterisation of LB films of Bu,N-Ni(dmit), 1 mixed with TA LB films were reproducibly built up from the floating layer containing differ- ent concentrations of TA and they were conductive after chemical or electrochemical doping with TA concentrations of 11 12 Y F Miura, M Takenaga, A Kasai, T Nakamura, Y Nishio, M Matsumoto and Y Kawabata, Thin Solid Films, 1992, 210/211,306 Y F Miura, M Takenaga, A Kasai, T Nakamura, M Matsumoto and Y Kawabata, Jpn J Appl Phys, 1991, 30, 3503 up to 50% Cyclic voltammetry and spectroelectrochemistry for LB films of complex 1 revealed a facile response for both monolayer and multilayer films Chemical doping by iodine vapour and electrochemical doping of the LB multilayers by different anions resulted in a maximum room-temperature dc in-plane conductivity of ca 1 x lo-, S cm-I The temperature 13 14 15 16 D M Taylor, A E Underhill, S K Gupta and C E Wainwright, Makromol Chem ,Macromol Symp, 1991,46, 199 D M Taylor, S K Gupta, A E Underhill and C E Wainwright, Thin Solid Films, 1992, 210/211,287 S K Gupta, D M Taylor, P Dynarowicz, E Barlow, C E Wainwright and A E Underhill, Langmuir, 1992,8,3057 S K Gupta, D M Taylor, A E Underhill and C E Wainwright, dependence of conductivity over the range 300-100 K was found to be similar for both the electrochemically and the chemically doped films 17 18 Synth Met, 1993,58,373 A S Dhindsa, J P Badyal, C Pearson, M R Bryce and M C Petty, J Chem Soc Chem Commun, 1991,322 C Pearson, A S Dhindsa, M C Petty and M R Bryce, Thin Solid L M G thanks the University of Durham for financial support M R B thanks the University of Durham for a Sir Derman 19 Films, 1992,210/211,257 C Pearson, A S Dhindsa, L M Goldenberg, R A Singh, R Dieing, A J Moore, M R Bryce and M C Petty, J Muter Christopherson Research Fellowship We thank Professor P Delhaes for suggestions concerning electrochemical doping during film deposition 20 21 Chem, 1995,5,1610 L M Goldenberg, A P Monkman, C Pearson, J Gibson, M R Bryce and M C Petty, Thin Solid Films, 1996, in press C Pearson, J E Gibson, A J Moore, M R Bryce and M C Petty, Electron Lett, 1993,29, 1377 References 22 G Williams, A J Moore, M R Bryce and M C Petty, Thin Solid Films, 1994,244,936 1 Reviews T Nakamura and K Kawabata, Techno Japan, 1989,22, 8, B Tieke, Adv Muter, 1990,2,222,M R Bryce and M C Petty, Nature, 1995,374,771 A Barraud, A Raudel-Teixier, M Vandevyver and P Lesieur, Nouv J Chem ,1985,9,365 T Nakamura, M Matsumoto, F Takei, M Tanaka, T Sekiguchi, E Manda and Y Kawabata, Chem Lett, 1986,709 A S Dhindsa, G H Davies, M R Bryce, J Yarwood, J P Lloyd, M C Petty and Y M Lvov, J Mol Electron, 1989,5,135 J Richard, M Vandevyver, A Barraud, J P Morand, R Lapouyade, P Delhaes, J F Jacquinot and M Roulhay, J Chem Soc Chem Commun, 1988,754 C Dourthe, M Izumi, C Garrigou-Lagrange, T Buffeteau, P Desbat and P Delhaes, J Phys Chem ,1992,96,2812 A S Dhindsa, Y P Song, J P Badyal, M R Bryce, Y M Lvov, M C Petty and J Yarwood, Chem Muter, 1992,4,724 L M Goldenberg, R Andreu, M Saviron, A J Moore, J Garin, M R Bryce and M C Petty, J Mater Chem, 1995,5, 1593 Reviews M R Bryce, Chem Soc Rev, 1991, 20, 355, A E Underhill, J Mater Chem, 1992, 2, 1, P Cassoux and L Valade, in Inorganic Materials, ed D W Bruce and D O’Hare, 23 24 25 26 27 28 29 30 31 32 L M Goldenberg, J Y Becker, 0 Paz-Tal Levi, V Y Khodorkovsky, M R Bryce and M C Petty, J Chem SOC Chem Commun ,1995,475 L M Goldenberg, S Wegener, M C Petty and M R Bryce, unpublished results L M Goldenberg, C Pearson, M R Bryce and M C Petty, manuscnpt in preparation M C Petty and W A Barlow, in Langmuir-Blodgett Films, ed G G Roberts, Plenum Press, New York, 1990, p 93 Y Fu, J Ouyang and A B P Lever, J Phys Chem, 1993, 97, 12753 G Steimecke, H -J Sieler, R Kirmse and E Hoyer, Phosphorus Sulfur, 1979,7,49 J-B Tommasino, B Pomarede, D Medus, D de Mantauzon and P Cassoux, Mol Cryst Liq Cryst, 1993,237,445 L M Goldenberg, G Cooke, C Pearson, A P Monkman, M R Bryce and M C Petty, Thin Solid Films, 1994,238,280 B Tieke, A Wegmann, W Fischer, B Hilti, C W Mayer and J Pfeiffer, Thin Solid Films, 1989,179, 233 J P Morand, L Brzezinski and M C Lopez, Thin Solid Films, 1992,210/211,280 10 Wiley, Chichester, 1992,ch 1 T Nakamura, H Tanaka, K KOJima, M Matsumoto, Paper 5/07323F, Received 7th November, 1995 704 J Mater Chew , 1996, 6(5), 699-704

ISSN:0959-9428    

DOI:10.1039/JM9960600699

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

~~~ Laser photolytic studies of sensitizers for negative photoresists: 2,7-diazidofluorene in poly(methy1 methacrylate) films Tsutomu Yamamoto,' Hiroshi Miyasaka,' Akira Itaya,*'" Minoru Toriumib and Takumi Uenob 'Department of Polymer Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606, Japan bCentral Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo 185, Japan The time evolution of the transient absorption spectra of 2,7-diazidofluorene (DAF) (N, -R-N,) under excimer laser irradiation has been investigated in poly(methy1 methacrylate) (PMMA) films and in inert cyclohexane solution and compared with the results for 4,4'-diazido-3,3'-dimethoxybiphenyl(DADMB), which has a similar biphenyl skeleton to DAF. The results from a DAF-cyclohexane solution containing diethylamine indicated that, in addition to the triplet azido nitrene (:N-R-N,) which was the main intermediate, didehydroazepine derivatives were generated.The formation of these intermediates in solution and in PMMA films was completed within the duration of the laser pulse. The reaction of these intermediates in solution was completed within 10 ms and in PMMA films within 100 s, while the reaction related to the azido nitrene of DADMB in PMMA films continued up to 1200 s. The results for 1YOw/w DAF-doped PMMA films irradiated with a high fluence indicated that the azido nitrene and the dinitrene (:N-R-N:) underwent dimerization and/or further polymerization, suggesting that DAF molecules form aggregates even in dilute PMMA films ( 1YOw/w).The difference in the miscibility of DAF and DADMB in PMMA affected the photoreaction behaviour of these diazido compounds in polymer films. The photochemical reaction behaviour of aromatic azides and their nitrenes are of great importance not only for organic synthesis but also for photolithographic applications in the formation of negative images. The primary processes in the photodecomposition of aromatic azides in solution have been investigated by laser flash photolysis.'-1° To reveal the litho- graphic behaviour of the compounds, however, information on the photochemical reaction mechanism of the compounds in polymer matrices is indispensable. Since the motion of molecules in polymer matrices is highly suppressed compared with that in solution, special features may appear in photo- chemical reactions of aromatic azides and their nitrenes in polymer matrices. In addition, from a viewpoint of photo- lithographic applications, aromatic diazides are much more important than monoazides.1',12 Studies on the primary photo- chemical processes of aromatic diazides by laser flash photoly- sis are few, although the primary photochemical process of 4,4'-diazidobiphenyl in cyclohexane solution has been reported.' Recently, we investigated the photochemical behaviour of 4,4'-diazido-3,3'-dimethoxybiphenyl(DADMB, l),an aromatic diazide, which has two equivalent azide groups, in poly(methy1 methacrylate) (PMMA) films and in cyclohexane solution by laser flash photolysis and revealed that DADMB has a quite different photochemical behaviour from normal aromatic azide compounds (Ar-N,)." For example, photolysis of phenyl azide (Ph-N,), which is a typical aromatic azide, generates singlet nitrene (Ph' -N).',T'~The singlet nitrene undergoes intersystem crossing to the triplet nitrene (Ph3 -N), which produces azo-compounds by dimerization in inert solvents such as cyclohexane, in competition with the ring expansion to result in the formation of didehydroazepine derivatives.Photolysis of DADMB in cyclohexane, however, never gave didehydroazepine derivatives, but only the triplet azido nitrene (N, -R'-N:). Hence, DADMB is one of the few compounds that do not give didehydroazepine derivatives.In addition, a related reaction of the azido nitrene in PMMA films continued up to 1200s, and laser irradiation with a high fluence gave the dinitrene (:N-R'-N) in cyclohexane solution and in PMMA films. (Na-R'-N3) DADMB 1 2,7-Diazidofluorene (DAF, 2), one of the diazidobiphenyl derivatives which was developed as a negative resist photosensi- tive compound for i-line phase-shifting lithography,12 has two equivalent azide groups in each molecule and a similar biphenyl skeleton to DADMB. The product (~4)of the molar absorption coefficient E at the i-line (365 nm) and the production quantum yield q5 of the nitrene produced by azide photodecomposition for DAF in a m,p-cresol novolak resin was the largest among the several diazidobiphenyl derivatives examined, and DAF gave the highest resist sensitivity for the i-line.12 The $J value for DAF was almost the same as that for DADMB, and nitrenes produced from these diazides had the same reactivity with the novolak resin." In addition, the novolac resist using a mixture of DAF and DADMB gave a high resolution pattern.In a study on the photodecomposition processes of diazide compounds, it is difficult to isolate the azido nitrene intermedi- ate because it is photoreactive. In addition, for reactions in polymer matrices, isolation of the intermediates is also quite difficult because of their complicated reactions with polymers. Hence the use of time-resolved spectroscopic methods is con- venient for investigating photodecomposition processes of diaz- ide compounds.In the present work, using an excimer laser, we have investigated the photoreaction mechanism of DAF in PMMA films and in inert cyclohexane solution by means of time-resolved absorption spectroscopy and compared the mechanisms with those of DADMB. Experimental DAF was the same as used previously12 and was used after recrystallization. Diethylamine (DEA; HNEt,) was distilled under a reduced pressure of N2 gas. PMMA was the same as used previously." PMMA films doped with 1% w/w and 10% w/w DAF relative to the polymer were prepared by solvent J. Muter. Chem., 1996, 6(5), 705-710 705 casting on quartz plates from benzene and by spin coating from toluene, respectively The films were dned under vacuum for more than 8 h The film thickness was adjusted to obtain an absorbance of 1-1 5 at the excitation wavelength (308 nm) A microcomputer-controlled laser flash photolysis system for measuring transient absorption spectra was the same as that used before lo The excitation source was an XeCl excimer laser (Lumonics EX-510, A =308 nm, pulse duration = 12 ns) Samples were replaced after each excitation Results and Discussion Photodecomposition of DAF in rigid glasses at 77 K In order to investigate the shapes of the absorption spectra of azido nitrene (N, -R-N.) and dinitrene (:N-R-N) pro-duced from DAF, we performed photolysis of DAF in a rigid matrix of methylcyclohexane-isopentane at 77 K using a laser with a low fluence as the irradiation source The scheme of the reaction induced by repetitive irradiation under the present conditions is as follows N,-R-N,+ N,-R-N-+:N-R-N Fig 1 shows the change in the absorption spectrum of DAF induced by laser irradiation with a low fluence of 0 49 mJ cm-' The spectrum around 350 nm observed on a single shot is assigned to the triplet azido nitrene (N3-R -N), 2-azido-7-nitrenofluorene The spectrum with peaks at cu 410, 390 and 370nm observed on 1800 shots is assigned to the dinitrene (:N-R-N:), 2,7-dinitrenofluorene, since diazide compounds are known to be converted into the dinitrene ozu the azido nitrene intermediate in a rigid matrix at 77 K l5l6 The result of the resolution of the spectra into three components showed that the spectrum attained at 50 shots of the laser excitation indicates the maximum concen- tration of the intermediate, azido nitrene, under the present experimental conditions The intensity change in the weak absorption of the peaks at 525 and 572nm with an increase in the number of laser shots was in agreement with that of the azido nitrene at 350 nm, indicating that these absorptions are also due to the triplet azido nitrene, although the absorption was not clearly observed for the spectrum on a single laser shot because of the weak intensity compared with that at 350 nm 1 1 1 z C 'I -I #" nnl(A400 500 600 wavelengthhm Fig.1 Changes in the absorption spectra of 3 3 x 10 mol dm DAF in a ngd matrix of methylcyclohexane-isopentane at 77 K induced by laser irradiation Laser fluence 0 49 mJ cm Number of laser shots (a) 1, (4 3, (4 6, (4 10, (415, (f)20, k)30, (h) 50, (11 100, (1) 150,(k)600 and (1) 1800 706 J Muter Chem , 1996, 6(5), 705-710 We noticed that the absorption spectrum of the triplet azido nitrene created from DAF was similar to that from DADMB except for the bands around 525 and 572nm in the longer wavelength region, while the absorption spectrum of the dini- trene created from DAF was quite different from that from DADMB lo Concerning the latter observation, the results on 4,4'-diazidobiphenyl in an organic glassy solvent at 70 K16 suggest the presence of two structures for the dinitrene created from DADMB a twisted biphenyl skeleton and a quinonoid structure The interaction between the two nitreno groups in the former structure was negligible The absorption spectrum of the twisted structure has been reported to be observed, while the spectrum of the quinonoid structure was not ident- ified because of the small amount of the quinonoid structures and/or the overlap of the spectra of these species l6 On the other hand, it is difficult for the dinitrene created from DAF to form a twisted biphenyl skeleton, because the two phenyl nngs of DAF are connected by a methylene Thus the difference in the absorption spectrum between dinitrenes photogenerated from DAF and DADMB can be mainly ascribed to the presence or absence of a twisted biphenyl skeleton Photodecomposition of DAF in cyclohexane solution at room temperature As mentioned above, we found that DADMB is a quite unusual aromatic azide compound the photolysis of DADMB never gives didehydroazepine derivatives in inert cyclohexane solu- tion" The above result was obtained on the basis of the following experimental observations although didehydroazep- me denvatives are known to react with diethylamine (DEA), no effect was observed on the addition of DEA to a DADMB- cyclohexane solution either for the transient absorption spectra or for the time profiles of the transient absorption of the solution An isosbestic point was clearly observed for the temporal evolution of the absorption spectra induced by photolysis Both the decay of the triplet azido nitrene of the intermediate and the formation of the final product obeyed second-order kinetics, which indicates that the final product is the azo compound (N,-R -N=N-R -N3) produced via dimerization of two triplet azido nitrenes Fig 2 shows the transient absorption spectra of a DAF-cyclohexane solution in the absence of DEA The transient absorption with a peak around 380nm at 0-20ns decreases with increasing delay time and changes to an absorption with a peak at ca 350nm The latter absorption spectrum at 100-160 ns agrees with the transient absorption spectrum at 2 ps These spectra are similar to those observed after one or three laser shots for the DAF-rigid glass at 77 K (Fig l), indicating that the absorption spectrum with a peak at 350 nm is due to the triplet azido nitrene The initial decay of the transient absorption at 380 nm was completed within the duration of the laser pulse This result indicates that the formation of the triplet azido nitrene in cyclohexane solution is completed within the duration of the laser pulse No evolution of the absorption spectra was observed in the time region on and after 10 ms, indicating that the reaction was finished within 10 ms and that the absorption spectrum at 10 ms is due to final products of DAF after the photolysis in cyclohexane solution Although an isosbestic point is observed in the time region from 20 to 200ps, the isosbestic point is not observed over the reaction time region from 2 ps to 10 ms, suggesting that three or more species contribute to the absorption spectra This result is quite different from that for the DADMB-cyclohexane solution system Since the triplet azido nitrene is the main component in the solution at 2 ps after laser excitation, the absorption spectral change shown in Fig 2 is mainly ascribed to dimerization of two triplet azido nitrenes created from DAF, which produces the azo compound (N, -R-N=N-R-N,), 2,2 -diazido-7,7 -azofluorene The wavelengthhm Fig.2 Transient absorption spectra of 3.3 x lo-' mol dm-3 DAF- cyclohexane solution. Laser fluence: 4.9 mJ cm-2. Time region: (A)ns and (B)ps and ms. (A)Gate times: (a)0-20 ns; (b)100-160 ns. (B)Delay times: (a)2, (b)20, (c) 60, (d) 100, (e)200 ps, (f)1 and (g) 10 ms. formation of azo compounds by the dimerization of triplet nitrenes created from aromatic azides is well kn~wn.',~~-l~ NEt, 3 4 As previously mentioned, three or more species contribute to the transient absorption spectra.The photodecomposition mechanism of normal aromatic azide compounds suggests that photolysis of DAF generates didehydroazepine derivatives (3) in addition to the azido nitrene. To confirm the presence of the didehydroazepine derivatives, we examined the effect of DEA addition to the DAF-cyclohexane solution. As shown in Fig. 3, the transient absorption spectra of the DAF-cyclohex- ane solution in the presence of DEA are different from those in the absence of DEA, while changes in the absorption spectra were completed within 10 ms.A shoulder around 380 nm and a descending tail at longer wavelength in the absorption spectrum at 2 ps are clearly observed, and they seem to be observed also for the spectrum at 10 ms. The latter observation indicates that they are due to one of the final products after the photolysis of the DAF-cyclohexane solution in the presence of DEA. These results combined with the results reported for normal aromatic azide compounds suggest that the shoulder and the descending tail in the spectrum at 2 ps can be assigned to the reaction product, 3H-azepine derivative (4), of DEA with didehydroazepine derivative (3)created from DAF. Hence the photolysis of a DAF-cyclohexane solution gives both the triplet azido nitrene and the azido didehydroazepine derivative, which is a quite different result from that obtained with the DADMB system.Of course, as previously mentioned, the triplet azido nitrene is seen to be predominant because of the clear observation of the absorption bands around 350, 525 and 572nm assigned to the triplet azido nitrene even in the spectra in the presence of DEA (the latter two bands are not shown in Fig. 3). Hence, reactions related to didehydroazepines (3) such as the reaction of 3 with DAF seem to contribute to the spectral change observed for laser irradiation of a DAF- ,0.2 0.1 O~"l''l'''l''ll'J400 500 wavelengthhm Fig. 3 Transient absorption spectra of 3.3 x mol dmP3 DAF- cyclohexane solution in the presence of 0.15 mol dm-3 diethylamine (DEA).Delay times: (a) 2, (b)20, (c) 60, (d) 100, (e) 200 ps, (f)1 and (g) 10 ms. dimerizationN,-R-N, 3~N-R-N, k ( < 10 ms) N, -R-N =N-R-N, (main process) -N2 v 3 --+HNEt, 4 (minor process) Scheme 1 Photoreaction of DAF in cyclohexane cyclohexane solution in the absence of DEA (Fig. 2), in addition to the dimerization reaction of triplet azido nitrenes to the corresponding azo compound. The present experimental results suggest that the photoreac- tion mechanism of DAF in inert cyclohexane solution is as shown in Scheme 1, where the formation of both azido nitrene and 3 is finished within the duration of the laser pulse. Photodecomposition of DAF in PMMA films Irradiation of diazide compounds with a single laser shot of low fluence gives predominantly the triplet azido nitrene. Results for IR and GPC measurements of the final photoprod- ucts of normal aide compounds showed that reaction of nitrenes (Ar-N) in polymer matrices (P-H) generates aryl- amino radicals (Ar -NH) and polymer radicals (P') as prob- able intermediates, and primary amines (Ar -NH,), polymeric secondary amines (Ar- NH-P), and crosslinked polymers (P-P) as final product^.'^ In the case of DADMB-doped PMMA films, the absorption spectrum of the triplet azido nitrene was similar to that of the primary amine, while the absorption spectrum of the arylamino radical, which is one of the probable intermediates, was not identified because of the similarity in absorption spectra among these three species." The transient absorption spectra of 1% w/w DAF-doped PMMA films induced by laser irradiation with a low fluence of 5.2 mJ cm-' are shown in Fig.4. The absorption spectrum at 1 ps is similar to that observed upon one or three shots in a DAF-rigid glass at 77 K (Fig. 1)and that at 2 ps in a DAF- cyclohexane solution [Fig. 2(B)]. This indicates that the absorption spectrum at 1 ps is mainly due to the triplet azido nitrene (2-azido-7-nitrenofluorene). The changes in the transi- ent absorption spectra were complete within 100 s (Fig. 5). J. Muter. Chem., 1996, 6(5), 705-710 707 0.4-wavelengthhm Fig. 4 Transient absorption spectra of 1Yo w/w DAF-doped PMMA films Laser fluence 5 2 mJ cm Delay times (a) 1 p, (b) 1, (c) 5, (d) 10, (e) 100, (f)500 ms, (g) 1, (h)5, (I) 10, (1)30, (k) 60 and (1) 120s 0 0 0 0 0 0 0 .a.I 0-5 1oo t Is Fig. 5 Time dependence of the transient absorbance monitored at 350 (closed symbols) and 500 nm (open symbols) (@, 0)1 % w/w and (U, 0)10% w/w DAF-doped PMMA films Laser fluence was 5 2 mJ cm for both the films The value at 0 ps was plotted at 10 s (1 ps) This reaction time is short compared with that observed for DADMB-doped PMMA films irradiated by a laser (>1200~)~~The long reaction time compared with that in cyclohexane solution (<lo ms) and the difference in the absorption spectrum of the final product between films and solution indicates that the dimerization of the azido nitrene does not occur in PMMA films and that the triplet azido nitrene reacts with the polymer, as expected We notice that the absorbance at 350nm increases with increasing delay time from 2 ps to 1 ms and then decreases up to several tens of seconds (Fig 5) The latter behaviour is considered to be due to the formation of final products related to the reaction of azido nitrenes with PMMA The absorption spectrum of the final products was quite similar to that of a 1% w/w DADMB-doped PMMA film irradiated with a low 708 J Mater Chem, 1996, 6(5), 705-710 fluence" The latter absorption spectrum was assigned to a primary amine (4-amino-4'-azido-3,3'-dimethoxybiphenyl N3-R-NH2) created from the reaction of PMMA with the azido nitrene (4-azido-3,3'-dimethoxy-4-nitrenobiphenyl N, -R'-N) formed by photodecomposition of DADMB These results suggest that the absorption spectrum of the final products in the present system is mainly due to primary amine (2-amino-7-azidofluorene N3-R-NH2) Fig 6 shows the transient absorption spectra of 10% w/w DAF-doped PMMA films induced by laser irradiation with a low fluence of 5 2 mJ cm-' The absorption spectrum at 0 ps was also similar to that of the triplet azido nitrene, indicating the formation of the triplet azido nitrene in the film The changes in the absorption spectra were also complete within 100 s (Fig 5), and the absorption spectrum of final products was similar to that of dilute samples (Fig 4) The latter suggests that the final product is mainly primary amine For the present concentrated sample, the change in the absorbance at 350 nm with increasing delay time is similar to that for a dilute one an increase with increasing delay time from 0 ps to 1 ms and a decrease up to several tens of seconds The former increase in the absorbance at 350 nm observed for both the samples is not considered to be due to the conversion from azido didehy- droazepine to the triplet azido nitrene, since the lifetime of the azido didehydroazepine is short and its concentration is low Hence the increase is ascribed to an increase in the concen- tration of the intermediate (arylamino radical, N, -R-NH) created by hydrogen abstraction from PMMA by nitrene groups This suggests that the absorption spectrum of the arylamino radical is similar to those of the triplet azido nitrene and the primary amine (one of the final products, as previously mentioned), which is quite similar to the results on DADMB Fig 7 shows the absorption spectra at 0, 1 or 2 ps (A)and the absorption spectra of final products (B)observed for DAF- doped PMMA films irradiated with various excitation laser fluences In the case of DADMB-doped films, the absorption due to the dinitrene was observed for spectra at 0 ps of sample films irradiated with a high fluence lo As for DAF-doped films, although the absorption spectrum with a vibrational structure ascribable to the dinitrene (Fig 1)is not clearly observed for sample films irradiated with a high fluence, the presence of both the absorption peak around 390nm and the shoulder 0 Y Q,0C (d-s nz 400 500 600 400 500 600 wavelengthhm Fig.6 Transient absorption spectra of 10% w/w DAF-doped PMMA films Laser fluence 5 2 mJ cm Delay times (a) 10, (b) 100 ps, (c) 1, (d) 10, (e)100, (f)500 ms, (g)1, (h)5, (1) 60 and (1) 120s 400 500 600 400 500 600 wavelengthhm Fig. 7 Dependence of irradiation laser fluence on (A)transient absorp- tion spectra observed at (a)-(c) 1, (d) 0, (e) 2 and (f) 1 ps and (B) absorption spectra of the final products. Laser fluence: (a) 5.2, (b) 8.7, (c) 26.7, (d) 5.2, (e) 9.0 and (f) 20.8 mJ cm-2. Samples: (a)-(c) 1% w/w and (d)-(f) 10% w/w DAF-doped PMMA films. around 410 nm observed for 1% w/w DAF sample films suggests the presence of the dinitrene photogenerated from DAF.The absorption spectra of the final products around 420 nm observed for both 1 and 10% w/w samples irradiated with a low fluence are almost the same [Fig. 7(B)(a) and (41. Even for dilute samples ( 1% w/w), however, the broad absorption of the final product around 420 nm increases with laser fluence, which is quite different from what was observed for 1% w/w DADMB-doped films, where the absorption spectra were almost independent of the laser fluence and were similar to that observed with 10% w/w samples irradiated with a low fluence." These results suggest that DAF molecules form aggregates even in dilute (1% w/w) PMMA films and, as a consequence, under irradiation with a high fluence, dimeriz- ation and/or polymerization of triplet azido nitrenes and/or dinitrenes takes place in the aggregates. The presence of such reactions is supported by the fact that the absorption spectrum of the final products induced by laser irradiation with a high fluence of 26.7 mJ cm-2 for 1% w/w DAF samples is quite similar to that with a high fluence of 31.8 mJ cm-2 for 10% w/w DADMB samples reported previously.1° The latter spec- trum was assigned to the photoreaction products produced via dimerization and/or polymerization of triplet azido nitrenes and/or dinitrenes." When 10% w/w DAF-doped PMMA films were irradiated with a laser with a high fluence of 20.8 mJ cm-2, the transient absorption spectra changed drastically during 10 ps after laser irradiation, and no change was observed after 10 ps.This rapid change in the spectra is ascribed to rapid dimerization and/or polymerization of a large number of azido nitrenes and/or dinitrenes, produced by laser irradiation with a high fluence, in large DAF-aggregates in PMMA films. The present experimental results suggest the photoreaction mechanism for DAF in PMMA films shown in Scheme 2. The absorption spectrum of the triplet azido nitrene (N, -R-N) is similar to that of the final product, primary amine (N, -R-NH2), and furthermore the absorption spectrum of the amino radical (N,-R-NH) of the most probable inter- (irradiation with a high fluence) -2N2 (within the duration of the laser pulse) :N-R-N: N3-R-N: reaction /,' dimerization reaction withwith and/orpolymers ; polymerization polymers (<loos)(cloos) ; (c10ps for 10% w/w I I t, \sample) intermediat8: I N,--R-NHII t \ final products e.g.final products(:N-R-N=N-R-N=N-R-N:) ( main product: polymeric products N,-R-NH,) Scheme 2 Photoreaction of DAF in PMMA films mediate was also suggested to be similar to them. Hence we were not able to resolve the time-resolved absorption spectra into each component of these species and, as a consequence, we cannot discuss dynamics of the photochemical reaction of DAF in PMMA matrix in detail. When laser fluences are large, different photoreaction behav- iour was observed for DADMB- and DAF-doped PMMA films. DADMB does not form aggregates in 1% w/w-doped PMMA films," while DAF is suggested to form aggregates even in the same dopant concentration.This is due to the difference in miscibility of these diazide compounds in PMMA because of the presence or absence of methoxy groups. The different chemical structure and the different miscibility result in the difference in location of diazide compounds in PMMA films, inducing a difference in the reactivity of azido nitrenes with PMMA. Thus the large difference in the photoinduced reaction time between DAF (<100 s) and DADMB (>1200 s) in PMMA films is also considered to be due to the different miscibility. The present results combined with those of DADMB indicate the importance of the miscibility of azide compounds in polymer matrices.The distribution of sensitizers in negative photoresist films is important in assuring retention of the exposed regions and uniform dissolution of the unexposed regions. Aggregation of sensitizers may cause the creation of pits in the film surface and result in images with uneven edges. Hence information on the miscibility of azide compounds in polymer matrices is important for photolithographic applications. By applying a laser flash photolysis method to sensitizer-doped polymer films, one can obtain such information. References 1 T. Yamaoka, H. Kashiwagi and S. Nagakura, Bull. Chem. SOC.Jpn., 1972,45,361. 2 M. Sumitani, S. Nagakura and K. Yoshihara, Bull. Chem. SOC.Jpn., 1976,49,2995. 3 A. K. Schrock and G.B. Schuster, J. Am. Chem. SOC.,1984, 106, 5228. 4 A. K. Schrock and G. B. Schuster, J. Am. Chem. SOC.,1984, 106, 5234. 5 T. Kobayashi, H. Ohtani, K. Suzuki and T. Yamaoka, J. Phys. Chem., 1985,89,776. 6 E. Leyva, M. S. Platz, G. Persy and J. Wirz, J. Am. Chem. SOC., 1986,108,3783. 7 C. J. Shields, D. R. Chrisope, G. B. Schuster, A. J. Dixon, M. Poliakoff and J. J. Turner, J. Am. Chem. SOC.,1987,109,4723. J. Muter. Chern., 1996,6( 5), 705-710 709 8 9 10 T -YLiang and G B Schuster, J Am Chem SOC ,1987,109,7803 A Miura and T Kobayashi, J Photochem Photobiol A Chem, 1990,53,223 A Itaya, T Inoue, T Yamamoto, T Nobutou, H Miyasaka, M Tonumi and T Ueno, J Mater Chem ,1994,4,1539 14 15 16 A Marcinek, E Leyva, D Whitt and M S Platz, J Am Chem SOC,1993,115,8609 A Reiser, H M Wagner, R Marley and G Bowes, Trans Faraday SOC,1967,63,2403 T Ohana, M Kaise, S Nimura, 0 Kikuchi and A Yabe, Chem 11 M Tonumi, N Hayashi, M Hashunoto, S Nonogaki, T Ueno and T Iwayanagi, Polym Eng Scz ,1989,29,868 17 Lett, 1993,765 S Nonogaki, Polymer J,1987,19,99 12 K T Hatton, T Hatton, S Uchino, T Ueno, N Hayashi, S Shirai, N Monuchi and M Monta, Jpn J Appl Phys, 1992, 31,4307 Paper 5/05830I, Received 4th September 1995 13 T-Z Li, J P Kirby, M W George, M Poliakoff and G B Schuster, J Am Chem SOC, 1988,110,8092 710 J Mater Chem, 1996,6(5), 705-710

ISSN:0959-9428    

DOI:10.1039/JM9960600705

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Novel optically transparent polyesters containing a high density of second-order non-linear optically active chromophores Nobukatsu Nemoto," Fusae Miyata," Yu Nagase,"* Jiro Abe,b Makoto Hasegawab and Yasuo Shiraib "Sagami Chemical Research Center, 4-4-1 Nishi-Ohnuma, Sagamihara, Kanagawa 229, Japan bDepartment of Photo-optical Engineering, Faculty of Engineering, Tokyo Institute of Polytechnics, 1583 Iiyama, Atsugi, Kanagawa 243-02, Japan The syntheses and second-order non-linear optical (NLO) properties of novel types of optically transparent polyesters containing a high density of second-order NLO-active chromophores are described. The chromophores used in this study contained either a perfluorooctyl- or an octyl-sulfonyl moiety as the electron-withdrawing group at the n-conjugating sites.The polyesters are prepared by condensation polymerization between isophthalic acid derivatives and 2-[N-( 2-hydroxyethyl)-4- (perfluorooctylsulfony1)anilino]ethanol by the use of triphenylphosphine and diethyl azodicarboxylate as the condensation reagents. The amorphous polyesters obtained, the optical transparency of which was down to 390 nm, exhibited good solubility in common organic solvents and provided optical-quality films by spin-coating. In addition, second-harmonic generation (SHG) measurements of spin-coated films of the polyesters were carried out by the Maker fringe method using a Q-switched Nd : YAG laser as the exciting beam after poling treatment. One of the polyesters, which was prepared from 5-{2-[N-methyl-4- ( perfluorooctylsulfonyl)anilino] ethoxy) isophthalic acid and 2-[N-( 2-hydroxyethyl)-4-( perfluorooctylsulfony1)anilino] ethanol, exhibited the desired optical-transparency and a second-order NLO coefficient, d33, of 3.0 pm V-l.In recent years, polymeric materials with second-order non- linear optical (NLO) properties have been required for NLO applications such as fast waveguide and electro-optic modu- lation. In many cases, polymeric materials incorporating aro- matic molecules that contain both electron-donating and electron-withdrawing groups at the n-conjugate sites have been the subject of intense studies.1-8 However, one difficulty with polymeric second-order NLO materials is that most of these chromophores tend to align in a centrosymmetric space group.Thus, second-order NLO susceptibility, x(~),vanishes in spite of high microscopic optical non-linearity, p. Therefore, high qpolymers such as aromatic polyimide~,~-'~ aromatic poly- amides,14-16 aromatic polyurethane^'^-^^ and aromatic poly- ester~"-~~have been used as polymeric matrices for the purpose of restraining the relaxation of the noncentrosymmetric chromophore-alignment induced by an electric field. However, organic molecules which contain both electron- donating and electron-withdrawing groups at n-conjugate sites have large /3 values since a high degree of delocalization gives a large value of p.35936 As a result, an intramolecular charge- transfer absorption is caused in visible region.In contrast, second-order NLO materials with short cutoff wavelengths are desirable for practical use because the absorption of the second harmonic wave generated by the near-infrared wave of diode lasers causes intolerable damage to materials. Therefore, there should be a trade-off between optical non-linearity and the cutoff wavelength. Indeed, some effort has been made to produce second-order NLO materials with blue shifted cutoff In general, aromatic-containing polyester matrices, which are easily prepared from the corresponding dicarboxylic- and dihydroxy-functionalized monomers, exhibit relatively high q and optical transparency. In fact, the preparation of second-same functionality, i.e. second-order NLO active chromophore moieties, a high chromophore concentration in the polymer matrices should result.We have proposed that a high chromo- phore concentration in polymer matrices should result in a high second-order NLO s~sceptibility.~~ From these perspectives, we report here the syntheses of novel types of polyesters obtained by the condensation poly- merization of two comonomers, both of which contain second- order NLO active chromophore moieties as shown in Scheme 1. The chromophore used in this study contained a perfluorooctyl- or octyl-sulfonyl moiety as the electron-with- drawing group to achieve optical transparency down to 400nm. In addition, the thermal, linear optical and second- order NLO properties of the polyesters obtained are also reported. Experimenta1 Materials N,N-Dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were distilled over CaH, under reduced pressure, and tetrahydrofuran (THF) was distilled twice (over CaH, and sodium) to remove traces of water.Diethanolamine, N-methyl- ethanolamine, 4-hydroxypiperidine, 4-(2-hydroxyethyl)piper-idine, diethyl azodicarboxylate (Tokyo Kasei Kogyo Co.), 4-fluorothiophenol (4-fluorobenzenethiol) (Aldrich Chemical Company), acetic acid, 30% aqueous hydrogen peroxide ( Wako Pure Chemical Industry) and perfluorooctyl iodide were commercially available and used as received. 1-Bromooctane was purchased from Tokyo Kasei Kogyo Co. and purified by distillation under reduced pressure. Triphenylphosphine was purchased from Tokyo Kasei Kogyo Co., and purified by recrystallization from ethanol prior to order NLO active main-~hain-~~"~ use.Dimethyl 5-hydroxyisophthalate was prepared by methyl and side-~hain-type~~q~~ polyesters have been reported as mentioned above. Our pri- esterification of 5-hydroxyisophthalic acid with methanol mary interest was to investigate the NLO properties of poly- catalysed by sulfuric acid as reported elsewhere.45 esters which can be easily processed owing to the alternate alignment of the same or different functionalities. This can be Instrumentation easily realized by using comonomers with the same or different UV-VIS absorption spectra were recorded on a Hitachi Model functionalities. For example, if each comonomer contains the U-3200 spectrophotometer.'H NMR and 19F NMR were J. Muter. Chem., 1996, 6(5),711-717 711 (F-phenyl-S-CF,+), 169 [CF,(CF,),+], 127 (F-phen-OQ" H4 yl-S+), 119 (CF3CFz+),95 (F-phenyl'), 69 (CF,+) Od HdbH jl r 1 L Pl-P4 Scheme 1 Reagents and conditions 1, PPh,, diethyl azodicarboxylate (DEAD), dimethyl sulfoxide (DMSO), 100"C, 12 h recorded on a Hitachi R-90H FT NMR (90 MHz) spectrometer and a Bruker AC200P FT NMR (200MHz) spectrometer, respectively J values are given in Hz DSC measurements were carried out on a Shimadzu Model DSC-50 under a helium flow rate of 20 ml min-l and a heating rate of 10"C min-' Gel permeation chromatography (GPC) was performed on a Tosoh HLC-802A instrument equipped with TSK gels G5000H6, G4000H6, G3000H6, and G2000H6 using poly- styrene standards with THF as eluent X-Ray diffraction patterns were recorded on a MAC Science MXP3 X-ray diffractometer, equipped with a thermal controller Model 53 10 4-Fluorophenyl perfluorooctyl sulfide (1) Sulfide 1 was prepared using a modification of the method of Feinng et al 46 47 Under an argon atmosphere, 4-fluorothio- phenol (10 40 g, 81 1mmol) in dry DMF (10 ml) was added dropwise to sodium hydride (60% in mineral oil, 3 75 g, 93 8 mmol) suspended in dry DMF (40 ml) in an ice bath The reaction mixture was stirred at ambient temperature for 1 h, and then perfluorooctyl iodide (35 42 g, 64 9 mmol) was added dropwise After the reaction mixture had been stirred at ambient temperature for 16 h, the DMF was evaporated under reduced pressure Water and diethyl ether were added to the residue, and the organic layer was washed with water The organic layer was dried over anhydrous sodium sulfate and the solvent was evaporated The crude product was purified by silica gel column chromatography with hexane as eluent to give the title compound 1 as a colourless liquid (30 6 g, 86%), GH(CDCl,, 90 MHz) 7 0-7 2 (m, 2 H, Ar-H), 7 5-7 7 (m, 2 H, Ar-H), G,(CDCl,, CFC1,) -126 6 (m, 2 F), -123 2 (m, 2 F), -122 3 (m, 4F), -121 7 (m, 2 F), -119 6 (m, 2 F), -108 7 (m, 1 F, F-Ph), -87 7 (m, 2 F, -CFz-S-), -81 3 (t, J 9 9, 3 F, -CF,), vmax/cm-' 2920, 2850, 2905, 2825, 1590, 1490, 1400, 1365, 1320, 1240 (perfluoroalkyl), 1210 (perfluoroalkyl), 1145, 1115, 1100, 1020, 945, 935, 835, 780, 760, 720, 700, 670, 655, 560, 520, m/z 546 (M'), 527 (M+-F), 177 712 J Mater Chem, 1996, 6(5),711-717 4-Fluorophenyl octyl sulfide (2) Sulfide 2 was prepared by a similar method as for the prep- aration of 1 using 1-bromooctane as a raw material Purification by silica gel column chromatography with hexane as eluent gave the title compound 2 as a colourless liquid (85%), d,(CDCl,, 90MHz) 07-1 9 [m, 15H, CH3(CHz),CHz-], 2 85 (t, J 6 9, 2 H, -CHZ-S-), 6 8-7 2 (m, 2 H, Ar-H), 7 2-7 5 (m, 2 H, Ar-H), v,,,/cm-' 2960,2930, 2950,1590,1490,1460,1380,1260,1230, 1160, 1090,1010,820, 720,630,500, m/z 240 (M'), 141 (F-phenyl-S-CH,'), 127 (F-phenyl-S'), 71 (C5Hllf), 57 (C4H,+), 43 (C,H,+), 29 (C2H5+) 4-Fluorophenyl perfluorooctyl sulfone (3) A mixture of 1 (16 39 g, 30 0 mmol), acetic acid (60 ml) and hydrogen peroxide (30% aqueous, 17 01 g, 150mmol) was refluxed for 12h The reaction mixture was poured into saturated aqueous sodium hydrogen carbonate (300 ml) The crude product was extracted with chloroform (50 ml x 6), and the combined chloroform extracts were dned over anhydrous sodium sulfate The chloroform was evaporated and the residue was purified by silica gel column chromatography with hexane as eluent Finally, recrystallization of the product from hexane provided the title compound 3 (15 1 g, 87%), d~(cDC13, 90MHz) 72-76 (m, 2H, Ar-H), 80-84 (m, 2H, Ar-H), dF(CDC1,, CFC1,) -126 6 (m, 2 F), -123 2 (m, 2 F), -122 2 (m, 6F), -1202 (m, 2F), -1117 (m, 2F), -979 (m, lF, F-Ph), -81 2 (t, J 9 8, 3 F, -CF,), vmax/cm-' 3110, 3070, 2905,1590,1495,1410,1370, 1330,1305,1250 (perfluoroalkyl), 1205 (perfluoroalkyl),1150 (-SOz-), 1080, 1055, 1015, 850, 820, 745, 710, 690, 655, 605, 580, 550, 540, 515, 495, m/z 559 (M+ -F), 169 [CF,(CF,),+], 159 (F-phenyl-SO,'), 119 (CF3CFz+),95 (F-phenyl+), 69 (CF,') 4-Fluorophenyl octyl sulfone (4) Sulfone 4 was prepared by a similar method as for the preparation of 3 using 2 as the raw material Purification by silica gel column chromatography with hexane as eluent gave the title compound 4 as colourless crystals (82%), dH(CDC1,, 90 MHz) 07-1 9 [m, 15 H, CH3(CHz)6CH2-], 3 0-3 3 (m, 2 H, -CH,-SO2-), 7 1-7 5 (m, 2 H, Ar-H), 7 8-8 2 (m, 2 H, Ar-H), v,a,/cm-l 2960, 2920, 2950, 1600, 1500, 1470, 1410, 1320, 1280, 1240, 1150 (-SOz-), 1090, 1010, 840, 820, 770, 730, 680, 570, 530, 450, m/z 272 (M'), 187 (F-phenyl-SOz-C2H4+), 173 (F-phenyl-SO, -CHzf), 159 (F-phenyl-SO,'), 95 (F-phenyl'), 71 (C5Hll+),57 (C4H9+ ), 43 (C3H7+ 1, 29 (CZH5+ 2-[N-Methyl-4-( perfluorooctylsulfonyl )anilino] ethanol (5) Under an argon atmosphere, dry DMSO (3 ml) was added to a mixture of N-methylethanolamine (0520 g, 6 92 mmol) and anhydrous potassium carbonate (1 06 g, 7 70 mmol) To this mixture, 3 (4 00 g, 6 92 mmol) was added The reaction mixture was stirred at 100°C for 12 h and then poured into water (300 ml) The resulting precipitate was collected by filtration and recrystallized from methanol to give the title compound 5 (3 92 g, 90%), GH(CDC1,, 90 MHz) 1 65 (t, J 5 1, 1 H, -OH), 3 16 (s, 3H, -N-CH3), 364 (t, J 51, 2H, -N-CHz-), 3 87 (t, J 5 1, 2H, -0-CH2-), 681 (d, J 92, 2 H, Ar-H), 7 77 (d, J 9 2, 2 H, Ar-H), vmax/cm-' 3580 (-OH), 1240 and 1210 (perfluoroalkyl), 1160 (-SOz-), m/z 633 (M'), 214 CM+ -(C*F17)I7 169 CCF,(CFz)z+l, 150 CM+ -(S02C8F,,)I, 119 [CF3CFz+ or Ph-N(CH3)CHzf], 69 (CF,') (Found C, 32 2, H, 165, N, 2 0 Calc for CI7Hl2NO3Fl7S C, 3224, H, 191, N, 2 21%) 1-[ 4-( Pe~uorooctylsulfony1 )phenyl] piperidin-4-01 (6) and 2-{1-[ 4-( perfluorooctylsulfonyl)phenyl] piperidin-4-yl )ethanol (7) Piperidines 6 and 7 were prepared by a similar method as for the preparation of 5 using 4-hydroxypiperidine and 4-( 2- hydroxyethy1)piperidine instead of N-methylethanolamine as the raw materials, respectively.Compound 6 (90%); 6,(CDCl,; 90 MHz) 1.5-2.2 (m, 5 H, 4 x piperidinyl-H and -OH), 3.2-4.2 (m, 5 H, piperidinyl-H), 6.93 (d, J 9.2, 2 H, Ar-H), 7.76 (d, J 9.2, 2 H, Ar-H); vmax/cm-l 3250 (-OH), 1240 and 1210 (perfluoroalkyl), 1160 (-SO2-); WZ/Z659 (M'), 240 [M' -(c8F17)], 176 [M+ -(SO2c,F17)], 169 [CF,(CF,),+], 119 (CF3CF2+), 69 (CF,+). (Found: C, 34.5; H, 2.0; N, 2.0. Calc. for Cl9Hl4NO3Fl7S: C, 34.61; H, 2.14; N, 2.12%). Compound 7 (87%); dH(CDC1,; 90MHz) 1.2-1.7 (m, 4H, 3 x piperidinyl-H and -OH), 1.7-2.1 (m, 4 H, piperidinyl-H), 3.00 (t, J 12.5, 2 H, -CCH2-piperidine), 3.6-4.2 (m, 4H, 2 x piperidinyl-H and -CCH2-OH), 6.90 (d, J 9.2, 2 H, Ar- H), 7.76 (d, J 9.2, 2 H, Ar-H); vmax/cm-l 3360 (-OH), 1250 and 1210 (perfluoroalkyl), 1150 (-SO2-); m/z 687 (M+), 268 CM+ -(c8F17)1, 204 cM+ -(S02C8F17)1, 169 CCF,(CF2)2+I, 119 (CF3CF2+), 69 (CF,'). (Found: C, 36.6; H, 2.55; N, 2.0.Calc. for C21H18NO3F17S: C, 36.69; H, 2.64; N, 2.04%). 2-[N-Methyl-4-(octylsulfonyl)aniline]ethanol (8) Aniline 8 (90%) was prepared by a similar method as for the preparation of 5, using 4 instead of 3 as the raw material; ~H(CDCI,;90 MHZ) 0.7-1.9 [m, 16 H, CH,(CH2)&H2- and -OH], 2.9-3.2 (m, 2 H, -CH2-SO2-, overlapped by a singlet signal at 6 3.09), 3.09 (s, 3 H, -N-CH,), 3.58 (t, J 5.1, 2 H, -N-CH2-), 3.82 (t, J 5.1, 2 H, -CCH2-OH), 6.76 (d, J 9.0, 2 H, Ar-H), 7.66 (d, J 9.0, 2 H, Ar-H); vmax/cm-l 3250 (-OH), 1160 (-SO2-); rn/z 327 (M+), 214 [Mf-(C8H17)1, l50 [M+ -(SO2C8H17)], 71 (C5H11'), 57 (C4H9'), 43 (C3H7+), 29 (C2H5').(Found: C, 62.1; H, 9.1; N, 4.25; S, 9.8. Calc. for C17H29N03S: C, 62.35; H, 8.93; N, 4.28; s, 9.79%). Dimethyl 5-substituted isophthalate derivatives (9-12) Typical procedures, applying the Mitsunobu reaction,48 are as follows. Under an argon atmosphere; 5 (1.267 g, 2.0 mmol), dimethyl 5-hydroxyisophthalate (0.631 g, 3.0 mmol), and tri- phenylphosphine (0.63 1 g, 2.4 mmol) were dissolved in dry THF (10 ml) in an ice bath. To this solution diethyl azodicar- boxylate (0.51 g, 3.0 mmol) was added dropwise, and the mixture was stirred at ambient temperature for 1 h. The solvent was evaporated and the residue was purified by silica gel column chromatography with chloroform as eluent.Finally, recr ys t alliza tion from ace t one-me thanol provided dime t h yl 5-{ 2-[N-methyl-4-( perfhorooctylsulfony1)anilino] ethoxy} iso- phthalate (9) (1.53 g, 93%), mp, 135 "C (determined from the DSC thermogram); G,(CDCl,; 90MHz) 3.22 (s, 3 H, -N-CH,), 3.8-4.1 (m, 2 H, -N-CH2-, overlapped by a singlet signal at 6 3.93), 3.93 (s, 6 H, -COOCH,), 4.28 (t, 2H, J 5.1, -0-CH2-), 6.83 (d, J 9.2, 2H, anilino-H), 7.71 (d, J 1.1, 2 H, isophthalate Ar-H), 7.82 (d, J 9.2, 2 H, anilino- H), 8.29 (s, 1 H, isophthalate Ar-H); vmaX/cm-' 1720 (-C=O), 1250 and 1230 (perfluoroalkyl), 1120 (-SO2-); m/z 825 +(M ), 61 6 [+CH2CH2N(CH3)-phenyl- S02C8F17], 406 [M' -(C*F17)], 342 [M+ -(SO2C,F17)], 179, 169 [CF,(CF,),+], 119 (CF3CF2+), 69 (CF,').(Found: C, 39.3; H, 2.3; N, 1.5. Calc. for C27H20N07F17S: C, 39.28; H, 2.44; N, 1.70%); Amax(CHC13)/nm (~/1 mol-I cm-l), 309 (42 660; Ll,off/nm, 348. Isophthalates 10-12 were prepared by the similar method as for the preparation of 9 using 6-8 as the raw materials instead of 5, respectively. Compound 10 (72%), mp 128 "C (determined from the DSC thermogram); d,(CDC13; 90 MHz) 1.9-2.3 (m, 4 H, piperidinyl- H), 3.5-3.9 (m, 4 H, piperidinyl-H), 3.95 (s, 6 H, -COOCH,), 4.7-5.0 (m, 1 H, piperidinyl-H), 6.96 (d, J 9.2, 2 H, anilino-H), 7.71 (d, J 1.1, 2 H, isophthalate Ar-H), 7.82 (d, J 9.2, 2 H, anilino-H), 8.30 (s, 1 H, isophthalate Ar-H); vmax/crn-l 1730 (-C=O), 1250 and 1210 (perfluoroalkyl), 1160 (-SO2-); rn/z 851 (M'), 642 {M' -[OPh(COOCH,),]), 432 [M+ -(CsF17)], 368 [M' -(S02CgF17)], 179, 169 [CF,(CF,),+], 119 (CF3CF2+), 69 (CF,+).(Found: C, 41.0; H, 2.5; N, 1.4. Calc. for C2,H22N07F17S: C, 40.91; H, 2.60; N, 1.64%). RmaX(CHC1,)/nm (~/1 mol-l cm-l), 312 (43 060); &,toff/nm, 350. Compound 11 (64%), mp 117 "C (determined from the DSC thermogram); d,(CDCl,; 90 MHz) 1.2-1.7 (m, 3 H, piperidinyl- H), 1.7-2.2 (m, 4H, piperidinyl-H), 3.12 (t, J 11.6, 2H, -CCH,-piperidine), 3.94 (s, 6 H, -COOCH3), 4.0-4.3 (m, 4 H, 2 x piperidinyl-H and -CH2 -0-), 6.91 (d, J 9.2, 2 H, anilino-H), 7.71 (d, J 1.1, 2 H, isophthalate Ar-H), 7.82 (d, J 9.2,2 H, anilino-H), 8.29 (s, 1 H, isophthalate Ar-H); vmax/cm-l 1730 (-C=O), 1240 and 1210 (perfluoroalkyl), 1160 (-SO2-); WZ/Z 879 (M'), 670 {[M+ -[OPh(COOCH,)2]}, 460 [Mf-(C8F,7)], 396 [M+-(SO2C8F17)], 179, 169 [CF,(CF,),+], 119 (CF3CF2'), 69 (CF,+).(Found: C, 42.3; H, 2.7; N, 1.3. Calc. for C31H26N07F17S: C, 42.33; H, 2.98; N, 1.59%); ~max(CHCl,)/nm (~/1 mol-l cm-l), 316 (48 780); Lltoff/nm, 351. Compound 12 (6l%), mp 92 "C (determined from the DSC thermogram); GH(CDC1,; 90 MHz) 0.7-1.9 [m, 15 H, CH3(CH2)6CH2-], 2.9-3.2 (m, 2 H, -CH2-SO2-, over-lapped by a singlet signal at 6 3.16), 3.16 (s, 3 H, -N-CH,), 3.8-4.0 (m, 2 H, -N-CH2-, overlapped by a singlet signal at 6 3.93), 3.93 (s, 6 H, -COOCH,), 4.25 (t, J 4.8, 2 H, -CH,-0-), 6.77 (d, J 9.0, 2H, anilino-H), 7.6-7.9 (m, 4H, anilino-H and isophthalate Ar-H), 8.28 (s, 1 H, isophthalate Ar-H); vmax/cm-l 1730 (-C=O), 1130 (-SO2-); m/z 519 (M+), 406 [M+ -(C8H17)], 342 [M+ -(S02C&17)], 3 10 [+CH2CH2N(CH,)-phenyl-S02C8H17], 133 [+CH2CH2N (CH, )-phenyl] , 1 1 9 [+ CH2N(CH, )-phen yl ], 105 [+N(CH,)-phenyl], 71 (C5Hll+], 57 (C,H,+), 43 (C3H7+), 29 (C2H5').(Found: C, 62.4; H, 7.3; N, 2.55; S, 6.3. Calc. for C2,H3,N07S: C, 62.41; H, 7.18; N, 2.70; S, 6.17%); Amax( CHCl,)/nm (~/lmol -cm -'), 282 (3 1 640); ~,,,off/nm, 337. 5-Substituted isophthalic acid derivatives (13-16) A typical procedure is as follows. Isophthalate 9 (LOOg, 1.21mmol) and sodium hydroxide (0.242 g, 6.0 mmol) were dissolved in methanol (3 m1)-THF (3 m1)-water (3 ml). The mixture was refluxed for 3 h and then allowed to cool, Hydrochloric acid was added to the reaction mixture until the supernatant solution was slightly acidic.The precipitate was collected by filtration. Recrystallization from acetone- water gave 5-{ 2-[N-methyl-4-(perfluorooctylsulfony1)anilino] ethoxy}isophthalic acid (13) (0.819 g, 85%); 6,(CDCl, + [2H6]DMSO; 90 MHz) 3.23 (s, 3 H, -N-CH,), 3.8-4.1 (m, 2H, -N-CH2-), 4.2-4.5 (m, 2H, -0-CH2-), 6.87 (d, J 9.2, 2 H, anilino-H), 7.5-8.0 (m, 4 H, anilino-H and isophthal- ate Ar-H), 8.29 (s, 1 H, isophthalate Ar-H); vmax/cm-l 3445 (carboxylic -OH), 1705 (-C=O), 1245 and 1215 (perfluoro- alkyl), 1155 (-SO2-); m/z 797 (M'), 616 (M'- [OPh (c00H)21>, 378 rM+ -(GFI~)I, 314 [M' -(S02CfjF17)1, 169 [CF3CF2)2+], 119 [CF3CF2' or PhN(CH3)CH2+], 69 (CF,'). (Found: C, 37.4; H, 1.8; N, 1.7.Calc. for C~~H~~NO~FI~S:C, 37.66; H, 2.02; N, 1.77%). Compounds 14-16 were prepared by a similar method as for the preparation of 13 using 10-12 as the raw materials instead of 9, respectively. Compound 14 (86%); dH(CDC1, + [2H6]DMS0, 90 MHz) 1.9-2.3 (m, 4 H, piperidinyl-H), 3.5-3.9 (m, 4 H, piperidinyl- J. Mater. Chern., 1996, 6(5), 711-717 713 H), 4.7-5.0 (m, 1 H, piperidinyl-H), 7.05 (d, J 9.2, 2 H, anilino-H), 7.6-7.9 (d, 4 H, anilino-H isophthalate Ar-H), 8.24 (s, 1 H, isophthalate Ar-H); v,,/cm- 3440 (carboxylic -OH), 1700 (-C =0),1240 and 1220 (perfluoroalkyl), 1160 (-SO, -); W/Z 823 (M'), 642 {M+-[OPh(COOH),]), 404 [M' -(c8F17)], 340 [M' -(S02c&,7)], 182, 169 [CF,(CF,),+], 119 (CF3CF2'), 69 (CF,').(Found: C, 39.6; H, 1.9; N, 1.6. Calc. for C,7H18N07F,7S: C, 39.38; H, 2.20; N, 1.70%). Compound 15 (68%); &(CDCl, +C2H6]DMSO; 90 MHz) 1.2-1.7 (m, 3 H, piperidinyl-H), 1.7-2.2 (m, 4 H, piperidinyl- H), 2.8-3.4 (m, 2 H, -CCH,-piperidine), 3.9-4.4 (m, 4 H, -0-CH2-and 2 x piperidinyl-H), 7.00 (d, J 9.2, 2 H, anilino-H), 7.6-7.9 (m, 4 H, anilino-H and isophthalate-H), 8.20 (s, 1H, isophthalate-H); v,x/cm-l 3430 (carboxylic -OH), 1700 (-C=O), 1240 and 1220 (perfluoroalkyl), 1160 (-SO,-) m/z 851 (M+), 670 (M+-[OPh(COOH),]}, 432 [M+ -(CsF17], 368 [M+ -(SO,C,F17)], 182, 169 [CF3(CF2),+], 119 (CF3CF2'), 69 (CF,'). (Found: C, 40.9; H, 2.4; N, 1.5. Calc. for C2,H,,N07F17S: C, 40.90; H, 2.60; N, 1.64%). Compound 16(69%); 6,(CDCl,; 90 MHz) 0.7-1.9 [m, 15 H, Cfi,(CH,)6CH2-), 2.9-3.3 (m, 2 H, -CH2-S02-, over-lapped by a singlet signal at 6 3.16), 3.16 (s, 3 H, -N-CH,), 3.7-4.2 (m, 2 H, -N-CHI-), 4.2-4.5 (m, 2 H, -0-CH,-), 6.78 (d, J 9.0, 2 H, anilino-H), 7.6-7.9 (m, 4 H, anilino-H and isophthalate Ar-H), 8.32 (s, 1 H, isophthalate Ar-H); v,,x/cm-l 3430 (carboxylic -OH), 1700 (-C=O), 1120 (-SO2-); m/z 491 (M'), 378 [M' -(c'H17)], 330 [M' -(SozCsH17)], 133 [+CH2CH2N(CH3)- Ph], 119 [+CH2N(CH3)- Ph], 105 ['N(CH,)-Ph], 71 (C5Hll'), 57 (C4H9'), 43 (C3H7'), 29 (C2H5') (Found: C, 61.0; H, 6.9; N, 2.85; S, 6.6.Calc. for C25H33N07S: C, 61.08; H, 6.77; N, 2.85; S, 6.52%). 2-[N-(2-H ydroxyethyl )-44 perfluorooctylsulfon yl )anilino] ethanol (17) Compound 17 (76%) was prepared by a similar method as for the preparation of 5 using diethanolamine as the raw material, mp, 113°C (determined from the DSC thermogram); 6,(CDC13; 90 MHz) 2.6-2.8 (brs, 2 H, -OH), 3.6-4.2 (m, 8 H, -N-CH2-), 6.80 (d, J 9.2, 2 H, Ar-H), 7.78 (d, J 9.2, 2 H, Ar-H); v,,,/cm-' 3335 (-OH), 1230 and 1215 (perfluoro- alkyl), 1160 (-SO2-); m/z 663 (M'), 632 [M+-(CH,OH)], 244 [M+ -(cgF17)], 180 [M' -(S02CsF17)], 169 [CF,(CF,),'], 149 [Ph-N(CH2')CH2CH20H], 119 (CF3CF2'), 69 (CF,'). (Found: C, 32.4; H, 1.8; N, 1.9.Calc. for C18H14N04F17S: C, 32.59; H, 2.13; N, 2.11%); Amax(CHC13)/nm(~/1mol-l cm-l), 311 (38 090); ;lcUtoff/nm, 362. General procedure for polymerization All polyesters were prepared by the same procedures. The preparation of Pl is given as a representative example. Under an argon atmosphere, 13 (0.399 g, 0.50 mmol), 17 (0.332 g, 0.50mmol) and triphenylphosphine (0.3 15 g, 1.20 mmol) were dissolved in dry DMSO (0.5 ml) and maintained at 50°C.To this solution diethyl azodicarboxylate (0.204 g, 1.20 mmol) was added. The reaction mixture was stirred at 100 "C for 12 h and then poured into methanol (100 cm3). The precipitate produced was collected by filtration and reprecipitated in a THF-methanol system. Finally, the product was dried in U~CUOto give polymer P1 (0.225 g, 32%); 6,(CDC13; 90 MHz) 3.17 (s, 3 H), 3.7-4.1 (m, 6 H), 4.1-4.3 (m, 6 H), 6.6-7.1 (m, 4 H), 7.4-8.1 (m, 7 H); vm,x/cm-l 2960, 1730 (-C=O), 1590, 1560, 1510,1450, 1390, 1360, 1330, 1310, 1250 (perfluoroalkyl), 1220 (perfluoroalkyl), 1160 (-SO2 -), 1080, 1060, 1000, 910, 860, 820, 760, 710, 650, 580, 560, 530.'H NMR and IR spectral data and yields for the polyesters obtained are as follows. 714 J. Muter. Chem., 1996, 6(5),711-717 P2 (53%); GH(CDC1,; 90MHz) 1.1-1.5 (m, 4 H), 1.8-2.3 (m, 4 H), 3.3-4.3 (m, 5 H), 4.5-4.8 (m, 4 H), 6.5-7.2 (m, 4 H), 7.5-8.2 (m, 7 H); vrnax/cm-' 2930, 2850, 1730 (-C=O), 1590, 1510, 1450, 1390, 1360, 1330, 1310, 1250 (perfluoroalkyl), 1220 (perfluoroalkyl), 1160 (-SO2 -), 1090, 1030, 1000, 860, 820, 760, 710, 650, 580, 550, 530. P3 (56%); h~(cDC1,; 90 MHz) 1.1-1.5 (m, 3 H), 1.8-2.3 (m, 4 H), 2.8-3.3 (m, 2 H), 3.3-4.3 (m, 8 H), 4.5-4.8 (m, 4 H), 6.9-7.2 (m, 4 H), 7.6-8.2 (m, 7 H); vm,x/cm-l 2930, 2850, 1730 (-C=O), 1590, 1510, 1460, 1390, 1360, 1330, 1310, 1250 (perfluoroalkyl), 1220 (perfluoroalkyl), 1160 (-SO2-), 1090, 1030, 860, 820, 760, 710, 650, 580, 550, 530.P4(67%) 6,(CDC13; 90 MHz) 0.8-1.9 (m, 17 H), 2.9-3.1 (m, 2 H), 3.09 (s, 3 H), 2.8-3.3 (m, 2 H), 3.7-4.8 (m, 10 H), 6.8-7.2 (m, 4 H), 7.5-8.1 (m, 7 H); vmaX/cm-' 3090, 2930, 2860, 1730 (-C=O), 1590, 1510, 1460, 1380, 1360, 1330, 1310, 1240 (perfluoroalkyl), 1150 (-SO2 -), 1090, 1060, 1000, 910, 820, 780, 760, 720, 710, 650, 590, 560, 530. SHG measurements First, the polymer was deposited on an ordinary cover glass by spin-coating at a rate of 2000 rpm from a 5 wt% THF solution. The poling procedure for a spin-coated film was achieved by poling normal to the surface by corona discharge.The distance of the tungsten needle from the surface was 25mm. The needle side was set to 10 kV negative to an aluminium heating plate. A spin-coated film of the polyester on a cover glass substrate was heated on an aluminium plate connected to a heater. After 20min of poling around q,the spin-coated film was cooled down to ambient temperature with continuous poling. The SHG activities of the polyesters were measured in transmission by means of the Maker fringe method.49 The experimental apparatus used for the Maker fringe measurement was shown in a previous report." The exciting light source was a Q-switched Nd:YAG laser (Spectron SL404G, A= 1064 nm, 10 Hz repetition rate, 6 ns pulse duration) with its pulse energy less than 1 mJ.The sample was placed on a rotating stage and rotated around a horizontal axis from an incident angle of -80" to +80". SHG signals detected by a photomultiplier were integrated with a boxcar integrator (Stanford Research SR-250). The p-polarized laser beam was chosen using a ;1/4 wave plate and a linear polarizer. Determination of non-linear optical coefficients The second-order NLO coefficients, d33, of the polyesters obtained were determined from the relationship between the SH light intensity and the incident angle of the exciting beam obtained by the Maker fringe method." The d33values of the resulting polyesters were determined by applying the mean square method to eqn. (1) proposed by Jerphagnon et where I,, is the intensity of the SH wave in the uniaxial poled materials generated by the p-polarized exciting wave, the intensity of which is represented by I,, c is the light velocity, w the spot radius of the Gaussian beam, 8 the incident angle of an exciting wave, t, and q,Fresnel-like transmission factors, n, and n2, the refractive indices, R(8) the multiple reflection correction, p(8) a projection factor', B(8) the beam size correction, and Y(8)the angular dependence of the SH power.1 mm Thick y-cut quartz (dll=0.5 pm V-l) was used as a reference sample. Results and Discussion Synthesis of polyesters containing a high density of NLO-active chromophores The synthetic routes to the 5-substituted isophthalic acid derivatives 13-16 and 2-[N-( 2-hydroxyethyl)-4-( perfluorooct- ylsulfonyl)anilino] ethanol (17),which are precursors for the preparation of the polyesters, are shown in Scheme 2.4-Fluorophenyl sulfide derivatives 1 and 2 were prepared by a modification of the method of Feiring et The oxidation of 1 and 2 was carried out using hydrogen peroxide as the oxidative reagent instead of chromium oxide as applied by Feiring et al. in acetic acid. These oxidations proceeded with good yields of over 80%. 5-Substituted isophthalic acid derivatives were prepared by the Mitsunobu reaction between dimethyl 5-hydroxyisophthalate and hydroxy-functionalized chromophores, followed by the hydrolysis of the corresponding dimethyl isophthalate derivatives. All these reactions provided 5-substituted isophthalic acid derivatives in favourable yields.Scheme 1 shows the preparation of polyesters containing a high density of NLO-active chromophores. All of the polyesters were prepared by solution polycondensation of the above isophthalic acid derivatives 13-16 and 2-[N-(2-hydroxyethy1)-4-(perfluorooctylsulfony1)anilino] ethanol (17) in DMSO at 100"C using triphenylphosphine and diethyl azodicarboxylate as the condensation reagents. Pouring the reaction solution into methanol provided 30-70% of the polyesters as colourless powders. Polyesters Pl-P4 are soluble in common polar organic solvents, such as THF, DMF, DMSO and l-methyl- Mil, ixI 14,15 pyrrolidin-2-one (NMP) at room temperature, and slightly soluble in acetone or ethyl acetate but insoluble in methanol or ethanol.The aliphatic components in the backbone are expected to improve the solubility of these polyesters. Optical- quality thin films can be easily obtained by spin-coating from THF solutions of polyesters Pl-P3.However, polyester P4 containing octylsulfonyl moieties in the side chain formed a turbid thin film by spin-coating from the THF solution. This finding may be attributed to the aggregation of the side-chain octyl groups. Table 1 summarizes the results of the elemental analyses and the general characteristics of the resulting polyesters. The results of the elemental analyses agree with the structure of polyesters shown in Scheme 1. The weight-average molecular weights of polyesters estimated from GPC indicate the degree of polymerization was cu.10. DSC thermograms for Pl-P4 are shown in Fig. 1. In each DSC thermogram, a glass trans- ition was observed, however, no other endothermic or exother- mic peaks appeared between 20 and 200°C. The qs of polyesters, which were determined from a second heating scan in the DSC measurements, were in the range of 80 to 99°C as shown in Table 1. These relatively low qs are detrimental to the stabilization of noncentrosymmetric chromophore-align- ment, and are attributed to the incorporated perfluoroalkyl or alkyl group which would increase the free volume around the polymer linkage. There was no significant difference in q between P1 and P4,which indicates that the incorporation of the octyl moiety as a side-chain terminal group instead of a perfluorooctyl one exerts no significant effect on q.P3 exhib-9,12 tvfirt ix 0 13,16 Scheme 2 Reagents: i, NaH-DMF; ii, F(CF2)gI-or H(CH,),Br-DMF; iii, H,O,-CH,COOH; iv, diethanolamine-K,CO,-DMSO; v, N-methylethanolamine-K~C03-DMSO; vi, 4-hydroxypiperidine- or 4-(2-hydroxyethy1)piperidine-K,CO3-DMSO;vii, dimethyl 5-hydroxyiso- phthalate-PPh,-diethyl azodicarboxylate-THF; viii, NaOH-H,O-CH,OH-THF ix, aq.HC1 Table 1 Results of the elemental analyses and characterization of polyesters Pl-P4 results of elemental analyses (YO) polymer C H N MW" hf-fwIM,b ly3Cc PI Calc.36.25 1.84 1.97 9 850 1.26 83 Found 36.3 1.7 1.2 P2 Calc. 37.26 1.95 1.93 11 100 1.28 99 Found 37.5 1.8 2.5 P3 Calc.38.27 2.19 1.90 9 600 1.25 86 Found 38.3 2.0 2.55 P4 Calc. 46.16 3.87 2.50 9 390 1.65 80 Found 46.3 3.9 2.7 "Values estimated from GPC using polystyrene standards. bPolydispersity index. 'Values determined from DSC on a second heating scan. J. Muter. Chem., 1996, 6(5),711-717 715 0 50 100 150 20 TI"C Fig. 1 DSC traces on a second heating scan at a rate of 10 "Cmin and a helium flow rate of 20 ml min ',(a) P1, (b)P2, (c) P3, (d) P4 ited the highest in the present system, because P3 contains the bulky piperidinyl moiety near-around the polymer back- bone Fig 2 shows a typical X-ray diffraction pattern of the polyesters carried out by the powder method at various temperatures There were no diffraction peaks except for a broad halo around 18" in the diffraction pattern of P1 Similar diffraction patterns were obtained for polyesters P2-P4 The lack of optical anisotropy of the present polyesters was con- firmed by polarized microscopic observations at various tem- peratures Thus, the polyesters obtained are concluded to be amorphous UV-VIS spectroscopy and SHG measurement Fig 3 shows the UV-VIS absorption spectrum of P1 as a spin- coated film (thickness <1 pm) on a quartz glass substrate The UV-VIS spectral data are summarized in Table 2 We defined the cutoff wavelength as the wavelength where the value of the c v)C CIG 1 1 rJ 0 10 20 30 2fNdegrees Fig.2 X-Ray diffraction patterns of P1 obtained by the powder method at various temperatures Table 2 Optical properties of polyesters Pl-P4 polymer &,,,/nm A,,,,ff/nm poling temp /"C d,,/pm V P1 307 390 80 30 P2 308 397 90 18 P3 308 391 80 31 P4 321 430 100 34 716 J Muter Chem, 1996,6(5), 711-717 300 400 500 600 3L Inm Fig.3 Typical example of a UV-VIS absorption spectrum of a spin- coated film of P1 first deviation for absorbance becomes 0 When the film- thickness was <1 pm, the present polyesters Pl-P3 exhibited a cutoff wavelength <400 nm, which is desirable for practical use However, Amax and Acutoff of a thin film of P4 were longer than those of Pl-P3 This result is due to the scattering of the incident light, since a turbid thin film is obtained by spin- coating and since A,,, and icutoffof 12, ze the precursor of P4, are shorter than those of 9-11, z e the precursors of Pl-P3, respectively (see Experimental section) Fig 4 shows the relationship between SH light intensity and the incident angle of the exciting beam for a spin-coated film of P4 after corona poling treatment It was confirmed that similar Maker-fringe patterns were obtained for spin-coated films of Pl-P3 after corona poling treatment The calculated second-order NLO coefficients, d33,are sum- marized in Table 2 The present polyesters exhibited d33values of 18-3 4 pm V-' P4 provides a turbid film by spin-coating from a THF solution, however, it exhibited almost the same d,, value as those of P1 and P3 Clays et have reported that the second-order NLO susceptibility, x(2)zzz, of a Langmuir-Blodgett (LB) film composed of an acrylate polymer containing a similar chromophore, N,N-dialkyl-4-(perfluoro-decy1)anilino moiety (p=9 x esu), is estimated to be 3 pm V-' for an exciting wavelength of 1907 nm using the free gas approximation On using a relationship5' of x(2)zzz=2d33, I 0.4 # Y 8? 0\ c 0.2 v,SF I 0.0 f I I I I L -80 -60 -40 -20 0 20 40 60 80 incident anglejdegrees Fig. 4 Relationship between SH light intensity and the incident angle of the exciting beam for a spin-coated film of P4 after heating with corona poling the x(2)zzzvalues of the present polyesters can be estimated to be 3 6-6 8 pm V-l for an exciting wavelength of 1064 nm The use of different exciting wavelengths has been shown to result in different x(2)zz values Therefore, the f2)-values in these cases cannot be directly compared, however, the x(2)zzzvalues in the present system appear to be of a similar magnitude to that of a highly-ordered LB film composed of an acrylate polymer as estimated by Clays et ul Detailed studies on the alignment of chromophores and the stability of chromophore orientation will be the subject of future studies 17 18 19 20 21 22 M Chen, L R Dalton, L P Yu, Y Q Shi and W H Steier, Macromolecules, 1992,25,4032 C Z Xu, B Wu, L R Dalton, P M Ranon, Y Q Shi and W H Steier, Macromolecules, 1992, 25,6714 P Kitipichai, R La Peruta, G M Korenowski and G E Wnek, J Polym Sci ,Polym Chem Ed, 1993,31,1365 P M Ranon, Y Q Shi, W H Steier, C Z Xu, B Wu and L R Dalton, Appl Phys Lett, 1993,62,2605 J E Beecher, J M J Frechet, C S Willand, D R Robello and D J Williams, J Am Chem Soc, 1993,115,12216 M Conroy, Z Ah-Adib, P Hodge, D West and T King, J Muter Chem ,1994,4,1 In conclusion, we have achieved the synthesis of novel types of optically transparent polyesters containing a high density of second-order NLO active chromophores, which were obtained by condensation polymerization between isophthalic acid derivatives and 2-[N-(2-hydroxyethyl)-4-( perfluorooctyl- sulfonyl)anilino] ethanol The amorphous polyesters obtained exhibited good solubility in common organic solvents and a cutoff wavelength shorter than 400 nm Spin-coating from a THF solution of the polyesters provided optical-quality films The SHG measurements of the poled films of the polyesters using a Q-switched Nd YAG laser (1064 nm) as the exciting beam showed that the present polyesters exhibited second- order NLO coefficients, d33, in the range of 1 8-3 4 pm V-' 23 24 25 26 27 28 29 30 J E Beecher, T Durst, J M J Frechet, A Godt and C S Willand, Macromolecules, 1994,27, 3472 N P Wang, T M Laslie, S P Wang and S T Kowel, Chem Muter, 1995,7, 185 J D Stenger-Smith, J W Fischer, R A Henry, J M Hoover, M P Nadler, R A Nissan and G A Lindsay, J Polym Sci Polym Chem Ed, 1991,29,1623 F Fuso, A B Padias and H K Hall, Macromolecules, 1991, 24, 1710 M Chen, L P Yu, L R Dalton, Y Q Shi and W H Steier, Macromolecules, 1991,24,5421 G A Lindsay, J D Stenger-Smith, R A Henry, J M Hoover, R A Nissan and K J Wynne, Macromolecules, 1992,25,6075 C Z Xu, B Wu, M W Becker, L R Dalton, P M Ranon, Y Q Shi and W H Steier, Chem Muter, 1993,5, 1439 J Tsibouklis, P H Richardson, A M Ahmed, R W Richards, W J Feast, S J Martin, D D C Bradley and M Warner, Synth The authors acknowledge Mr Toshiki Hagiwara (Sagami Chemical Research Center) for "F NMR measurements 31 Met, 1993,61,159 C V Francis, K M White, R A Newmark and M G Stephens, Macromolecules, 1993,26,4379 32 M E Wright, S Mullick, H S Lackritz and L Y Liu, Macromolecules, 1994,27, 3009 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Non-linear Optical Properties of Organic and Polymeric Materials, ACS Symposium Series 233, ed D J Williams, American Chemical Society, Washington, DC, 1983 Non-linear Optics Materials and Devices, ed C Flytzanis and J L Oudar, Springer-Verlag, Berlin, Heidelberg, New York, Tokyo, 1986 Non-linear Optical Properties of Organic Molecules and Crystals, ed D S Chemla and J Zyss, Academic Press, New York, 1987 Non-linear Optical and Electroactive Polymers, ed P N Prasad and D R Ulrich, Plenum Press, New York, 1988 Materials for Non-linear Optics, Chemical Perspective, ACS Symposium Series 455, ed S R Marder, J E Sohn and G D Stucky, American Chemical Society, Washington, DC, 1991 Organic Molecules for Non-linear Optics and Photonics, NATO AS1 Series, Series E, Applied Science 194, ed J Messier, F Kajzar and P N Prasad, Kluwer Academic Publishers, Dordrecht, 1991 D M Burland, R D Miller and C A Walsh, Chem Rev, 1994, 94,31 K D Singer, J E Sohn and S J Lalama, Appl Phys Lett, 1986, 49,248 J T Lin, M A Hubbard and T J Marks, Chem Mater, 1992, 4,1148 Z Peng and L P Yu, Macromolecules, 1994,27,2638 A K Y Jen, K J Drost, Y Cai, V P Rao and L R Dalton, J Chem Soc ,Chem Commun ,1994,965 A K -Y, Jen, Y J Liu, Y Cai, V P Rao and L R Dalton, J Chem Soc Chem Commun , 1994,2711 W Sotoyama, S Tatsuura and T Yoshimura, Appl Phys Lett, 1994,64,2197 L P Yu, W Chan and Z Bao, Macromolecules, 1992,25, 5609 J D Stenger-Smith, R A Henry, J M Hoover, G A Lindsay, 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 H J Winkelhahn, T K Servay, L Kalvoda, M Schulze, D Neher and G Wegner, Ber Bunsenges Phys Chem , 1993,97,1287 C S Kang, H J Winkelhahn, M Schulze, D Neher and G Wegner, Chem Muter, 1994,6,2159 J L Oudar and D S Chemla, J Chem Phys, 1977,66,2664 J L Oudar and J Zyss, Phys Rev A, 1982,26,2016 A Ulman, C S Wiland, W Kohler, D R Robello, D J Williams and L Handley, J Am Chem SOC ,1990,112,7083 A Hayashi, Y Goto, M Nakayama, K Kaluzynski H Sato, K Kato, K Kondo, T Watanabe and S Miyata, Chem Muter, 1992,4,555 H S Nalwa, T Watanabe, A Kakuta, A Mukoh and S Miyata, Synth Met, 1993,55-57,3895 H S Nalwa, T Watanabe, A Kakuta, A Mukoh and S Miyata, Appl Phys Lett, 1993,62,3223 T Tomono, Y Nishikata, L S Pu, T Sassa, T Kinoshita and K Sasaki, Mol Cryst Liq Cryst, 1993,227,113 K Clays, N J Armstrong, M C Ezenyilimba and T L Penner, Chem Muter, 1993,5,1032 J E Beecher, T Durst, J M J Frechet, A Godt, A Pangborn, D R Robello, C S Willand and D J Williams, Adv Muter, 1993, 5,632 M Kamath, C E Masse, R J Jeng, M Cazecd, X L Jiang, J Kumar and S K Tripathy, J Macromol Sci Chem, 1994, A31,2011 N Nemoto, F Miyata, Y Nagase, J Abe, M Hasegawa and Y Shirai, Macromolecules, in the press A E Feiring, J Fluorine Chem ,1984,24, 191 A E Feiring, E R Wonchoba and S D Arthur, J Polym Sci Polym Chem ,1990,28,2809 0 Mitsunobu, Synthesis, 1980, 1 J Jerphagnon and S K Kurtz, J Appl Phys , 1970,41,1667 N Nemoto, Y Nagase, J Abe, H Matsushima, Y Shirai and N Takamiya, Macromol Chem Phys , 1995,196,2237 M P Nadler and R A Nissan, J Polym Scr ,Polym Chem, 1993, 31,2899 51 P Randou, M Van Beylen, C Samyn, G S'heeren and A Persoons, Macromol Chem Phys ,1992,193,3045 16 C Weder, P Neuenschwander, U W Suter, P Pretre, P Kaatz and P Gunter, Macromolecules, 1994,27,2181 Paper 5/06488K, Recevied 2nd October, 1995 J Muter Chem, 1996, 6(5),711-717 717

ISSN:0959-9428    

DOI:10.1039/JM9960600711

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Chemical modification of monolithic poly (styrene-divinylbenzene) PolyHIPE@ materials Neil R. Cameron,"+ David C. Sherrington,*" Isao Andob and Hiromichi Kurosub "University of Strathclyde, Dept. Pure & Applied Chemistry, 295 Cathedral St., Glasgow, UK, GI 1XL bDept.of Polymer Chemistry, Tokyo Institute of Technology, 0-okayama, Meguro-ku, Tokyo 152, Japan Monolithic samples of highly porous poly(styrene/DVB) PolyHIPE@ have undergone a number of electrophilic aromatic substitution reactions, namely sulfonation, nitration and bromination. Mild, hydrophobic reagents and homogeneous reaction conditions were sought in an effort to achieve uniform chemical modification, to a reasonable degree of substitution, throughout the large polymeric structures. Thus, sulfonation was carried out with lauroyl sulfate in cyclohexane, nitration with tetrabutylammonium nitrate-trifluoroacetic anhydride (TBAN-TFAA) in dichloromethane and bromination with bromine- stannic chloride in dichloromethane. An average degree of sulfonation of 2.4 mmol g-1 was achieved, with a drop in sulfonic acid content of approximately 1mmol g-' from surface to centre. Nitration occurred to a lesser extent, with similar differences in substitution between surface and centre being observed.PolyHIPE@ monolithic samples were brominated to an extent of 3.6 mmol g-' furthermore, this was uniform across the entire substrate. The differences in extent of each reaction are explained by consideration of such factors as the nature of the solvent, polarity of the reagents and compatibility between the reagents and the polymer matrix throughout the reactions.Polymerisation of the continuous phase of a high internal phase emulsion (HIPE), in which the dispersed phase droplets occupy greater than 74% of the total emulsion volume and the continuous phase contains one or more, typically vinyl, monomer, leads to a novel, monolithic, macrocellular material known as PolyHIPE@ 1*2(Fig. 1). These materials are highly porous, with a void volume fraction generally of 0.9, but which can be as high as 0.99. In addition, they usually possess an open cellular structure, in which each cavity is connected to its neighbours. This results in a polymer material of very low density. Styrene-divinylbenzene (DVB) PolyHIPE@ polymers have been studied fairly extensively, and conditions for the control of their cellular str~cture,~ cell size,4 porosity and surface area5 are well documented.The preparation of polymer-supported reagents and catalysts is most commonly achieved via the chemical modification of preformed polymers, and numerous examples have been reported in the chemical literature. Crosslinked polystyrene t Present address: Eindhoven University of Technology, Laboratory of Polymer Chemistry and Technology, Den Dolech 2, PO Box 513, 5600 MB Eindhoven, The Netherlands. Fig. 1 Scanning electron micrograph of poly(styrene-DVB) PolyHIPE@ resins, which have been extensively employed as polymeric support systems, can be chemically modified by e.g.direct electrophilic aromatic substitution of the styrene residues, nucleophilic substitution of chloromethylated polystyrene resins$ and electrophilic substitution of lithiated polystyrene. A vast range of polymer-supported species have been synthesised via these routes.6 There are, however, experimental problems involved in the chemical modification of crosslinked polymer resins. Since the vast majority (>99%) of reactive sites are located in the interior of the polymer particles, the diffusion of reactants to these sites is of paramount importance if a high degree of modification is to be achieved. In the case of gel-type resins, this necessitates the use of reaction solvents which will swell the crosslinked polymer beads.It should also be noted that the polymer must remain swollen throughout the entire reac- tion to ensure continued access of the reagents to the reactive sites. As the reaction proceeds, the swelling properties of the polymer may change drastically. An example of this is in the chemical modification of chloromethylated polystyrene with tertiary amines, generating quaternary ammonium salts. The polymer changes, therefore, from being relatively hydrophobic to possessing highly polar, ionic groups. Even with macrop- orous resins, care can be required in selecting the solvent with which to achieve high levels of functionalisation. In the case of monolithic PolyHIPE@ materials, these diffusion-related problems are greatly exacerbated.The diffusion path-length from external solution to the interior of a polymeric rod can typically be as high as 20-25 mm. Additionally, the relatively large dimensions of the polymer samples require that the reactant solution should equilibrate fully throughout the crosslinked matrix prior to the reaction occurring to any significant extent, in order to achieve uniform chemical modification. A number of conclusions regarding the experimental con- ditions required for uniform chemical modification of mono- lithic PolyHIPE@ samples can therefore be made. First, the $ Owing to the extreme carcinogenicity of chloromethyl ether, nucleophilic substitution of poly(vinylbenzy1 chlonde) resins is more preferable. J. Muter. Chem., 1996, 6(5), 719-726 719 reaction solvent should swell the starting polymer material and, where possible, the polymer should remain swollen during the reaction Second, the reagents themselves should be com- patible with the polymer matrix, and therefore relatively hydro- phobic Third, the reaction conditions should be such that the rate of reaction is low at ambient or ice temperature, allowing equilibration of the reagent solution throughout the polymer, while moderate heating of the system produces a reasonable rate of chemical modification This third point implies that relatively mild reagents are required The aim of this research was to achieve the uniform chemical modification of poly- (styrene-DVB) PolyHIPE@ monolithic samples via electro-philic aromatic substitution, the particular reactions chosen being sulfonation, nitration and bromination With the above requirements in mind, suitable reagents with which to achieve these goals were sought Experimenta1 Materials and instrumentation Styrene (Fisons), DVB (Aldrich, tech grade, 55%), potassium persulfate (Fisons, 97 + YO),calcium chloride hexahydrate (Fisons), sulfuric acid (Fisons, 96%), chlorosulfonic acid (BDH, %'YO), lauric acid (Aldrich, 99 + YO),acetic anhydride (BDH, 98%0), nitric acid (BDH GPR, 69%), trifluoroacetic anhydride (Aldrich, 99 + %), ammonium nitrate (Aldrich, 98 + YO), bromine (BDH, 99"/), stannic chloride (Aldrich, 99%0) and pyridine (Aldrich, 99+%) were used as received Tetrabutylammonium nitrate (Fluka) was recrystallised from ethanol and dichloromethane (Hays Ltd ) was distilled under nitrogen from calcium hydride The surfactant sorbitan monooleate (Span 80, Koch-Light) and all other solvents were used as received Infra-red spectra were recorded on a Mattson 1000 FTIR spectrometer, samples were prepared by crushing and com- pressing into KBr discs C, H and N elemental analyses were carried out simultaneously with a Perkin Elmer 2400 Analyser Halogen and sulfur contents were determined by titration methods Solid state 13C NMR spectra were recorded on a JEOL GSX-270W spectrometer with cross-polarisation and magic angle spinning (CP-MAS) accessories, and employing a total suppression of spinning side-band (TOSS) pulse sequence The peaks were referenced to the higher field peak of ada- mantane, which was set at 29 5 ppm from tetramethylsilane (TMS) All solid state 13C NMR spectra were proton-decoupled and recorded at 67 8 MHz NMR measurements were performed in the Department of Polymer Chemistry, Tokyo Institute of Technology, Japan PolyHIPE@ coding system The PolyHIPE@ matenals described in this article are classified by a code, which is dependent on the crosslink density and pore volume of the polymer The codes for the poly (styrene-DVB) systems have the general form XaPV b, where X is the nominal crosslink density (% of actual divi- nylbenzene isomers used) and PV is the pore volume (YOV/V of aqueous solution used as the internal phase during PolyHIPE@ preparation) Thus X2OPV90 would represent a poly(styrene-DVB) PolyHIPE@ material of approx 20% crosslinker content and 90% pore volume PolyHIPE@ preparation The example given here is for a poly(styrene-DVB) material of 90% porosity and crosslink density of approximately 5% These values are changed by altering the aqueous to organic phase ratio, and the DVB to styrene ratio, respectively Styrene (22 5 ml, 0 2 mol), DVB (2 5 ml, ca 10 mmol) and Span 80 (50 g) were placed in a 300 ml wide-necked polyethyl- 720 J Muter Chem , 1996, 6(5), 719-726 ene bottle The mixture was stirred with a glass rod fitted with a D-shaped PTFE paddle, connected to an overhead stirrer motor, at approx 300 rpm Plastic film was stretched over the neck of the container to reduce monomer evaporation The aqueous phase was prepared separately by dissolving potassium persulfate (0 5 g, 18 mmol) and calcium chloride hexahydrate (2 5 g, 10 mmol) in distilled water (225 ml) Ths was added, dropwise, with constant mechanical stirring, to the organic solution As the aqueous phase was added, the bottle was lowered to maintain stirring just below the surface of the developing HIPE, ensuring that no water pockets formed Once all the aqueous phase had been added, stirring was continued for a further 5 min, to produce as uniform an emulsion as possible The stirrer was then removed and the bottle was sealed The HIPE was polymerised by immersing the plastic bottle in a water bath, thermostatted at 65 "C, for 48 h The container was then cut away from the resulting polymer monolith, which was extracted in a Soxhlet apparatus with water, for 24 h, to remove inorganic materials, followed by a lower alcohol, for a further 48 h The bulk of the liquid was removed from the porous material zn vacuo at room temperature, and drying was completed zn uucuo at 50 "C for 24 h PolyHIPE@ preparation in polymerisation mould To eliminate unnecessary wastage of plastic bottles, a cylindri- cal PVC PolyHIPE@ polymerisation mould was designed This came in the form of two halves, which were screwed together, with separate screw-on base and lid When assembled, the mould had an internal height of 14cm and an internal diameter of 4 5 cm Pnor to use, the inner surfaces were sprayed with PTFE spray to prevent the polymer from adhering to the mould The HIPE was prepared as above, in a plastic bottle, and was subsequently poured into the assembled mould, no sealing of the seams was required The mould was then immersed in a water bath as above, to form the PolyHIPE@ The polymer monolith could easily be retrieved from the disassembled vessel, and was washed and dried as above Sulfonation Small scale reactions.Acetyl suEfate Acetyl sulfate (1) was prepared prior to each experiment Acetic anhydride (15 4 ml, 0 16 mol) was added to 1,2-dichloroethane (DCE) (39 6 ml), and the solution was cooled to below 10°C in an ice bath Sulfuric acid (5 6 ml, 0 10mol) was then added, resulting in a clear solution of 16 mol 1-1 acetyl sulfate in DCE (assuming quantitative reaction) A small cube (approx 2cm per side) of poly(styrene-DVB) PolyHIPE@ (X2OPV90) (0 59 g, ca 3 4 mmol Ph groups) was placed in a three-necked 100 ml round-bottomed flask fitted with a rubber septum This was evacuated, to aid liquid penetration into the porous polymer, and acetyl sulfate in DCE (6 0 ml) was introduced uza syringe The impregnated PolyHIPE@ cube was heated at 70-75 "C for 24 h, after which it was extracted with isopropyl alcohol in a Soxhlet apparatus for 24 h It was dried in uacuo at 50°C for a further 24 h Mass of product =O 79 g Microanalysis surface sample C, 63 4, H, 6 0, S, 6 9%, gives 2 2 mmol (S0,H) 8-l Centre sample C, 678, H, 63, S, 62%, gives 19mmol (S03H)g-', FTIR v/cm-' 3387 (OH str), 3030, 2940, 1600, 1191 (S=O str), 706 (C-S str) Lauroyl sulfate Lauroyl sulfate (2) was also prepared prior to each sulfonation Lauric acid (8 01 g, 40 0 mmol) was dis- solved in cyclohexane (10 8 ml) in a three-necked 100 ml round-bottomed flask with magnetic stirring, under nitrogen Chlorosulfonic acid (17 ml, 25 0 mmol) was added, and stirring was continued at 25 "C for 1h A 2 cm side cube of poly(styrene-DVB) PolyHIPE* (X5PV90) (0 85 g, ca 73mmol Ph groups) was evacuated in a three-necked 100 ml round-bottomed flask, fitted with a rubber septum.The lauroyl sulfate solution was subsequently transferred to the flask via syringe, and the flask was heated at 50°C for 24 h. The PolyHIPE@ was then removed and extracted with light petroleum (bp 60430°C) in a Soxhlet apparatus for 48 h and dried in uucuo at 50°C for 24 h.Mass of product = 1.66 g. Microanalysis: surface sample: C, 36.8; H, 4.4; S, 13.0% gives 4.0 mmol (S03H) 8-l. Centre sample: C, 48.2; H, 5.5; S, 10.2% S, gives 3.2 mmol (SO,H) 8-l. Large scale reactions. Lauroyl sulfate. Lauroyl sulfate (2) in cyclohexane was prepared as above. Chlorosulfonic acid (16.0m1, 0.24mol) was added to a solution of lauric acid (78.6 g, 0.39 mol) in cyclohexane (134 ml) at 25 "C, and the resulting solution was stirred at 25°C for 1 h. A PolyHIPE@ monolith (X2OPV90) (15.2 g, ca. 0.1 mol Ph groups), of 10.3 cm height and 4.5 cm diameter, was placed in a round-bottomed glass reactor vessel fitted with a ground-glass flange.The reactor was evacuated for approx. 1 h then sealed, after which the solution of lauroyl sulfate in cyclohexane was introduced with the vessel still under vacuum. The solution was allowed to equilibrate throughout the PolyHIPE@ porous structure; following this, the vessel was immersed in a water bath thermostatted at 55°C for 48 h. The monolithic product was then extracted with cyclohexane in a large Soxhlet apparatus for 96 h, and was dried under reduced pressure at room temperature, and finally in uucuo at 50 "C for 24 h. Mass of product =23.0 g. Microanalysis: surface sample: C, 50.2; H, 6.0; S, 8.6%, gives 2.7 mmol (S03H) 8-l; FTIR: v/cm-' 3413 (OH str.), 3030, 2928, 1626, 1191 (S=O str.), 706 (C-S str.); 6, 17.1 (CH,), 29.8 (CH,), 40.6 (CH, CH,), 128.2 (aryl-CH), 138.0 (aryl-C-SO,H), 145.6 (aryl-C).Nitration Small scale reactions. Nitric acid-sulfuric acid. Two small cubes (approx. 5 mm per side) of poly(styrene-DVB) PolyHIPE@ (X5PV90) (0.15g, ca. 1.3 mmol Ph groups) were placed in a 50 ml round-bottomed flask, which was cooled in an ice bath. A 2: 1 mixture of sulfuric and nitric acids (3.5 ml), previously cooled to ice temperature, was added at atmospheric pressure, and the flask was maintained at ice temperature for a further 2 h. It was gradually allowed to warm to room temperature and left for a total of 24 h. Following this, the polymer sample was immersed in approximately 200 ml of ice- water and left for 16 h, then extracted with de-ionised water in a Soxhlet apparatus until the pH of the washings was neutral (72 h).The product was further extracted with ethanol for 3 h, then diethyl ether for 16 h, and was dried in uacuo at 50 "C for 24 h. Mass of product =0.24 g. Microanalysis: C, 52.9; H, 3.5; N, 12.1, gives 8.6 mmol (NO,) 8-l; FTIR: v/cm-' 3089, 2935, 2870, 1615, 1534 (NO, asym. str.), 1355 (NO, sym. str.), 856 (aryl C-N str.), 834, 747, 704. Nitric acid-sulfuric acid-DMF. Poly(styrene-DVB) PolyHIPE@ (X5PV90) (0.14 g, ca. 1.2 mmol Ph groups), in the form of small cubes (approx. 5 mm per side), was placed in a 50 ml round-bottomed flask, and DMF (3 ml) was added at atmospheric pressure. The flask was placed in an ice bath, and the polymer was left to swell for about 1 h.The nitrating mixture (H,SO,-HNO,, 2: 1) (3.5 ml), pre-cooled in an ice bath, was added, and the temperature was allowed to increase to ambient. The reaction was left at room temperature for 60 h, after which the polymer was washed and dried as above. Mass of product =0.14 g. Microanalysis: C, 73.0; H, 4.9; N, 5.9%, gives 4.2 mmol (NO,) 8-l. Nitric acid-sulfuric acid-Kinetic Study. Poly(styrene-DVB) PolyHIPE* (X5PV90) (0.39 g, ca. 3.4 mmol Ph groups), in the form of small cubes (approx. 5 mm per side), was placed in a 100 ml round-bottomed flask, which was cooled in an ice bath. A mixture of sulfuric and nitric acids (2 :1) (9 ml), pre-cooled to ice temperature, was added at atmospheric pressure, and the flask was allowed to come to room temperature over a period of about 2 h.A small cube of PolyHIPE@ was removed at certain time intervals (1, 2, 4, 10 and 24 h) and immersed in a 1 moll-' NaOH solution for 6 h. Each polymer sample was then placed in a beaker of distilled water; the water was decanted and replaced until the pH remained neutral. Samples were then immersed in ethanol for at least 6 h, after which they were dried in uucuo at 50 "C for 24 h. The extent of nitration was determined by microanalysis. Total mass of product =0.61 g. Ammonium nitrate-triJluoroacetic anhydride. Small cubes (approx. 5 mm per side) of poly(styrene-DVB) PolyHIPE@ (X5PV90) (0.51 g, ca. 4.4 mmol Ph groups) and ammonium nitrate (0.36 g, 4.5 mmol) were placed in a three-necked 100 ml round-bottomed flask, to which trifluoroacetic anhydride (3.3 g, 15.7 mmol) and chloroform (20 ml) were added at atmospheric pressure. The flask was fitted with a reflux con- denser and anhydrous calcium chloride drying tube, and the reaction mixture was kept at room temperature for 24 h, then refluxed for 24 h.The polymer was removed, extracted with chloroform for 24 h, then ethanol for a further 24 h, and was dried under reduced pressure at room temperature, and finally in uucuo at 50°C for 24 h. Mass of product=0.56 g. Microanalysis: C, 79.0; H, 4.9; N, 3.0%, gives 2.1 mmol (N0,)g-'; FTIR: v/cm-l 3063, 3037, 2922, 2858, 1604, 1529 (NO, asym. str.), 1355 (NO, sym. str.), 856 (aryl C-N str.), 758. 703. Tetrabutylammonium nitrate-trijluoroacetic anhydride.Poly(styrene-DVB) PolyHIPE@ (X5PV90) (0.57 g, ca. 4.9 mmol Ph groups), again as cubes of approximately 5mm per side, was placed in a three-necked 100ml round- bottomed flask. Tetrabutylammonium nitrate ( 1.61 g, 5.3 mmol) was dissolved in dichloromethane (DCM) (20 ml); the resulting solution, along with trifluoroacetic anhydride (3.3 g, 15.7mmol), was added to the flask at atmospheric pressure, which was subsequently fitted with a reflux condenser. This was carried out under a stream of N, gas. The flask was heated at 30°C for 24 h, under N,, after which the polymer was removed and immersed in fresh DCM and left for 16 h. The product was then extracted in a Soxhlet apparatus with ethanol for 24 h, and was dried in uucuo at 50°C for 24 h.Mass of product=0.68 g. Microanalysis: C, 65.3; H, 5.5; N, 5.9, gives 4.2mmol (NO,) g-'; FTIR: v/cm-' 3086, 3028, 2924, 2855, 1600, 1523 (NO, asym. str.), 1352 (NO, sym. str.), 859 (aryl C-N str.), 755, 704; 6, 40.9 (CH, CH?), 128.1 (aryl-CH), 146.8 (aryl-C-NO,), 153.0 (aryl-C). Large scale reactions. Nitric acid-sulfuric acid. A 2 :1 mixture of sulfuric and nitric acids (l00ml) was added to a round- bottomed glass reactor with a ground-glass flange, fitted with a vacuum outlet and a rubber septum. A poly(styrene-DVB) monolithic sample (X5PV90) (2.35 g, ca. 0.02 mol Ph groups), of 45 mm diameter and 22 mm height, was suspended above the nitrating solution via a knife-blade attached to a glass rod, which had been pushed through the rubber septum.The reactor was then immersed in an ice bath and evacuated for 1 h. The PolyHIPE@ sample was then lowered into the acid mixture by pushing the glass rod through the rubber septum, and the vessel was quickly repressurised. In this manner, the reagents would be forced into the evacuated interior of the porous material. The reactor was initially left in the ice bath, which was allowed to warm to room temperature, and was further left at ambient temperature for 24 h. The PolyHIPE@ macrosample was then extracted in a large Soxhlet apparatus with water, until the pH of the washing water was neutral, J. Muter. Chem., 1996, 6(5),719-726 721 then with ethanol for 48 h It was allowed to dry on the open bench, and was further dried zn uucuo at 50°C for 72 h Mass of product =3 19 g Microanalysis surface sample C, 56 3, H, 4 1, N, 11 1% N, gives 7 9 mmol (NO,) g-', FTIR v/crn-' 3101,2935,2870,1615, 1534 (NO, asym str), 1349 (NO, sym str ), 863 (aryl C-N str ), 747, 712 Tetrabutylammonium nitrate-trzjcluoroacetic anhydride Tetrabutylammonium nitrate (12 3 g, 0 04 mol) was dissolved in DCM (200 ml), and the solution was placed in a round- bottomed glass reactor with a ground-glass flange, fitted with a nitrogen gas inlet Trifluoroacetic anhydride (17 8 g, 0 08 mol) was added under a flow of N, gas, and the solutions were mixed A monolithic sample of poly(styrene-DVB) PolyHIPE@ (X5PV90) (3 93 g, ca 0 03 mol Ph groups), of similar dimen- sions to that used above, was added at atmospheric pressure, and the vessel was heated at 30°C for 24 h under N, gas The polymer cylinder was subsequently removed, cut in half along its diameter, and the pieces were extracted in a Soxhlet apparatus with DCM for 48 h, followed by ethanol for 24 h The product was then dried on the open bench and in uucuo at 50 "C for 24 h Mass of product =4 11 g Microanalysis surface sample C, 80 2, H, 6 7, N, 2 8%, gives 2 0 mmol (NO,) g-', FTIR v/crn-' 3089, 2935, 2858, 1606, 1526 (NO, asym str), 1354 (NO, sym str), 860 (aryl C-N str), 756, 710 Bromination Small scale reactions.Bromine-pyridzne Bromine (093 g, 5 8 mmol) and pyridine (3 drops) were added to chloroform (10 ml) in a 25 ml round-bottomed flask, which had been pre- cooled to ice temperature A red crystalline precipitate quickly formed To this solution was added poly(styrene-DVB) PolyHIPE@ (X5PV90) (0 14 g, ca 1 2 mmol Ph groups), in the form of small cubes of side 5 mm, at atmospheric pressure, and the flask was allowed to warm to room temperature over about 2 h The reaction mixture was then refluxed for 24 h, after which the polymer was extracted in a Soxhlet apparatus with chloroform for 72 h and ethanol for 20 h It was dried in uucuo at 50 "C for 24 h Mass of product =0 16 g Microanalysis C, 67 0, H, 3 2, Br, 26 4%, gives 3 3 mmol (Br) g-', FTIR v/cm-' 3063, 3030, 2922, 2858, 1606, 699 The experiment was repeated (mass of starting polymer= 0 14 g) with chlorobenzene (10ml) as solvent Initially the mixture was homogeneous but a crystalline precipitate appeared after a short while The reaction was warmed to room temperature, then heated at 120 "C for 24 h The polymer product was washed and dried as above Mass of product= 0 13 g Microanalysis C, 69 4, H, 3 7, Br, 24 0%, gives 3 0 mmol (Br) g-' Bromine-stannzc chloride Poly(styrene-DVB) PolyHIPE* (X5PV90) (0 66 g, ca 5 7 mmol Ph groups), as cubes of side 5 mm, was placed in a three-necked 100 ml round-bottomed flask fitted with condenser, nitrogen gas inlet and gas bubbler The system was purged with N, gas for 10 min, after which a solution of bromine (4 0 g, 25 mmol) and stannic chloride (0 04 g, 0 15 mmol) in DCM (30 ml) was added at atmospheric pressure The flask was heated at 35 "C for 24 h, following this, the polymer was extracted in a Soxhlet apparatus with chloro- form for 24 h, then ethanol for 6 h It was dried zn uucuo at 50 "C for 72 h Mass of product =O 87 g Microanalysis C, 59 2, H, 45, Br, 340%, gives 43mmol (Br) g-', FTIR v/cm-' 3055, 3030,2928,2864, 1600,834,760,706,6,40 5 (CH, CH2), 120 2 (aryl-C-Br), 129 8 (aryl-CH), 144 7 (aryl-C) Large scale reactions. Bromine-stannic chloride A mono-lithic sample of poly(styrene-DVB) PolyHIPE'@ (X5PV90) (4 48 g, ca 0 04 mol Ph groups), with a height of 30 mm and a diameter of 45 mm, was placed in a round-bottomed glass 722 J Muter Chem, 1996,6( 5), 719-726 reactor with a ground-glass flange, fitted with a nitrogen gas inlet The vessel and polymer were cooled in an ice-salt bath to between -5 and -10"C, then were evacuated for 1 h and purged with N, gas, twice A solution of bromine (27 9 g, 0 18 mol) and stannic chloride (031 g, 1 19 mmol) in DCM (200ml) was added, a condenser and gas bubbler were fitted, and the reaction mixture was maintained at ice-salt tempera- ture for 2 h, warmed to room temperature over 1 h then heated at 35 "C for 24 h, all under a steady flow of N, The polymer material was then extracted in a large Soxhlet apparatus with chloroform for 20 h and ethanol for 24 h, then dried at reduced pressure at room temperature for 8 h and, finally, in uacuo at 50 "C for 24 h Mass of product = 5 11 g Microanalysis surface sample C, 62 9, H, 4 6, Br, 29 8, gives 3 7 mmol (Br) g-l, FTIR v/cm-' 3063, 3028, 2924, 2855, 1606, 824, 765, 702 Determinationof the chemical modification profiles of monolithic PolyHIPE@ samples The dry polymer cylinders were cut in half to give a circular cross-section Small samples (15-20 mg) were taken radially, at regular intervals, from the centre to the surface, these were submitted for microanalysis to enable the construction of a chemical modification profile across the radius of the PolyHIPE@ monolith Results and Discussion PolyHIPE@ preparation Poly (styrene-DVB)-based PolyHIPE@ materials have received the most attention in the literature The procedure for their preparation described in the Experimental section is the result of optimisation studies previously carried out in this research groups7 In principle, any divinyl crosslinker can be used as long as it is not excessively hydrophilic This property may destabilise the HIPE or cause the species to be solubilised by the aqueous phase The PolyHIPE@ polymerisation mould was designed to prevent wastage of polyethylene bottles and to facilitate mono- lith isolation, as it was envisaged that a large quantity of monoliths would be prepared The internal surfaces of the mould were sprayed with PTFE to allow easy removal of the material after polymerisation Preparation of the HIPE inside the mould was not possible as the joins were not sealed and so leakage would occur However, if formed in a plastic bottle then poured into the mould, the concentrated emulsions are sufficiently viscous to prevent escape Sulfonation The conventional method for the sulfonation of polystyrene macroporous resins is treatment with concentrated sulfuric acid' However, this was anticipated as being unsuitable for uniform sulfonation of large PolyHIPE@ monoliths since H,S04 is a very strong sulfonating reagent, and is not particu- larly compatible with crosslinked polystyrene Other sulfonation reagents previously employed include chlorosulfonic acid in chlorinated solventsg and sulfur triox- ide Mild sulfonation of polystyrene has been achieved with acetyl sulfate (1) in halogenated solvents,12 l3 and Thaleri4 has reported the mild, homogeneous sulfonation of polystyrene with hydrocarbon-soluble acyl sulfates, such as lauroyl sulfate (2) (Scheme 1) Both acetyl and lauroyl sulfate appeared attractive reagents with which to achieve uniform sulfonation of poly (styrene-DVB) PolyHIPE@ macrosamples, and so were investigated further Sulfonation was initially attempted with acetyl sulfate on a small cube of the material, of approximately 2 cm per side The reaction was performed in 1,2-dichloro- SO,H CH,(CH,),CO,H ACH,(CI-4)&O2SO,H 2 Scheme 1 Sulfonation of poly(styrene-DVB) PolyHIPE@ with hydro- philic and hydrophobic reagents.Reagents and conditions: i, H,SO,, DCE, 0-10 "C; ii, ClSO,H, cyclohexane, room temp., 1 h. ethane (DCE), causing the polymer to swell; this would hopefully lead to a high degree of modification. The presence of aromatic sulfonic acid groups in the product is confirmed by a broad -OH stretch peak at 3387 cm-' and the -S=O stretch signal at 1191 cm-' in the FTIR spectrum. The microanalytical data indicate an average sulfonic acid content of 2 mmol g-', almost uniformly throughout the sample.However, this represents a 'yield' of only approximately 35%, based on the quantity of styrene residues (neglecting DVB and ethylvinylbenzene isomers) in the substrate. It was believed that this figure could be improved by employing a more hydrophobic sulfonating reagent which would have a higher compatibility with the polymer matrix. Such a reagent is lauroyl sulfate, which is a member of the same homologous series and possesses a long (Cll) hydro-carbon chain.A sulfonation level of 4 mmol g-' was obtained, which corresponds to about 70% substitution. However, sul- fonation is less homogeneous, with a drop of almost 1 mmol g-' in sulfonic acid content between surface and centre of the cube. This may be due to the lower swelling ability of cyclohex- ane compared to DCE. The higher overall level of sulfonation may also accentuate the differences between interior and exterior sulfonic acid content. Sulfonation of monolithic poly (styrene-DVB) PolyHIPE@ polymers was performed with lauroyl sulfate in cyclohexane. The highly porous material was evacuated for 1 h prior to addition of the reagent solution. It was hoped that this would allow rapid equilibration of the solution throughout the poly- mer substrate, reducing the differences in extent of sulfonation between surface and interior. Aromatic sulfonation was confirmed by FTIR spectroscopy, and additionally by solid state 13C NMR spectroscopy.A peak in the latter spectrum at 6 138, which appeared as a shoulder on the high field side of the aryl quaternary carbon peak at 6 145.6, is attributed to the aryl sulfonic acid groups. The sulfonic acid contents, as determined by microanalysis, indicate that there is a drop in sulfonation level of approximately 1mmol g-' between the surface and the centre of the structure. Overall sulfonic acid content is somewhat lower than was obtained in the small scale experiment, but still respectable at an average of 2.4 mmol g-' (ca. 42% conversion).The sulfonation profile is shown in Fig. 2. The difference in extent of sulfonation between interior and exterior is simply due to diffusion of the reagent solution across a relatively large distance (radius of sample is 23 mm). As the reaction proceeds, the concentration of reagent in solution is depleted throughout the sample. However, unchanged lauroyl sulfate in the bulk solution can diffuse quickly to polymer chains closer to the monolith surface, hence maintaining the local reagent concentration, whereas polymer near the centre of the monolith would be expected to experience a more serious depletion in reagent levels. This is likely to lead ,,,,,g2 0.0 l 0 5 10 15 20 25 distance from centrdmm Fig. 2 Sulfonation profile of monolithic poly(styrene-DVB) PolyHIPE@ with lauroyl sulfate (55 "C, 48 h) ultimately to different reaction rates throughout the polymer monolith, since the reaction kinetics are dependent on c~ncentration.'~ Another factor which may affect the uniformity of sulfon- ation is the viscosity of the reagent solution, which was quite high.This would increase the time taken for equilibration of the solution throughout the entire sample and would also hinder transport of reagent molecules from the external solu- tion to reactive sites in the interior of the polymer monolith. Nitration Polystyrene can be nitrated using a mixture of concentrated nitric and sulfuric acids;15 however, degradation of the polymer can occur. Several milder reagents for general aromatic nitration have been developed, including acetyl nitrate in CC14,15316which gave low degrees of substitution with poly- styrene.Aromatic nitration can also be performed with N-nitropyrazole, in the presence of an acid ~atalyst,'~with N-nitropyridinium salts" and with nitric acid in the presence of either trifluoromethanesulfonic acid" or anhydride.20 Several inorganic reagents have also been used, such as ceric ammonium nitrate2' and the system NaN0,-C1SiMe3-AlC1, .22 However, these methods involve either heterogeneous con-ditions or polar solvents, making them unsuitable for PO~YHIPE@nitration. Crivel10~~has described a method for mild, efficient nitration of various aromatics, including polystyrene, with ammonium nitrate and trifluoroacetic anhydride (TFAA).Hodge et ~1.~~ have successfully used this system to nitrate polyacenaphthy- lene to high degrees of substitution. A more hydrophobic reagent was prepared with te trabu tylammonium nitrate (TBAN) and TFAA, which was used to nitrate aromatic compounds in chlorinated solvents at ambient tempera-ture~~'~~~(Scheme 2). Crosslinked polystyrene PolyHIPE@ materials were initially nitrated with a 1 :2 mixture of concentrated nitric and sulfuric acids at room temperature. On a small scale, this proved quite successful, with a high level of nitration being achieved; 8.6 mmol g -'represents essentially complete monosubstitution of aromatic rings. Peaks at 1534 cm-' (NO2 asymmetric stretch) and 1355 cm-I (NO2 symmetric stretch) in the FTIR spectrum of the product confirmed that aromatic nitration has occurred.HNO,-&S 0, ;8 -2\\ Bu,"O,-(CF,CO),O Scheme 2 Nitration of poly(styrene-DVB) PolyHIPE@ J. Muter. Chem., 1996, 6(5), 719-726 723 The reaction was repeated, with the polymer preswollen in DMF and subsequent addition of the acid mixture However, it can be seen from the microanalytical data that this procedure does not lead to a high degree of substitution The reaction is extremely non-uniform In the some areas, the PolyHIPE'@ cubes are highly coloured, whereas others are completely white It is evident that the nitrating reagents did not mix sufficiently with DMF in the interior of the polymer matrix The progress of the nitration reaction involving nitric and sulfuric acid was followed by removing a small cube of PolyHIPE@ from the reaction flask, at various time intervals, quenching in dilute aqueous sodium hydroxide and determin- ing the nitrogen content of the polymer by microanalysis of the crushed PolyHIPE@ cube The concentration of nitro groups with time is plotted in Fig 3 Almost complete monosubstitution is achieved after 4 h, and the subsequent increase in NOz content is only slight However, since a significant extent of reaction occurs after only 1h at slightly below room temperature, this method of nitration may not be suitable for the uniform chemical modification of large, monolithic samples Nevertheless, nitration of a PolyHIPE@ macrosample was attempted with the above reagent system A monolith was vacuum-filled with a 2 1 mixture of sulfuric and nitric acids, pre-cooled to ice temperature After washing and drying the product the nitro-group content along the radius of the cylindrical sample was determined from the nitrogen microana- lytical data The results are plotted in Fig 4 Degrees of nitration are evidently very low in the interior of the porous polymeric matnx, this was also apparent from the white colour in the core of the sample Obviously, the hydro- philic acid mixture is incapable of fully penetrating the pore structure of the hydrophobic polymer, leading to low levels of substitution towards the centre The highly nitrated surface sample possessed an identical FTIR spectrum to the PolyHIPE@ product previously nitrated with nitric and sulf- uric acids A more hydrophobic nitrating system was required The combination of ammonium nitrate and trifluoroacetic anhy- dnde, which is homogeneous in chlorinated solvents, was 1 I 1 I I 5 10 15 20 25 bh Fig.3 Progress of poly(styrene-DVB) PolyHIPE@ nitration with H,SO,-HNO, (3 1, room temp ) I 1 I I J 5 10 15 20 25 distance from centre/mm Fig. 4 Nitration profile of monolithic poly (styrene-DVB) PolyHIPE@ with H,SO,-HNO, (2 1, room temp, 24 h) 724 J Muter Chem , 1996,6(5), 719-726 employed It was envisaged that this would lead to a more uniform modification of PolyHIPE@ monoliths On a small scale, however, a relatively low degree of modification is obtained, 2 1 mmol g-' is equivalent to only 25% conversion Exchanging the salt for the more hydrophobic tetrabutylammonium nitrate results in a two-fold increase in the degree of substitution (42 mmol g-l, 50% substitution), on a small scale, which was deemed satisfactory for the monolith modification The polymeric products from both reactions have identical FTIR spectra to the previous nitrated PolyHIPE@ samples In addition, a sharp signal at 6 146 8 in the solid state I3C NMR spectrum of the latter product indicates that aromatic nitration has occurred The active species in these reactions is thought to be trifluoroacetyl nitrate, which forms from the nitrate salt and trifluoroacetic anhydride (Scheme 3) 23 Trifluoroacetyl nitrate can dissociate into its component ions, however, it is not known whether reactions involve intact tnfluoroacetyl nitrate, associated ions or free ions as the electrophilic species (Scheme 4) 26 In non-polar solvents such as those employed in the present study, it is probable that both undissociated trifluoroacetyl nitrate and tightly bound ions are the nitrating species The tetrabutylammonium nitrate-trifluoroacetic anhydnde (TBAN-TFAA) system was used to nitrate a monolithic sample of poly(styrene-DVB) PolyHIPE@, producing a material with the same FTIR spectrum as before The nitration profile results are shown in Fig 5 These indicate that a much lower overall degree of substitution was achieved compared with the small scale experiment However, the difference in NO2group content between surface and interior is not so great and is certainly an improvement relative to the sample nitrated with the acid mixture It is thought that the relatively low extent of nitration is due to incompatibility between the nitrate salt and the non- polar polymer matrix This problem may be accentuated with large PolyHIPE@ samples since the diffusion distance is increased Also, it was evident that the nitrated polymer did not swell in DCM Therefore, after a certain degree of substi- tution, the remaining reactive sites of the polymer might not 0 0 I/ //(CF&O),O + M+N03-====== CF3C\ + CF&\ ON02 0-M+ M = NH4+,NBu: Scheme 3 0 -CF,< -CF3CO;NOg CF3COz-+ NO2+ ON02 I / Scheme 4 4q,l,c O OO 5 10 15 20 25 distance from centre/mm Fig.5 Nitration profile of monolithic poly(styrene-DVB) PolyHIPE@ wlth TBAN-TFAA (30 "C,24 h) be as accessible to the reagents as at the start of the reaction. However, the overall ability of DCM to swell the starting material produces a more uniformly nitrated porous material. Bromination Bromination of polystyrene resins is carried out with bromine C-Br range (6 20-30) indicates that neither heterolytic bro- mination nor addition across residual double bonds in the starting polymer has occurred to any appreciable extent. This system therefore appeared to be an ideal one with which to achieve uniform chemical modification of a PolyHIPE* macrosample.Treatment of a cylinder of poly (styrene-DVB) PolyHIPE@ under similar conditions did and a Lewis acid catalyst, such as FeC1, or T~(OAC)~.~~indeed lead to bromination of the material to an almostHowever, with the former catalyst the level of bromination is completely homogeneous extent (Fig. 6). The results indicate difficult to control and reproduce. The latter is costly and that the concentration of bromine in the centre of the sample requires an excess to achieve high degrees of substitution. is 3.6 mmol g-l, whereas at the surface it is 3.7 mmol g-'. Another aromatic bromination method involves the use of bromine with pyridine.,' The bromine adds to the pyridine, forming the N-bromopyridinium bromide salt (3).The electro- philic activity of bromine is increased in this way.Additionally, Camps et have used stannic chloride as the Lewis acid catalyst in the bromination of polystyrene with bromine. The reaction is homogeneous in CH,Cl,, and is performed at room temperature. Bromination of poly (styrene-DVB) PolyHIPE@ was carried out with these latter two systems (Scheme 5). Reaction with bromine and pyridine in chloroform on a small scale caused the rapid precipitation of what was pre- sumed to be N-bromopyridinium bromide salt. Despite this, refluxing the heterogeneous mixture for 24 h gave a reasonable level of bromination. The salt may have a limited solubility in CHC1, at higher than ambient temperatures, which allows the transport of small quantities to the reactive sites of the polymer.Pyridine is regenerated upon reaction with polymer aromatic groups, and this can reform the catalyst salt in close proximity to the polymer internal surface. Thus, a relatively high concen- tration of brominating reagent may be present in the interior of the polymer matrix. This experiment was repeated with chlorobenzene, in which it was found that no precipitate had formed when bromine and pyridine were added in a previous solubility test. In addition, this chlorinated aromatic solvent causes extensive swelling of the polymer. The reaction mixture was indeed homogeneous initially, however, a red precipitate formed after about 1 h. Nevertheless, the flask was heated at 120°C for 24 h, affording a polymer product containing 3.0 mmol g-' of bromine.Rather curiously, the mass of the product was slightly lower than that of the starting material, implying that some polymer degradation had occurred. Perhaps the high tempera- ture, in the presence of bromine and air, is the cause of this. Despite achieving reasonable levels of bromination with pyridine and bromine, it was believed that improvements could be made in a completely homogeneous system, preferably with a swelling solvent. Therefore, the combination of bromine with the Lewis acid catalyst stannic chloride was investigated. On a small scale, after 24 h at 35 "C under nitrogen, a polymer material containing 4.3 mmol g-' of bromine was obtained. Aromatic bromination was confirmed by the appearance of a signal at 6 120.2 in the 13C solid state NMR spectrum of the product.Furthermore, the absence of peaks in the aliphatic Br Scheme 5 Bromination of poly (styrene-DVB) PolyHIPE@ The constant degree of substitution throughout the monolith can be attributed to a combination of factors such as a homogeneous reaction mixture, a good swelling solvent for the polymer, high compatibility between polymer and reagents and the ability of the solvent to swell the product. This last property is important if a high level of substitution is to be achieved as it allows continued access of the polymer active sites to the reagent species. The preparation of uniformly sulfonated, nitrated and brominated monolithic PolyHIPE@ materials is an import- ant advance in PolyHIPE@ chemistry.Sulfonated poly-(styrene-DVB) PolyHIPE@ polymers may find applications as strong acid catalysts, which are important in a number of industrial processes, or as the basis of highly porous ion exchangers. Nitrated PolyHIPE@ could be reduced to the amino-functionalised species, which would provide a route to further chemical modification via diazotisation of the amino group. Finally, the brominated polymer could be lithiated by lithium-bromide exchange,22 allowing further specific electro- philic addition reactions to be carried out. The materials described in this publication now offer access to a wide variety of novel, functionalised, highly porous monolithic polymers. Conclusions The chemical modification of poly (styrene-DVB) PolyHIPE@ materials was carried out with the aim of producing uniformly functionalised monolithic samples.Thus, the sulfonation, nitration and bromination of cylinders of poly(styrene-DVB) PolyHIPE@ was investigated employing mild, organic-soluble reagents. Sulfonation with lauroyl sulfate in cyclohexane affords reasonably uniform modification to an average level of 2.4 mmol g- '. Nitration was performed with the tetrabutyl- ammonium nitrate-trifluoroacetic anhydride system in DCM at room temperature, which gives a product possessing a moderate level of nitration (1.8 mmol g-' average) with a slight drop between centre and surface. Bromination was conveniently carried out with bromine and the Lewis acid catalyst SnC14, again in DCM at room temperature.This results in completely uniform substitution, to a degree of 3.7 mmol g- '. The products have additionally been character- ised by I3C solid state NMR spectroscopy. From the studies, a number of conclusions have been made regarding the requirements to achieve a high and uniform *--0 -3.0 3--2.0 8-E 1.0 -.-5 I-c 1 I I I I0.0; 5 10 15 20 25 distance from centrdmm Fig. 6 Bromination profile of monolithic poly(styrene-DVB) PoIyHIPE@ with Br,-SnC1, (35 "C, 24 h) J. Muter. Chem., 1996, 6(5),719-726 725 degree of substitution These include a good swelling solvent for the starting polymer, homogeneous reaction conditions, swellability of the product in the solvent and high compatibility between reagents and polymer Continued and easy access of the polymer reactive sites should be assured under these 11 12 13 14 H R W Ansrink and H Cerfontain, Recl Trav Chim Pays-Bas, 1992,111,183 R A Weiss, A Sen, C L Willis and L A Pottick, Polymer, 1991, 32,1867 Z Su, X Li and S L Hsu, Macromolecules, 1994,27,287 W A Thaler, Macromolecules, 1983, 16, 623 conditions 15 A Philippides, P M Budd, C Price and A V Cuncliffe, Polymer, 1993,34,3509 16 E S Rudakov, V L Lobachev and 0 B Savsunenko, Kinet N R C is grateful to the EPSRC for the provision of a CASE studentship and to Unilever Research, Port Sunlight, the Cooperating Body The authors would also like to thank Dr Robert Sowden of The British Council in Tokyo for funding the visit of N R C to Tokyo Institute of Technology 17 18 19 Catal, 1990,31,938 G A Olah, S C Narang and A P Fung, J Org Chem, 1981, 46,2706 E K Kim, K Y Lee and J K Kochi, J Am Chem SOC, 1992, 114,1756 C L Coon, W G Blucher and M E Hill, J Org Chem, 1973, 38,4243 20 G A Olah, V P Reddy and G K S Prakash, Synthesis, 1992, References 21 1087 S DinGturk and J H Ridd, J Chem SOC, Perkin Trans 2, 1982, 1 2 3 4 5 6 7 8 9 D Barby and Z Haq, Eur Pat 0060 138 (to Unilever), 1982 N R Cameron and D C Shernngton, Adv Polym Sci, 1995, in the press J M Williams and D A Wrobleski, Langmuir, 1988,4,656 J M Williams, A J Gray and M H Wilkerson, Langmuir, 1990, 6,437 P Hainey, I M Huxham, B Rowatt, D C Sherrington and L Tetley, Macromolecules, 1991,24, 117 P Hodge, in Syntheses and Separations Using Functional Polymers, ed D C Sherrington and P Hodge, Wiley, UK, 1988 P Hainey, BSc Thesis, 1988, University of Strathclyde J R Millar, D G Smith, W E Marr and T R E Kressman, J Chem SOC,1963,218 B Chakravorty, R N Mukherjee and S Basu, J Membr Sci, 1989,41,155 22 23 24 25 26 27 28 29 30 31 965 G A Olah, P Ramaiah, G Sandford, A Orlinkov and G K S Prakash, Synthesis, 1994,468 J V Crivello, J Org Chem, 1981,46,3056 P Hodge, B J Hunt and I H Shakhshier, Polymer, 1985,26,1701 B Masci, J Org Chem, 1985,50,4081 B Masci, Tetrahedron, 1989,45,2719 M J Farrall and J M J Frechet, J Org Chem, 1976,41,3877 B S Furniss, A J Hannaford, P W G Smith and A R Tatchell, Vogels Textbook of Practical Organic Chemistry, Longman, Harlow, UK, 5th edn 1989, p 860 M Camps, J P Montheard, F Benrokia, J M Camps and Q T Pham, Eur Polym J, 1990,26,53 M Camps, J P Montheard and F Benrokia, Eur Polym J, 1991, 27,389 M Camps and F Benrokia, Polym Commun ,1991,32,433 10 A G Theodoropoulos, V T Tsakalos and G N Valkanas, Polymer, 1993,34, 3905 Paper 5/06569K, Received 15th October, 1995 726 J Muter Chem, 1996, 6(5),719-726

ISSN:0959-9428    

DOI:10.1039/JM9960600719

出版商:RSC    

年代:1996

数据来源: RSC