Self-assembled monolayers of phthalocyanine derivatives on glass and silicon Michael J. Cook,* Roxana Hersans, Jim McMurdo and David A. Russell School of Chemical Sciences, University of East Anglia, Norwich, UK NR4 7TJ The synthesis of three phthalocyanine derivatives functionalised with seven or eight substituents including either one or two trichlorosilylalkyl chains is described. Self-assembled monolayers of the derivatives covalently bound to silicon and glass have been formed and characterised by FTIR and visible region spectroscopies. The fabrication of thin films of phthalocyanine derivatives by oxyphthalonitriles 4 and 5 respectively. Phthalonitrile 4 was deposition from the vapour phase, by spin coating, and by prepared by acid-catalysed deprotection of 4,5-dicyanoisoprop- transfer of monolayers via the Langmuir-Blodgett method is well established1Y2 and provides formulations of potential value in displays, chemical sensors, and photoconducting devices.A difficulty with films deposited from the vapour phase and by spin coating is that there is often rather limited control over film thickness and crystallite size. The Langmuir-Blodgett technique, on the other hand, can produce films of precise thickness, with some degree of three dimensional ~rder.~.~ However, the films are often fragile; for device applications more robust and abrasion-resistant films are desirable. Techniques leading to self-assembled monolayer (SAM) films3 offer the prospect of obtaining ultrathin films chemically bound to the substrate surface.Such films are much more robust but compounds for this type of deposition require specific functionalisation. Recently, we described the formation of a phthalocyanine SAM film by depositing a disulfide derivative onto a gold surface.' In this paper, we report what we believe to be the first examples of phthalocyanine SAM films on glass and silicon. These have been obtained using three novel phthalocyanines bearing seven or eight substituents of which one or two are alkyl chains bearing a terminal trichlorosilyl group. The latter reacts with surface oxides and hydroxides to form films which have been characterised by both visible region and IR spectroscopy. Results and Discussion Phthalocyanine derivatives for SAM film formation Previous work from these laboratories has produced a number of isomerically pure octa-substituted phthalocyanine deriva- tives.6 Alkyl substituents confer a degree of solubility in organic solvents such as dichloromethane, toluene and tetrahydrofuran, a requirement for the SAM deposition method, as well as mesogenic behaviour,6-8 a potentially useful property that may encourage self organisation of the molecules during the mono- layer forming process.Accordingly, for the present work, attention was focussed on non-uniformly octa-substituted derivatives which contain a number of alkyl substituents and either one or two alkenyl chains. In principle, the latter can be hydrosilylated with trichlorosilane to give the desired derivatives for SAM deposition.A non-uniformly substituted compound described in recent work was the hydroxyalkyl phthalocyanine derivative la.9 In the present study, this compound was treated with methanesul- fonyl chloride and triethylamine in dichloromethane to give the methanesulfonate (mesylate) lb. The latter was treated with sodium but-3-en-1-olate in dry THF to give the monoalkenyl phthalocyanine lc. Two further alkenyl derivatives, 2a and 3a, were also synthesised. The immediate precursors to these were 3,6-di~ctylphthalonitrile~and the novel bis- and mono-butenyl- C0H17 N la X=H Ib X=SO&Ha IC X=(CH&CH=CH* Id X=(CH2)4SiCt3 2a X=(CH2),CH=CH2 2b X=(CH2),SiCJ3 -C0H17 3a X=(CH2)&H=CH2 3b X=(CH2)4SiC13 J.Mater. Chem., 1996, 6(2), 149-154 149 Scheme 1 Reagents: i, HCl,,-EtOH; ii, 4-bromobut-l-ene, K2C03, MEK Scheme 2 Reagents: i, but-3-en-1-01, K2C03, DMF ylidenecatechol" followed by base catalysed 0-alkylation with 4-bromobut-1-ene in methyl ethyl ketone (MEK), Scheme 1. Phthalonitrile 5 was prepared in one step from the commer- cially available 4-nitrophthalonitrile, Scheme 2. Base-catalysed crossed condensation of an excess of 3,6-dioctylphthalonitrile with 4 and with 5 afforded the required phthalocyanines 2a and 3a respectively. These were readily separated from the side-products of condensation, the main one being 1,4,8,11,15,18,22,25-octaoctylphthalocyanine,by routine chromatographic procedures. The three phthalocyanines lc, 2a and 3a were then converted into the corresponding trichlorosilylalkyl derivatives Id, 2b and 3b respectively.This was achieved by chloroplatinic acid- catalysed hydrosilylation of the terminal double bond with trichlorosilane in dry benzene or toluene under dry argon in a sealed tube at 100°C;ll there is no reason to suppose that side reactions occur involving the phthalocyanine nucleus because, under the same conditions, 1,4,8,11,15,18,22,25-octa-octylphthalocyanine was recovered intact. The required deriva- tives Id, 2b and 3b were recovered by evaporating the solution under argon and redissolving them in dry THF from which solutions they were deposited onto silicon or glass as described below. Characterisation of precursor phthalocyanines Compounds lb, lc, 2a and 3a each gave a satisfactory elemental analysis and a 'H NMR spectrum fully consistent with the structure of the compound.In particular lc, 2a and 3a each showed the signals characteristic of the protons for terminal alkene groups. They also showed aromatic proton signals expected for the ring substitution patterns of the compounds. For example, lc shows two well resolved AB patterns with signals at 6 7.64 and 7.73, and at 6 7.79 and 7.83. The remaining four protons are accidentally equivalent at 6 7.88. Compound 2a, the most symmetrical compound, shows a singlet at 6 8.19 for the protons at the C-1 and C-4 sites, a singlet at 6 7.96 assigned to the protons at the C-16 and C-17 positions and the remaining four protons give rise to an AB pattern, 6 7.52 and 7.63.The most complex set of aromatic proton signals arises from 3a. The spectrum shows the proton at C-4 to be the most deshielded, 6 8.8. The proton at C-1 appears at 6 8.39 and that at C-3 at 6 7.45. All show the appropriate splitting patterns. There are also two further AB patterns in the region 6 7.65-7.85 and a singlet for the remaining two protons at 6 7.93. Thermotropic mesophase behaviour among 1,4,8,11,15,18,22,25-octasubstitutedphthalocyanines is now well documented7.* and the four new compounds all proved to be enantiotropic liquid crystals, i.e. they exhibited one or more mesophases during both heating from the crystal state and on cooling from the isotropic liquid, I.Transition tempera- tures were monitored by polarised light microscopy and are collected in Table 1. The mesophases were identified by comparing their birefringence textures with those for other compounds whose mesophases have been characterised fully by X-ray diffraction methods.8 On cooling from the isotropic liquid all four compounds exhibited a mesophase, denoted as D,, which has a characteristic fan type texture. This type of birefringence is observed for discotic columnar mesophases of two dimensional hexagonal symmetry with disordering within the stacks, Dhd.Compounds lb, lc and 2a, on further cooling, exhibited a second mesophase, D2, having a needle texture. This is characteristic of the second, lower temperature, Dhd mesophase exhibited by some octaalkyl derivatives.' On further cooling, compounds lb and 2a crystallised but compound lc did not solidify even when cooled to -50°C.On cooling compound 3a from the D, mesophase, a mosaic texture of a further mesophase, D3, was observed. This texture is characteristic of a disordered discotic columnar mesophase of rectangular symmetry, Drd.' On further cooling, this gave way to the needle texture of the D, mesophase prior to crystallisation. SAM film preparation Silicon wafers and glass slides used as substrates were cleaned and rendered hydrophilic immediately prior to use, then rinsed with Millipore@ water, acetone, dry THF and dried in a stream of dry nitrogen, see Experimental section. The use of freshly cleaned wafers and slides proved to be essential for satisfactory film deposition; extended rinsing of the substrates in Millipore@' water for 30min proved to be detrimental to the subsequent film deposition process, giving inferior quality films.Attachment of the phthalocyanines Id, 2b and 3b to the wafer or slide surface was achieved simply by immersing the substrate in a ca. 3 x lop3mol dmp3 solution of the phthalocy- anine in THF for 24 h under an argon atmosphere. Extending the time to 72 h gave films showing the same spectral properties on subsequent analysis, see below. On withdrawal from the solution, the SAM coated substrates were washed immediately in fresh THF; failure to wash the substrate immediately on removal gave uneven films.We propose these arose from evaporation of the small amount of retained solution leaving behind non-covalently bound phthalocyanine material. This, in the presence of atmospheric moisture, could well form oligomers which would be difficult to remove. Spectroscopic characterisation of films Evidence for SAM film deposition onto silicon was obtained from transmission FTIR spectroscopy. The FTIR spectra for the SAM films obtained from all three compounds showed well defined bands in the C-H stretching region, with the spectrum of the film obtained using 3b, Fig. 1, giving rise to the highest intensity absorbance bands. The spectrum shows stretching modes at 2868 (CH2 symmetric stretch), 2933 (CH, asymmetric stretch, absorbance 0.02) and 2958 cm-' (CH, in- plane asymmetric stretch).Corresponding modes for the SAM Table 1 Compounds lb, lc, 2a and 3a, transition temperatures ("C) observed during heating (first set of data) and cooling" lb 51.5; 48.5 68.5; 67.5 170.6; 169.3 lb 66.0; 56.4 166.7; 164.0 2a 153.0; 129.0 170.0; 170.0 248.0; 248.0 3a 80.0; 50.0 128.0; 128.0 163.0 163.0 250.0; 250.0 a D1,fan texture, D,, needle texture, and D3,mosaic texture, are tentatively assigned as Dhd, Dhd, and D,, mesophases respectively, see text. 150 J. Mater. Chem., 1996, 6(2), 149-154 0 3200 3000 2800 2600 wavenum ber/cm-' Fig. 1 Part of the FTIR transmission spectrum of the SAM film obtained from 3b deposited onto the two sides of a silicon wafer.The spectrum shows the aliphatic C-H stretching modes. film from 2b appeared at 2870, 2928 (absorbance 0.005) and 2955 cm-'. The absorbance values were typically >50% more intense for films obtained from 3b over those from 2b which contains four more CH2 groups. The corresponding spectrum for the SAM film formed from Id gave bands at 2865, 2925 (absorbance 0.002) and 2960 cm-'. The absorbances in the films from Id were all lower than for the other films despite the marginally larger number of methylene groups. The absorp- tion intensities are not necessarily a linear measure of the number of CH2 groups present because the groups may well be anisotropically ordered within the film; the electric field component of the incident radiation interacts only with the component of the dynamic dipole moment of the C-H vibration which is parallel with the substrate surface.Visible region spectra were recorded of the SAM films deposited onto glass and each showed a Q-band broadened relative to that observed for the solution phase. For each phthalocyanine, the SAM film spectrum was reproducible from film to film and over different regions within the same film. The SAM derived from 3b shows the highest intensity Q-band absorbance, Fig. 2; in reality, the spectrum corresponds to a double SAM film (one either side of the glass slide), indicating an absorbance of ca. 0.005 per monolayer. The corresponding spectrum for the double SAM film derived from 2b, Fig. 3, I I I I 500 600 700 800 900 wavelengthhm Fig.2 The visible region spectrum of the SAM film derived from 3b deposited onto the two sides of a glass slide I I I I 500 600 700 800 900 wavelengthhm Fig.3 The visible region spectrum of the SAM film derived from 2b deposited onto the two sides of a glass slide shows an absorbance of ca.0.003 per monolayer. Both absorp- tion envelopes appear to show some degree of structure, particularly that in Fig. 3. In contrast the film derived from Id shows a low intensity absorption (absorbance ca. 0.001 per monolayer) and little structure. The band envelopes for the SAMs are different from those observed previously for LB12 and spin coated films13 of octa- alkylated phthalocyanines. Those bearing octyl chains show, relative to their solution phase spectra, a characteristic red and blue shifted band.This is illustrated in Fig. 4 where spectrum (a) is that for a spin coated film of compound 2a. Recent work has shown that mesogenic phthalocyanines for- mulated as spin coated films exhibit the same thermotropic liquid crystal behaviour as the bulk material^.'^ Spectra (b) and (c) in Fig. 4 show the spin coated film of 2a at temperatures corresponding to the D,, mesophase and the isotropic liquid, respectively. The absorption envelopes of the SAM films are most similar to spectra (b)and (c) indicating that the molecular packing within the SAM films may be comparable to the looser packing of either the liquid crystal phase or the liquid phase.The absorbance from the films decreases in the same order as for the FTIR bands observed for the corresponding films I I I I 1 500 600 700 800 900 wavelengthhm Fig. 4 The visible region spectra of a spin coated film of 2a. Spectrum (a), at room temperature and showing a broad band exciton split absorbance. Spectrum (b), at 200 "C corresponding to the Dhd mesophase and spectrum (c) at 260°C at which temperature the film has melted. J. Muter. Chem., 1996, 6(2), 149-154 151 on silicon. However, as with the FTIR results, it is difficult to use the absorption intensities to quantify the amount of material bonded to the substrate. Absorption coefficients, E, of metal-free phthalocyanines are normally quoted for conditions where aggregation is minimal and are of the order of 1.5 x lo5dm3 mol-l cm-l.For example, absorption coefficients for the precursor phthalocyanines, 2a and 3a, as dilute solutions in cyclohexane are 1.42 x lo5 (at 4.4 x mol dm-3) and 1.48 x lo5 (at 4.4 x mol drn-,), respect-ively. The crystal state molality of octa-substituted derivatives structurally related to the present compounds is ca. 0.94.105 These data predict a solid state absorbance of ca. 0.0014 per A of film thickness but clearly refer to a close packed film structure in which there are no exciton coupling interactions of the transition dipoles. It also refers to a film containing random organisation of the molecules, as in the solution phase, whereas in practice the molecules may be packed aniso-tropically.The two n-n* transitions contributing to the Q-band absorption are polarized orthogonally in the plane of the ring16 and therefore, quite apart from film thickness and packing density, the absorbance is dependent upon the mean orientation of the rings relative to the incident light beam. The absorbance arising when the rings are aligned with their planes perpendicular to the direction of the interrogating beam is twice that when they are aligned parallel. Nevertheless, despite these qualifications, the absorbance data do suggest that Id has deposited to give incomplete surface coverage. On the other hand, the absorbances from the films derived from 2a and 3a are essentially consistent with a monolayer film, e.g.one in which the rings are lying parallel to the substrate surface. While a number of other film structures cannot be precluded, it is interesting to note that this type of surface coverage was deduced from a combined reflection-absorption infrared spectroscopy (RAIRS) and transmission FTIR study of a SAM film of a sulfanylalkylphthalocyanine on gold.17 Finally, a film derived from 3b on glass was heated to 255 "C and then cooled to room temperature. The visible region spectrum of the heat treated film gave the same Q-band structure and absorbance intensity to within ca. 5% of that of the original film, clearly demonstrating the thermal stability of the SAM film. Conclusions The three examples of trichlorosilylalkylated phthalocyanines investigated in the present study, suitably substituted to render them soluble in toluene and benzene, react at the surface of hydrophilic silicon and glass to form SAM films.The films can be detected spectroscopically. Films on silicon examined by transmission FTIR spectroscopy show C-H stretching modes and films on glass show absorbance in the visible region spectrum. The intensities of the absorption bands for films from the three derivatives differ. These differences are reproduc- ible and may indicate that satisfactory SAM formation is dependent upon the substituents on the phthalocyanine ring. The highest visible region absorption intensity, cu. 0.005 per monolayer was obtained for the film derived from 3b. The thermal stability of this film was demonstrated by heating it to 255°C and cooling to room temperature after which the visible region absorption band was essentially unchanged.Experimental Equipment and measurements FTIR spectra were recorded on a €310-RAD FTS 165 spectro- photometer. 'H NMR spectra were measured at 60 MHz using a JEOL JNM-PMX 60 spectrometer and at 270 MHz using a JEOL EX 270 spectrometer. Routine mass spectra were recorded using a Kratos MS 25 mass spectrometer. UV-VIS spectra were recorded using a Hitachi U-3000 spectrophoto- meter. Visible region spectra of spin coated films of 2a on glass slides were recorded at various temperatures using a Mettler FP82 Hotstage adapted to fit inside the sample compartment. Melting points were measured and thermotropic mesophase behaviour monitored using an Olympus BH-2 polarising microscope in conjunction with a Linkam TMS 92 thermal analyser and a Linkam THM 600 cell.Materials Silica gel (Merck 7734) was used in chromatographic separa- tions. TLC was performed using silica gel (Merck 5554) supported on aluminium sheets. Solvents were dried, where appropriate, over sodium and distilled under an atmosphere of dry nitrogen. Phthalonitrile precursors 4,5-Dicyanoisopropylidenecatechol,mp 198-199 "C (lit.," 193°C) was prepared from catechol according to the route outlined in ref. 10. 3,6-Dioctylphthalonitrile was prepared from thiophene according to the route outlined in ref. 7. 4,5-Dihydroxyphthalonitrile. 4,5-Dicyanoisopropylidene-catechol (5.0g, 25mmol), 5 mol dmP3 hydrochloric acid (25 cm3) and ethanol (25 cm3) were heated under reflux with stirring for 3 h.The solvent was removed by distillation and the yellow residue recrystallised from water to give 4,5- dihydroxyphthalonitrile (4.0 g, 100%) as colourless needles, mp 285 "C, dH(60 MHz; [2H,]acetone) 7.40 (2 H, s). This was used as described below without further purification. 4,5-Bis(but-3-eny1oxy)phthalonitrile (4). 4,5-Dihydroxy-phthalonitrile (1.0g, 6.25 mmol) and potassium carbonate (5 equiv.) were stirred in MEK (100 cm3) for 10 min, after which 4-bromobut-1-ene (2.2 g, 16 mmol) was added. This mixture was stirred under reflux for 72 h after which time TLC analysis indicated that the reaction was part complete. A few drops of dicyclohexane-18-crown-6 were added and heating under reflux continued for 48 h after which time TLC analysis indicated that there was no remaining starting material.The reaction mixture was filtered and the solvent removed under reduced pressure to give ca. 2 g of a crude solid. Column chromatography (silica gel, eluent dichloromethane) followed by recrystallisation from light petroleum (bp, 100-120 "C)gave 4,5-bis(but-3-enyloxy)phthalonitrile ( 1.01 g, 60%) as colourless needles, mp 126 "c(Found: c, 71.4; H, 5.9; N, 10.4. C16H,6N,02 requires C, 71.6; H, 6.0; N, 10.4%); vrnax/cm-l 2225 (CN); dH(60 MHz; CDCl,) 2.7 (4 H, q), 4.2 (4 H, t), 5.2 (4 H, m), 6.0 (2 H, m), 7.2 (2 H, s); m/z 268. 4-( But-3-enyloxy)phthalonitrile (5). 4-Nitrophthalonitrile (2.0 g, 11.5 mmol) and but-3-en-1-01 (0.86 g, 12 mmol) in dimethylformamide (30 cm3) were heated, with stirring, to 100 "C.Freshly ground potassium carbonate (4.1 g, 30 mmol) was added in portions over 5 h and heating continued for a further 12h. The reaction mixture was allowed to cool to room temp., filtered and the filtrate washed with dichloro- methane (3 x 50 cm3). The combined organic extracts were washed with water (2 x 50 cm3), saturated brine (50 cm3), dried (MgSO,), filtered and the solvent removed under reduced pressure to give a pale yellow solid. The solid residue was dissolved in acetone and adsorbed onto silica gel (10g), loaded onto a silica gel column and eluted with light petroleum (bp 40-60 "C)-dichloromethane (1 :1).The pale yellow solid was chromatographed again (silica gel, carbon tetrachloride-dichloromethane, 2 :1 eluent) to afford 4-(but-3-enyloxy)ph- thalonitrile as a colourless solid (530 mg, 23%) mp 46-48 "C (Found: C, 72.5; H, 5.0; N, 14.1. Cl,Hl,N,O requires C, 72.7; H, 5.1; N, 14.1%); vrn,x/cm-l 2225 (CN); &(60 MHz; CDCl,) 152 J. Muter. Chem., 1996, 6(2), 149-154 2.7 (2 H, m), 4.4 (2 H, t), 5.2 (2 H, m), 6.0 (1 H, m) 7.8 (3 H, m); m/z 198. Phthaloc yanines 4-(5-Hydroxypentyl)-l-methyl-8,11,15,18,22,25-hexaoctyl-phthalocyanine, la, was prepared according to the route described in ref. 9. 1-Methyl-4-(5-rnethylsulfonyloxypentyl)-8,11,15,18,22,25-hexaoctylpht haloc yanine (1 b). The 5-hy drox ypen t ylp h thalocy- anine, la, from above (126 mg, 98 mmol) was dissolved in dichloromethane (10 cm3) and a large excess of triethylamine and methanesulfonyl chloride were added.The resultant mix- ture was heated under reflux for 2 h until TLC analysis indicated that the reaction had gone to completion. The solvent and excess reagents were removed under reduced pressure and the residue chromatographed (x 2) over silica gel [column one, eluent dichloromethane; column two, light petroleum (bp 40-60 "C)-dichloromethane, 2 : 11 to give 1-methyl-4-(5-methylsulfonyloxypentyl)-8,11,15,18,22,25-hexaoctylphthalocya-nine, lb (94.1 mg, 70%), mp 51.5 (K+Dhd), 68.5 (Dhd+Dhd), 170.5 "C (Dhd +I), (Found: C, 76.5; H, 9.4; N, 7.8. CgsH1,gNBOS requires C, 76.5; H, 9.4; N, 8.2); 6, (270 MHz; ['H6] benzene) -0.40 (2 H, s), 0.85 (18 H, m), 1.05-1.50 (64 H, m), 1.65-1.85 (8 H, m), 2.20 (2 H, q), 2.43 (6 H, m), 3.20 (2 H, t), 3.25 (2 H, t), 3.81 (3 H, s), 4.50 (2 H, t), 4.60-4.78 (12 H, m), 4.90-5.02 (2 H, m), 5.68-5.84 (1H, m), 7.64 (1H, d), 7.73 (1H, d), 7.79 (1H, d), 7.83 (1 H, d), 7.88 (4H, s).4-( 5-But -3-enyloxypenty1)- 1 -met hyl-8,1 1,15,18,22,25- hexa- octylphthalocyanine (lc). Sodium hydride (1 equiv.) was washed with dry light petroleum (bp 40-60°C) and then suspended in dry THF. The slurry was cooled to 10°C. But- 3-en-1-01 (1 equiv.) was added and the mixture allowed to warm to room temp. An excess of this mixture was added to 1-methyl-4-(5-methylsulfonyloxypentyl)-8,11,15,18,22,25-hexa-octylphthalocyanine, lb, (36.5 mg, 27 mmol) dissolved in dry THF.The solution was heated to reflux for 10 h when the reaction was complete as evidenced by TLC. The solvent was removed under reduced pressure and the residue chromato- graphed [silica gel, eluent light petroleum (bp 40-60 "C)-dichloromethane, 2 :11 to afford 4-( 5-but-3-enyloxy- pentyl )-l-methyl-8,11,15,18,22,25-hexaoctylphthalocyanine,lc (26.3 mg, 73%), mp 66.0 (Dhd+Dhd), 172 "c (Dhd+I), (Found: C, 80.2; H, 9.8; N, 8.1. C90H132N80 requires C, 80.55; H, 9.9; N, 8.35%); 6,(270 MHz; ['H6] benzene) -1.18 (2 H, s), 0.90 (18 H, m), 1.20-1.85 (64 H, m), 1.90-2.15 (6 H, m), 2.18 (3 H, s), 2.20-2.40 (8 H, m), 3.18 (3 H, s), 3.72 (2 H, t), 3.83 (2 H, t), 4.20 (4 H, t), 4.40 (4 H, t), 4.64 (4 H, t), 7.22 (1 H, d), 7.32 (1 H, d), 7.41 (1 H, d), 7.81 (4 H, dd).2,3-Bis( but-3-enyloxy)-8,11,15,18,22,25-hexaoctylphthalo-cyanine (2a). 4,5-Bis(but-3-eny1oxy)phthalonitrile (270 mg, 1 mmol) and 3,6-dioctylphthalonitrile (3.6 g, 9 mmol) in dry pentan-1-01 (30 cm3) were heated under reflux and lithium metal (0.4 g) was added in small pieces. Reflux was continued for 6 h and then the mixture was allowed to cool to room temp. Acetic acid (40 cm3) was added and the resultant slurry stirred for 1 h. The solvents were removed under reduced pressure and the residue triturated and washed with methanol to give a dark green solid which was dissolved into cyclo- hexane and then chromatographed over silica gel using first light petroleum (bp 40-60°C) as eluent to afford 1,4,8,11,15,18,22,25-octaoctylphthalocyanine,(1.30 g, 40%), identical by TLC to an authentic sample.The eluting solvent was then changed to light petroleum (bp 40-60 "C)-THF (9 :1) to give a second fraction that was further purified by column chromatography over silica gel (eluent cyclohexane-THF, 9 :1) to give a dark green solid that was recrystallised from THF- methanol to afford 2,3-bis(but-3-enyloxy)-8,11,15,18,22,25-hexaoctylphthalocyanine,2a (220 mg, 16%) as dark green crys- tals, mp 153 (K+Dhd), 170 (Dh,j-$Dhd), 248°C (Dhd+I) (Found: C, 79.6; H, 9.4; N, 8.6. CggH126N802 requires C, 79.6; H, 9.6; N, 8.4%); 6,( 270 MHz; C2H6] benzene) -2.00 (2 H, s), 0.90 (18 H, t), 1.40 (48 H, m), 1.90 (12 H, m), 2.23 (8 H, m), 2.43 (4 H, m), 2.90 (4 H, m), 3.92 (4 H, m), 4.32 (4 H, t), 4.40 (4 H, t), 4.62 (4 H, t), 5.40 (4 H, m), 5.25 (2 H, m), 7.52 (2 H, d), 7.63 (2 H, d), 7.96 (2 H, s), 8.19 (2 H, s); Ama,(4.4x lop6 mol dm-3 in cyclohexane)/nm 716.5 nm [&/dm3 mol-' cm-' 1.42x lo'], 679, 341.2-( But3-enyloxy)%, 11,15,18,22,25-hexaoctylphthalocyanine (3a). 4-(But-3-eny1oxy)phthalonitrile (200 mg, 1 mmol) and 3,6-dioctylphthalonitrile (3.6 g, 9 mmol) in dry pentan-1-01 (30 cm3) were heated under reflux. Lithium metal (0.4 g) was then added in small pieces and reflux continued for 6 h. The mixture was allowed to cool to room temp., acetic acid (40 cm3) was added and the resultant slurry stirred for 1 h. The solvents were removed under reduced pressure and the residue tritu- rated with methanol to give a dark green solid which was dissolved in cyclohexane and then chromatographed over silica gel using first light petroleum (bp 40-60 "C)as eluent to afford 1,4,8,11,15,18,22,25-octaoctylphthalocyanine,(1.31 g, 41 YO)and then light petroleum (bp 40-60 "C)-dichloromethane (3 :1) to give a second fraction.The latter was further purified by column chromatography over silica gel [eluent: light petroleum (bp 40-6OoC)-dichloromethane 3: 11 to give a dark green solid. Recrystallisation from THF-methanol followed by a further recrystallisation from THF-acetone afforded 2-(but-3- enyloxy)-8,11,15,18,22,25-hexaoctylphthalocyanine,3a (260 mg, 20%) as dark green Crystals mp 80 (K+Dhd), 128 (Dhd+Drd), 153 (Drd+Dlhd), 250°C (Dhd+I) (Found: c, 80.1; H, 9.5; N, 8.8.C84H120N80 requires c, 80.2; H, 9.6; N, 8.9%); 8H (270 MHz; ['H6] benzene) -1.40 (2 H, s), 0.90 (18 H, t), 1.40 (48 H, m), 1.90 (12 H, m), 2.30 (12 H, m), 2.70 (2 H, m), 4.20 (4 H, m), 4.60 (4 H, m), 4.70 (4 H, t), 5.30 (4 H, m), 6.20 (1 H, m), 7.45 (1 H, m), 7.65-7.85 (4H, m), 7.93 (2 H, s), 8.39 (1 H, d), 8.80 (1 H, d); Amax(4.4 x mol dm-3 in cyclohexane)/nm 718 (&/dm3 mol-' cm-l 1.48 x lo'), 680, 338. Hydrosilylation reactions. In a typical procedure, 4-( 5-but- 3-enyloxypenty1)-l-methy1-8,11,15,18,22,25-hexaoctylphthalo-cyanine, lc (25 mg), excess trichlorosilane, a catalytic amount of hexachloroplatinic acid (0.1 cm3, 0.1 mol dmp3 solution) and dry benzene or toluene were sealed in a glass tube under an argon atmosphere and then heated to 100°C for 48 h.Excess trichlorosilane and solvent were removed under reduced pressure and the residue dissolved in dry THF (4 cm3) and stored under a dry argon atmosphere. Depositionof self-assembled monolayer (SAM ) films Preparation of substrates. Silicon wafers and glass slides used as substrates were cleaned immediately prior to use in an ultrasonic bath using a mixture of 30% hydrogen peroxide in concentrated sulfuric acid, ('piranha' solution'') at 90 "C for 30 min or until they were judged to be completely hydrophilic. Substrates were then rinsed with Millipore@' water, acetone, dry THF and then dried in a stream of dry nitrogen. SAM deposition.In a typical procedure, a 3.2 x mol dm-3 solution of the trichlorosilylated phthalocyanine 3c (20 mg) dissolved in dry THF (4 cm3), prepared as above, was contained under an atmosphere of dry argon. The substrate was immersed in this solution for 24 h. Since the Si-C1 bond is susceptible to hydrolysis by atmospheric moisture each step was performed under a dry argon atmosphere. On withdrawal from the solution, the SAM film bearing substrate was washed immediately in fresh THF with sonication for 30 min. J. Muter. Chem., 1996, 6(2), 149-154 153 Spin coated films Spin coated films were prepared from solutions of 2a in THF (ca. 2.5 mg in 1.0 cm3) dropped onto a hydrophilic glass slide rotating at 2000 rpm using a Headway Spinner.Spinning was continued for 20 s by which time the solvent had evaporated. Comparisons of the visible region absorption intensities with those from LB films of known thicknesses prepared from comparably substituted phthalocyanines giving simil?r spectral features suggest that the film thickness was ca. 700 A.12 We thank the EPSRC (formerly SERC) and the EU HCM programme (grant no. CHRX CT94-0558) for financial sup- port. We also thank Mr. A. Jafari-Fini and Mr. T.R.E. Simpson for fruitful discussions. References A. W. Snow and W. R. Barger, in Phthalocyanines-Properties and Applications, eds. C. C. Leznoff and A. B. P. Lever, VCH, New York, 1989, p. 341. M. J. Cook in Spectroscopy of New Materials-Aduances in Spectroscopy Series, eds.R. J. H. Clark and R. E. Hester, Wiley, Chichester 1993 p. 87. A. Ulman, An Introduction to Ultrathin Films: from Langmuir- Blodgett to Self-Assembly, Academic Press, San Diego, London, 1991. M. J. Cook, Znt. J. Electron., 1994,76, 727. T. R. E. Simpson, D. A. Russell, I. Chambrier, M. J. Cook, A. B. Horn and S. C. Thorpe, Sens. Actuators, B: Chemical, 1995, 29, 353; I. Chambrier, M. J. Cook and D. A. Russell, Synthesis, 1995,1283. 6 M. J. Cook, J. Muter. Sci; Muter. Electron., 1994,5, 117. 7 I. Chambrier, M. J. Cook, S. J. Cracknell and J. McMurdo, J.Muter. Chem., 1993,3 841. 8 A. S. Cherodian, A. N. Davies, R. M. Richardson, M. J. Cook, N. B. McKeown, A. J. Thomson, J. Feijoo, G. Ungar and K. J. Harrison?Mol. Cryst. Liq. Cryst., 1991,196, 103. 9 G. C. Bryant, M. J. Cook, T. G. Ryan and A. J. Thorne, Tetrahedron, in the press. 10 I. Cho and Y. Lim, Chem. Lett., 1987,1,2107; I. Cho and Y. Lim, Mol. Cryst. Liq. Cryst. 1988,9, 154. 11 J. L. Speier, Advances in Organometallic Chemistry, Academic Press, New York, 1979, vol. 17, pp. 407-447. 12 M. J. Cook, J. McMurdo, D. A. Miles, R. H. Poynter, J. M. Simmons, S. D. Haslam, R. M. Richardson and K. Welford, J.Muter. Chem., 1994,4, 1205. 13 S. M. Critchley, M. R. Willis, M. J. Cook, J. McMurdo and Y. Maruyama, J. Muter. Chem., 1992,2, 157. 14 M. J. Cook, D. A. Mayes and R. H. Poynter, J. Muter. Chem., in the press. 15 I. Chambrier, M. J. Cook, M. Helliwell and A. K. Powell, J. Chem. SOC., Chem. Commun., 1992, 444 M. J. Cook, J. McMurdo and A. K. Powell, J. Chem. SOC.,Chem. Commun., 1993,903. 16 M. J. Stillman and T. Nyokong, in Phthalocyanines-Properties and Applications, eds. C. C. Leznoff and A. B. P. Lever, VCH, New York, 1989, p. 133. 17 D. A. Russell and T. R. E. Simpson, unpublished results. 18 A. H. Carim, M. M. Dovek, C. F. Quate, R. Sinclair and C. Vorst, Science, 1987,237,630. Paper 5105898H; Received 6th September 1995 154 J. Mater. Chem., 1996, 6(2), 149-154