J. CHEM. SOC. DALTON TRANS. 1991 2545Synthesis, Characterization, Luminescence Properties, andElectrochemical Behaviour of Ruthenium(ii) Complexes withTwo New Bi- and Tri-dentate 2-Pyridylquinoline LigandsSebastiano Campagna,a Antonino Mamo*nb and (the late) John K. Stille’a Dipartimento di Chimica lnorganica, Universita’ di Messina, V. Sperone 37, 98766 Vill. S. Agata(Messina), Italylstituto Chimico, Facolta di lngegneria, Universita fl di Catania, V. le A. Doria 8, 95 725 Catania, ItalyDepartment of Chemistry, Colorado State University, Fort Collins, CO 80523, USATwo new I igands, 4- phenyl-2 - (2’- pyridyl) qu i no1 i ne (ppq) and 2,6- bis (4’- phenyl - 2’-qu i nolyl) pyridi ne(bpqpy) and their ruthenium(ii) complexes [Ru(bipy),(ppq)] [PF,], (bipy = 2,2’-bipyridine) 1 and[Ru(bpqpy),] [PF,], 2 have been synthesized and characterized by conventional techniques.The IR,fast atom bombardment mass and UV-VIS spectra of the ligands and their complexes are brieflydiscussed. A study of the luminescence properties and electrochemical behaviour of the complexeshas shown that 1 is a good candidate as a luminescent and redox-active species to be incorporatedin a polymer polyquinoline-based backbone.The photophysics and photochemistry of [Ru(bipy),12 +(bipy = 2,2’-bipyridine) and of [Ru(terpy),12+ (terpy =2,2’ : 6’,2”-terpyridine) have been the subject of extensiveresearch. Rut henium(I1) polypyridine complexes have foundwidespread use as homogeneous catalysts for the photodecom-position of water,, as sensitizers for photoinduced electroninjection on semicond~ctors,~ in photoelectrochemical cells forthe production of dihydrogen,, and as sensitizers for thephotocleavage of DNA.’Lately many researchers have shown that it may be prefer-able to incorporate the ruthenium polypyridine complexes inpolymer matrices that may offer: (i) more rigidity of the system,slowing down radiationless-decay processes;’ (ii) the presenceof multiple binding sites that, when complexed, allow multi-electron transfer (a behaviour that can or could be essential forobtaining some valuable functions);’ ’r6,’ (iii) the opportunity ofa variety of chromophore-quencher combinations within thesame molecular framework.’Some of us have been interested in the synthesis of poly-quinolines,’ which are known for their thermal stabilities,chemical resistance and cross-linking ability.’ Since thepolyquinoline backbone possesses nitrogen atoms as potentialbinding sites for Ru”, we have designed copolymers containingin the main backbone, and not as a pendant group, bidentate(Scheme 1, a) and tridentate (Scheme 1, b) chelating units,which closely mimic the co-ordination of bipy and terpy at eachrut henium(I1) centre.This paper describes the synthesis and characterizationof two new ligands, 4-phenyl-2-(2’-pyridyl)quinoline (ppq)and 2,6-bis(4’-phenyl-2’-quinolyl)pyridine (bpqpy) (Scheme2), and of their ruthenium(I1) complexes [Ru(bipy),(ppq)]-[PFJ , 1 and [Ru(bpqpy),] [PF,] 2, respectively, alongwith their photochemical and electrochemical properties, asmodels for related polymeric polyquinoline ruthenium(I1) com-plexes.ExperimentalMaterials.-The complex [Ru( bipy) , C1 ,] -2H,O was pre-pared by the literature procedure.” All the reactions wereperformed under an inert atmosphere of nitrogen, and thesolvents were dried and stored under nitrogen and over 4Amolecular sieves.Melting points are uncorrected. Elementalanalyses were performed commercially. The compoundsRuC1,.3H2O and K,[RuCl,(H,O)] were purchased fromAldrich. All other reagents were reagent grade.Physical Measurements.-Proton NMR spectra were takenon a Bruker AC 250 instrument using SiMe, as internalreference, IR spectra (KBr disks) on a Perkin-Elmer 684spectrophotometer. Positive-ion fast atom bombardment(FAB) mass spectra were obtained on a Kratos MS 50 Sdouble-focusing mass spectrometer equipped with a standardFAB source, using 3-nitrobenzyl alcohol as a matrix.For the electrochemical measurements a three-electrode cellwas used, which was thermostatted at 25 “C by circulatingwater: working electrode, platinum microsphere; counterelectrode, platinum foil; pseudo-reference electrode, silver wirecalibrated internally through the ferrocene-ferrocenium couple;potential scan rate in differential pulse voltammetry (DPV)experiments, 5 mV s-’.Voltammetry studies were carried outusing a PAR 273 apparatus, driven by an IBM AT personalcomputer, through dedicated software. Acetonitrile was dis-tilled twice over CaH,; NBu,ClO, (Carlo Erba, polarographicgrade) was used without further purification.Dinitrogen,presaturated in MeCN, flowed into the cell during voltammetricexperiments.Ultraviolet-visible absorption spectra were recorded on aPerkin-Elmer 330 double-beam spectrophotometer using 1 cmquartz cells at room temperature, emission spectra with aPerkin-Elmer 650-40 spectrofluorimeter equipped with a red-sensitive Hamamatsu R928 phototube. Emission lifetimemeasurements were made with a JK System 2000 neodymiumYAG DPLY4 laser (Aex = 355 nm, pulse width 20 ns) and aTektronix 76 12 digitizer for data acquisition. Emissionquantum yields were measured by the optically dilute method,12the fluorimeter being calibrated with a standard lamp, and theemission spectra corrected for photomultiplier response.Theion [Ru(bipy),12+ in aqueous aerated solution was used asa quantum-yield standard, assuming a value of 0.028.13 Whennecessary, the solutions were deaerated with bubbling nitrogen2546 J. CHEM. SOC. DALTON TRANS. 1991Scheme I7 \ 6% / 4 'N, 5'6'PPq4WIPYScheme 2Preparations.-4-Phenyl-2-(2'-pyridyZ)quinoline. A mixtureof rn-cresol (40 cm3) and phosphorus pentaoxide (1.63 g) wasstirred at 150 "C for 2 h to afford a homogeneous solution. Aftercooling, 2-aminobenzophenone (4 g, 20.3 mmol) and 2-acetylpyridine (2.45 g, 20.3 mmol) were added with rn-cresol(l0cm3) to rinse the powder funnel. The reaction mixture washeated at 13&135 "C overnight. The dark solution was pouredinto ethanol (200 cm3) containing triethylamine (20 cm3).After30% of solvent was distilled off under reduced pressure, a white-yellow precipitate was collected by filtration, recrystallised fromethanol plus 10% triethylamine to give 4 g (70%) of ppq as off-white needles, m.p. 152-154 "C. 'H NMR [(CD,),CO]: 6 8.77(br, 1 H, J = 7.5, H3' of pyridine), 8.73 (br, 1 H, J = 4.9, H6' ofpyridine), 8.60 (s, 1 H, H3 of quinoline), 8.25 (br, 1 H, J = 8.5Hz, H8 of quinoline), and 8.1-7.6 (m, 10 H, aromatic andheteroaromatic H). Mass spectrum: rn/z 282 ( M ' + , 86%)(Found: C, 85.00; H, 5.05; N, 10.00. Calc. for CzoHI4N2: C,85.05; H, 5.00; N, 9.90(%,).2,6-Bis(4'-phenyf-2'-yuinofyL)pyridine. A mixture of rn-cregol(60 cm3) and phosphorus pentaoxide (2.62 g) was stirrer at150 "C for 2 h to afford a homogeneous solution.After cocling,2-aminobenzophenone (6.3 1 g, 32.0 mmol) and 2,6-diacetyl-pyridine (2.61 g, 16.0 mmol) were added, with rn-cresol(20 cm3)to rinse the powder funnel. The reaction mixture was heated at145 "C overnight. After cooling, the dark solution was pouredinto ethanol (350 cm3) containing triethylamine (35 cm3). Theyellow precipitate was collected by filtration and recrystallisedfrom toluene to give 6 g (78%) of bpqpy as white needles, m.p.277-279 "C. 'H NMR (C 0C13): 6 8.80 (d, 2 H, J = 7.9 Hz, H3,5of pyridine), 8.70 (s, 2 H, H3' of quinoline), and 8.3-7.5 (m, 19H, aromatic and heteroaromatic H). Mass spectrum: m/z 485(M'+, 40%) (Found: C, 86.30; H, 4.85; N, 8.70. Calc. forC,,H,,N,: C, 86.55; H, 4.75; N, 8.65%).[Ru(bipy),(ppq)][PF,],*H,O 1.To a refluxing solution of[Ru(bipy),C1J2H20 (0.156 g, 0.3 mmol) in ethanol (20 cm3)was added dropwise a solution of ppq (0.1 g, 0.35 mmol) inEtOH (20 cm3), and the mixture was allowed to reflux for 8 h.After concentration and addition of water (15 cm3) the mixturewas refluxed for 5 min and filtered while hot. The complex wasprecipitated as the hexafluorophosphate by dropwise additionof a 20% water solution of NH4PF6 (5 cm3)>. The red-orangeproduct was collected, washed with cold water and Et,O, andpurified by gel filtration on a column of Sephadex LH-20 inEtOH followed by recrystallisation from acetone-Et,O, to give0.22 g (72%) of 1 as red-orange crystals. 'H NMR [(CD3)ZCO]:6 9.18 (d, 1 H, H3' of pyridine, J = 8.14 Hz), 8.95 (m, 2 H, H3,3'of bipy), 8.78 (s, 1 H, H3 of quinoline), and 8.7-7.3 (m, 26 H,aromatic and heteroaromatic H) (Found: C, 47.75; H, 3.05; N,8.40.Calc. for C,,H3,Fl,N60P,Ru: C,47.85; H, 3.20; N, 8.35%).[Ru(bpqpy),][PF,],=H,o 2. To a blue hot (cu. 160 "C)solution of K,[RuCl,(H,O)] (0.15 g, 0.4 mmol) in glycerol (20cm3) was added dropwise a solution of bpqpy (0.431 g, 0.88mmol) in glycerol-EtOH (1 : 1 v/v, 60 cm3). After removal ofethanol, the mixture was stirred at 210 "C for 24 h, diluted withwater (80 cm3), refluxed again for 10 min and filtered while hot.The filtrate was heated to about 100°C and a hot aqueousammonium hexafluorophosphate solution (200/,, 10 cm3) wasadded. The dark purple powder formed was collected, washedwith cold water and Et,O, and purified by gel filtration on acolumn of Sephadex LH-20 in acetonitrile followed by re-crystallisation from acetonitrile-Et,O to give 0.312 g (57%) ofcomplex 2 as dark purple crystals.'H NMR (CD,CN): 6 9.20(d, 4 H, J = 7.9, H3,5 of pyridine), 8.81 (t, 2 H, J = 7.9 Hz, H4 ofpyridine), 8.36 (s, 4 H, H3' of quinoline), 7.8-7.3 (m, 32 H,aromatic and heteroaromatic H) and 6.69 (m, 4 H, H" ofquinoline) (Found: C, 60.70; H, 3.40; N, 6.35. Calc. forC3,H,,Fl,N,0P,Ru: C, 60.90; H, 3.50; N, 6.10%).Results and DiscussionSynthesis.-The Friedlander reaction has been used to afford,by using appropriate reagents, the ligands ppq and bpqpy ingood yields. The synthesis of ruthenium(I1) complexes with thesebidentate and tridentate ligands parallels the syntheticprocedure for the preparation of similar ruthenium(r1) com-plexes.'NMR, mass, IR, and UV-VIS spectral data support theformulation of the synthesized compounds.The ligands andtheir ruthenium(11) complexes show very complicated 'H NMRspectra. A complete NMR analysis and stereochemic studieJ. CHEM. SOC. DALTON TRANS. 1991 2547100 -l84 1Im/zPositive-ion FAB mass spectrum of [R~(bipy)~(ppq)][PF,]~ complex Fig. ITable 1 Selected IR (KBr disks) bands (cm-') of the synthesized compoundsC = CjC = N ring stretching1590s, 1575m, 1550ms, 1490m, 1475m,1440mw 1410m, 1360m1590s, 1 %Om, 1555s, 1497ms, 1485w,1450mw, 1420mw, 1360m1610mw, 1590mw, 1540w, 1470m, 1450m,1380w1590m, 1535mw, 1485w, 1450w, 1415w,1375wCompound (1 6W1360 cm-')PP9bqPYCRU(biPY)2(PP9)I2 +CRu@PqPY)212 +s = Strong, m = medium, w = weak.Aromatic C-H out-of-plane bending(9W560 cm-')890w, 800s, 780s, 760s, 710ms, 680m,625mw, 620m, 595m900m, 825ms, 780s, 765s, 710ms, 675w, 620w,585w840s, 770m, 735w, 705w, 560ms840s, 810w, 770m, 705mw, 560mof the ligands and complexes will be reported elsewhere.It isworth noting that the aromatic proton in the 3 position of thepyridine moiety in the ruthenium(I1) complexes displays aremarkable deshielding of ca. 0.4 ppm, as compared to the freeligands, which is considered diagnostic for their formation.Mass Spectroscopy.-The ligands are very stable to electron-impact (EI) decomposition, as reflected by very strongmolecular ion intensities, by the presence of relatively intensepeaks associated with doubly charged molecular ions, and by anegligible fragmentation pattern.The mass spectrum of ppq is dominated by peaks at rnjz 282(M", relative intensity 86%) and 281 ([A4 - HI+, base peak),the latter arising from a metastable supported loss of H' fromthe molecular ion. The most intense peak in the spectrum ofbpqpy is due to the molecular ion at rnjz 485.The second mostintense peak at m/z 242.5 (relative intensity 25%) results from adoubly charged molecular ion. The molecular ion undergoes ccfission relative to the central pyridine to generate comple-mentary ions at rnjz 281 (3) and 204 (12.4%). The positivecharge is mainly retained on the quinoline fragment.A rapid structural characterisation of the ruthenium(I1)complexes was achieved by FAB mass spectroscopy.Thepositive-ion FAB mass spectrum of [Ru(bipy),(ppq)][PF,],is reported in Fig. 1. It shows a diagnostically important peakat m/z 841 (base peak), corresponding to [Ru(bipy),(ppq)-(PF,)] +, which displays the expected isotopic pattern for a Ruatom. The loss of a PF, group from this ion generates the ionat rnjz 696, [Ru(bipy),(ppq)]", which is the second largest peakin the spectrum (relative intensity 53%). The third most intensepeak at m/z 348 (37%) is due to the doubly charged[Ru(bipy),(ppq)12+. Less-intense fragments at mjz 559 (1 1.8%),[R~(bipy),(PF,)]~+, and 414 (28%) [Ru(bipy),] +, are alsopresent, due to the sequential loss of ppq and PF, groups fromthe ion at m/z 841.The low-intensity peak at mjz 683 (4.6%) maybe associated with a dehydrogenated [Ru(bipy)(ppq)(PF,)] +species. This fragment ion undergoes sequential loss of PF, andbipy groups to generate dehydrogenated [Ru(bipy)(ppq)]' + and[Ru(ppq)]'+ species at mjz 538 (32) and 382 (22%) respectively.The positive-ion FAB mass spectrum of [Ru(bpqpy),]-[PF,], shows spectral features similar to those of [Ru-(bipy),(ppq)][PF,],. Thus, the highest observable set of peakscentred at m/z 1217 (41%) is due to [Ru(bpqpy),(PF,)]+. Thision decomposes by loss of a PF, group to give the fragment[Ru(bpqpy),]'+ at mjz 1072, which is the base peak in thespectrum. Other intense sets of peaks centred at m/z 536 (49)and 585 (48%) are due to the doubly charged [Ru(bpqpy),12+ion, and to the dehydrogenated [Ru(bpqpy)]' ' fragment,respectively.Infrared Spectra.-The IR spectra of the ligands ppq andbpqpy are similar (Table 1).They are characterised by aromaticC-H stretching bands between 3080 and 3010 cm-' and by aseries of overtone bands between 2000 and 1650 cm-' due to thepresence of monosubstituted benzene and/or pyridine deriv-atives. l 5The spectral region 160&1360 cm-' is complicated byquinoline and pyridine vibrations, but a series of six, strong ormedium, bands between 1600 and 1450 cm-' along with twoothers between 1420 and 1360cm-' can be assigned to quinolinebreathing vibrations. Finally, well resolved absorption bandsare present at lower frequencies which can be ascribed to the in-plane and out-of-plane ring deformations.' 7 3 1The IR spectra of complexes 1 and 2 are quite different fromthose of the free ligands (Table l), and show (i) a changed 1600-1360 cm-' spectral region with the disappearance or shift tohigher frequencies of the eight characteristic bands assigned tothe quinoline breathing vibrations of the free ligands, (ii) in the900-700 cm-' spectral region only two main bands at 770 and705 cm-' that can be assigned to the aromatic C-H out-of-planebending of the co-ordinated quinoline and pyridine rings.Thecomplex [Ru(bipy>,(ppq)][PF,], shows in this spectral regiona third band at 735 cm-' that is characteristic of a co-ordinatedbipy ring; two strong and medium, respectively, bands at 840and 560 cm-' are characteristic of a PF, - anion.lg Assignmentsof metal-ligand modes are hampered by a lack of data.Electronic Spectra.-The UV electronic spectra of the ppqand bpqpy ligands in methanol are shown in Fig.2, while theirmaxima and absorption coefficients are summarised in Tables 2548 J. CHEM. SOC. DALTON TRANS. 1991Table 2 Ultraviolet-visible spectral data for bidentate ligands and related mixed-ligand ruthenium(i1) complexes aCompound d, - IT* (pq or ppq) d, - n:* (bipy) n: --- n:*'P9 247 (34.0)PP9[Ru(bip~),(pq)]~+ 476sh 452 (10.5) 289 (51.6), 275 (49.7), 247 (35.8)CRU(biPY>2(PPS)I2 + 473sh 452 (1 5.3) 340sh, 323sh, 310sh, 290 (84.3), 282sh, 247 (43.6)334sh, 320sh, 302sh, 273 (16.1), 253 (26.5)h,,, in nm, error & 1 nm; E values in parentheses, in dm3 mol-' cm-' xTransitions for both bidentate ligands and bipyridine ligands are superimposed.' Calculated data from ref. 21. From ref. 22.Spectra were recorded in methanol solution at room temperature.Table 3 Ultraviolet-visible spectral data for tridentate ligands and related ruthenium(i1) complexesCompound dn - n:*bqPYbPqPY[Ru(bqpy)J2+[Ru(bpqpy),12+613sh, 562sh, 510 (9.0), 45610sh, 560sh, 518 (1 lS),473sh(7 .o>n:-'x*340 (17.1), 320 (31.0), 310 (30.2), 250 (78.7)338sh, 320sh, 313 (33.1), 253 (75.7)373 (53.9), 354 (36.5), 329sh, 309 (53.0), 257sh,249 (83.7)376 (47.3), 357sh, 340 (54.4), 312 (53.5),258 (73.2)' A, in nm, error & 1 nm; E values in parentheses, in dm3 mol-' cm x Spectra were recorded in methanol solution at room temperature.From ref.23.0.80.6Q,a Fg 0" 0.4 a0.20.0I240 280 320II I I240 280 320UnmFig. 2 Absorption spectra of the ppq (a) and bpqpy (b) free ligands inmethanol solution; c = 3.17 x and 1.47 x mol dm-3,respectivelyand 3, respectively. It is apparent that phenyl substitution on2-(2'-pyridy1)quinoline (pq) and 2,6-bis(2'-quinolyl)pyridine(bqpy) to produce ppq and bpqpy, respectively, results in asmall red shift of the energy of the .n -+ n* transition.20,21The absorption spectrum of [R~(bipy)~(ppq)]~ + ion [Fig.3(a)] shows an intense transition at 452 nm with a low-energyshoulder at 473 nm and a strong absorption at 290 nm.On thebasis of the similarity in energy and molar absorption coefficient(Table 2) with previously reported complexes such as[R~(bipy>~(pq)]~' and [Ru(bipy),]* +, the former absorp-tions are most likely d __+ n* metal-to-ligand charge-transfer(m.1.c.t.) transitions. The highest absorption at 290 nm isassigned as an intraligand t r a n ~ i t i o n . ~ ~ , ~ ~For the above reasons and in agreement with literaturethe two m.1.c.t. transitions at 473 and 452 nm, theintensities of which are weighted by the numbers of each ligandin the complex, can be assigned to the Ru+ ppq andRu -+ bipy c.t. transition, respectively. The UV-VIS spectrumof the [R~(bpqpy)~]~+ ion [Fig. 3(b)] shows an intensetransition at 518 nm with two low-energy shoulders at 560 and610 nm, while the ultraviolet region exhibits several strongbands with absorption coefficients between 47 300 and 73 200dm3 mol-' cm-' (Table 3).Similarities in the absorption spectra of the bpqpy complexcompared to that of bqpy,20 and correlation between electronicspectra and electrochemistry (see below), allow the conclusionthat the maximum at 518 nm can be associated to aRu --+ bpqpy c.t.transition. The absorption tail towards the red,with shoulders at 560 and 610 nm, already noted for otherquinoline-containing complexes,6b~20*28 is likely due to inter-chromophoric coupling, as pointed out by De Armond and co-w o r k e r ~ ; ~ ~ indeed the highest absorptions at 376, 340, 312 and258 nm can be assigned as intraligand transitions.The phenyl substitution on pq to give ppq does not seem toproduce any appreciable effect on the visible region of theabsorption spectrum of the mixed-ligand complex [Ru(bipy),-(ppq)12 + with respect to [R~(bipy)~(pq)]~ + .* I On the contrary,in the case of the homoligand ruthenium(I1) complex 2, thephenyl substitution on bqpy to produce bpqpy causes abathochromic (510 uersus 518 nm) and hyperchromic ( E 9000uersus 11 500 dm3 mol-' cm-') effect on the absorptionspectrum of [Ru(bpqpy),12+ with respect to [Ru(bqpy),j2 +(Table 3).20,23 It can be probably explained by the greaterelectronegativity of the phenylated ligand and by the presenceof resonance interactions.28Electrochemistry.-Differential pulse voltammetry (DPV)curves in MeCN are shown in Fig.4, and electrochemical datafor [R~(bipy)~(ppq)]~+ and [Ru(bpqpy),12+ complexes aresummarised in Table 4. For comparison the complex[Ru(bipy),12 + was also studied under identical experimentalconditions. For the last complex one oxidation and threemonoelectronic reduction waves, reflecting the addition ofelectrons to the three bipyridyl ligands, are observed. Theelectrochemical data obtained (Table 4) are in accord with thevalues of other similar compounds.The DPV curves of the complexes [Ru(bipy)2(ppq)]2f anJ. CHEM. SOC. DALTON TRANS. 1991 25490.8 iI I I I I I I I240 400 560UnmFig. 3 Ultraviolet-visible spectra of the complexes [Ru(bipy),-(ppq)I2+ (a) and [Ru(bpqpy),]'+ (b) in methanol solution; c =0.9 x lW5 mol dm-3 (five times more concentrated for visible spectra)for both complexes[Ru(bpqpy),12 + show one oxidation and three and four,respectively, reversible monoelectronic waves (Fig.4).A comparison of the Ered values of complex 1, with those of[R~(bipy)~],+, suggest that for 1, El reflects the reduction ofthe ppq ligand and E, and E , the reduction of the tworemaining bipyridyl ligands. The E2 and E, values for 1 aremore negative than those of El and E, for the complex[Ru(bipy),12+ because a negative charge is added to a pre-existing negative [Ru"((bipy),(ppq)-)] species.Further comparison of &ed data for complex 1 with those of[R~(bipy)~(pq)]~ + and [Ru(bipy),12 + shows quite different Elvalues for these complexes (Table 4).A positive shift is observedfor the first reduction potential of [R~(bipy)~(ppq)]'+ (- 1.071V) with respect to [Ru(bipy),(pq)I2+ and [Ru(bipy),12 + (El- 1.135 and - 1.330 V, respectively). The same positive shift isobserved for the El reduction potential of complex 2 (-0.831V) with respect to the [Ru(terpy),I2' (-1.430 V) (Table 4).{No electrochemical data are available in the literature for the[Ru(bqpy),12+ complex). The following waves can be assignedto the first reduction of the second bpqpy (E,), and to secondsuccessive reductions of the polyquinoline ligands (E, and E4).The differences between El and E, and E, and E4 (xO.6 V) arein agreement with this assignment.This experimental observation confirms that (owing to thepresence of a phenyl group) the existence of better resonanceinteractions favours reduction of the ligand and increase inoxidation potential of the metal (Table 4), and is in accord withthe electronic data showing a lowering in energy of the m.1.c.t.state.Furthermore, a plot of the difference between theoxidation potential and the first reduction potential (AE),uersus the absorption maximum of the m.1.c.t. band,,' for all the0.8 0.0 -0.8 -1.6E NFig. 4 Differential pulse voltammetry curves for [Ru(bipy),12+ (a),[R~(bipy),(ppq)]~ + (b), and [Ru(bpqpy),]'+ (c) complexes in 0.1 moldm3 NBu,ClO,-MeCN solutions. The signal at 409 mV is due to theferrocene-ferrocenium couple (see Physical Measurements)complexes reported in Table 4, was roughly linear so confirmingthe assignments given.Luminescence Propertiex-In fluid solution at room temper-ature the complex [R~(bipy)~(ppq)]~' strongly emits in all thesolvents used, whereas no emission was detected for [Ru-(bpqpy),], + up to 850 nm.Both complexes were luminescent ina MeOH-EtOH (4:l) rigid matrix at 77 K. Luminescencedecays were in all cases strictly monoexponential. Theluminescence energy maxima, lifetimes and quantum yields arecollected in Table 5.The emission of complex 1 is attributed to a triplet Ru + ppqcharge-transfer (3m.l.c.t.) excited state, either at room tempera-ture or 77 K, because of: (i) the luminescence lifetimes (Table5);' (ii) the blue shift of the energy of the emission maximumwith decreasing temperature;' (iii) the quenching of theluminescence lifetimes by dioxygen (Table 5); (iu) the fact thatthe Ru -+ ppq c.t.excited state lies at lower energy than that ofthe corresponding Ru- bipy state, as suggested by theelectrochemical results (see above).Ruthenium(I1) complexes with tridentate polypyridineligands are usually not luminescent in fluid solution at roomtemperature, because of the coming into play (by thermalactivation from the lowest excited state) of a low-lying metal-centred (,rn.c.> excited state, which leads to fast radiationlessdecay and/or ligand photodissociation. ',, The low-energ2550 J. CHEM. SOC. DALTON TRANS. 1991Table 4 Electrochemical data for ruthenium(I1) complex ions at room temperature aHalf-wave potential, E+/VComplex +3/+2 +2/+1 +1/0 O/-1 - l / - 2 Reference electrodeCRu(bipy)3I3+ 1.290 - 1.330 - 1.515 - 1.770 SCE[Ru(bipy),(pq)12 + 1.270 -1.135 -1.500 - 1.743 SSCEcRu(biPY),(PPq)lZ + 1.334 - 1.071 - 1.451 - 1.681 SCECRu(terpy)z12+1.280 - 1.430 SCECRu(bpqpy)212 + 1.406 -0.831 -1.096 -1.474 -1.719 SCEIn MeCN.SCE = Saturated calomel electrode, SSCE = sodium chloride saturated calomel electrode. ‘ Containingo. 1 mol dm-3 NBu,ClO,. Fromref. 30. From ref. 1.Table 5 Luminescence properties of the new complexes298 K “ 77 K bComplex h,,,/nm Tins @ h,,,/nm TIPSCRu(biPY)z(PPq)12 + 702 430 0.01 669 2.7(234)CRu(bPqPY),lZ + 697 5.8Deaerated acetonitrile solutions. In MeOH-EtOH (4: 1) rigid matrix. Aerated acetonitrile solution.position of the 3m.c. excited state in ruthenium(r1) complexeswith tridentate ligands is attributed to the fact that such ligandsare not suitable to provide the right octahedral co-ordinationsite for the Ru2+ ion.32 An exception to such a behaviour isshown by [ R ~ ( t p t e r p y ) ~ ] ~ +, where tpterpy is 4,4’,4”-triphenyl-2,2’:6’,2”-terpy1-idine,~~ in which an increased energy gapbetween the 3m.l.c.t.and 3m.c. excited states, due to mesomericinteractions, has been invoked to justify the room-temperaturelumine~cence.~~ Since in the [Ru(bpqpy),12 + complex a lower3m.l.c.t. excited-state energy with respect to [Ru(tpterpy),I2 +should be expected, as also confirmed by the low-temperatureemission energy (697 and 634 nm,23 respectively), we hoped thatcomplex 2 would emit at room temperature but this was not thecase.This could be due to a lowering in energy of the 3m.c.excited state because of steric hindrance introduced by thequinoline hydrogens of the 8’ position; for this reason noenhanced gain in energy gap between the 3m.l.c.t. and 3m.c.excited states is probably obtained in the studied complex withrespect to [ R ~ ( t e r p y ) ~ ] ~ +, and as a consequence no advantagein room-temperature emission properties is found.In a rigid matrix at 77 K, thermal activation of the 3m.c.excited state is not possible, and the complex exhibits a strongemission typical of triplet ruthenium --+ polypyridine c.t. levels.As far as the lifetime of the low-temperature emission isconcerned, it should be noted that complex 2 is a longer-livedemitter than 1, in spite of the expectation based on the energy-gap law.’ Our results are in agreement with those of Meyer andc o - ~ o r k e r s ~ ~ concerning the effect on the luminescence lifetimeof increasing delocalization in the acceptor ligand of the 3m.l.c.t.excited state.ConclusionTwo new ruthenium(r1) complexes with phenyl-substituted bi-and tri-dentate polypyridine ligands, 1 and 2, have beensynthesised and characterised. The results of an investigation ofthe luminescence properties and electrochemical behaviour hasshown that [Ru(bipy),(ppq)l2+ is a good candidate as aluminescent and redox-active species to be incorporated in apolymer polyquinoline- based backbone.Although the [Ru-(bpqpy),12 + complex is not emissive at room temperature, weare currently considering the replacement of one of the twotridentate bpqpy moieties with more suitable ligands, whichmay eventually lead to mixed-ligand ruthenium(I1) complexeswith better luminescence characteristics at room temperature.The synthesis and characterization of polyquinoline co-polymers and of related ruthenium(I1) complexes are underway.AcknowledgementsWe thank Professors V.Balzani and L. Fabbrizzi for helpfuldiscussions. This work was supported by the Minister0 dellaPubblica Istruzione.References1 See, for example, (a) A. Juris, V. Balzani, F. Barigelletti, S.Campagna, P. Belser and A. von Zelewsky, Coord. Chem. Rev., 1988,84,85; (b) T. J. Meyer, Ace. Chem. Res., 1989,22, 163.2 K.Kalyanasundaram, J. Kiwi and M. Graetzel, Helv. Chim. Acta,1978,61,2720; J. M. Lehn and J. P. Sauvage, Nouv. J. Chem., 1977,1,449; J. M. Lehn, J. P. Sauvage and R. Ziessel, Nouv. J. Chem., 1979,3,423; M. Graetzel (Editor), Energy Resources through Photochemistryand Catalysis, Academic Press, London, 1983.N. Vlachopulos, P. Liska, J. Augustynski and M. Graetzel, J. Am.Chem. Soc., 1988, 110, 1216; R. Dabestani, A. J. Bard, A. Campion,M. A. Fox, T. E. Mallonk, S. E. Webber and J. M. White, J. Phys.Chem., 1988,92,1872; R. Amadelli, R. Argazzi, C. A. Bignozzi and F.Scandola, J. Am. Chem. Soc., 1990,112,7099.B. Durham, W. J. Dressick and T. J. Meyer, J. Chem. Soc.. Chem.Commun., 1979,381.J. M. Kelly, D. J. McConnell, C. Ohuigin, A. B. Tossi, F.Kirsch-DeMesmaeker and J. Nasielski, J. Chem. Soc., Chem. Commun., 1987,1821; A. M. Pyle, J. P. Rehmann, R. Meshoyrer, C. V. Kumar, N. J.Turro and J. K. Barton, J. Am. Chem. Soc., 1989, 11, 3051; A. B.Tossi and J. M. Kelly, Photochem. Photobiof., 1989,49, 545.(a) Y. Fuchs, S. Lofters, T. Dieter, W. Shi, R. Morgan, T. C. Strekas,H. D. Gafney and A. I). Baker, J . Am. Chem. Soc., 1987, 109,2691;(b) G. Denti, S. Campagna, L. Sabatino, S. Serroni, M. Ciano and V.Balzani, Znorg. Chem., 1990,29,4750; (c) F. Scandola, M. T. Indelli,C. A. Bignozzi and C. Chiorboli, Top. Curr. Chem., 1990,158,73; ( d )W. R. Murphy, jun., K. J. Brewer, G. Gettliffe and J. D. Petersen,Inorg. Chem., 1989, 28, 81; (e) K. Kalyanasundaram and Md. K.Nazeeruddin, J. Chem.Soc., Dalton Trans., 1990,1657; (f) V. Balzaniand F. Scandola, Supramolecular Photochemistry, Ellis Horwood,Chichester, 1991.J. N. Younathan, S. F. McClanahan and T. J. Meyer, Mucro-molecules, 1989, 22, 1048.G. F. Strouse, L. A. Worl, J. N. Younathan and T. J. Meyer.J. Am. Chem. Soc., 1989, 111, 9101; L. A. Worl, G. F. Strouse,J. N. Younathan, S. M. Baxter and T. J. Meyer, J. Am. Chem. Soc.,1990,112,7571.F. A. Bottino, A. Mamo, A. Recca, J. P. Droske and J. K. Stille,Macromolecules, 1982, 15, 227J. CHEM. SOC. DALTON TRANS. 1991 255 110 J. K. Stille, Macromolecules, 1981, 14, 870.1 1 P. A. Lay, A. M. Sargeson and H. Taube, Inorg. Synth., 1986, 24,12 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971,75,991.13 K. Nakamaru, Bull. Chem.SOC. Jpn., 1982,55,2697.14 E. A. Seddon and K. R. Seddon, The Chemistry of Ruthenium, Elsevier,15 G. L. Cook and F. M. Church, J. Phys. Chem., 1957,61,458; H . E.16 L. J. Bellamy, The Infrared Spectra of Complex Molecules, Chapman17 V. Carassiti, A. Seminara and A. Seminara-Musumeci, Ann. Chim.18 N. Neto, M. Muniz-Miranda, L. Angeloni and E. Castellucci,19 R. A. Nyquist and R. 0. Kagel, Infrared Spectra of Inorganic20 D. M. Klassen, C. W. Hudson and E. L. Shaddix, Inorg. Chem., 1975,21 D. M. Klassen, Inorg. Chem., 1976, 15,3166.22 D. M. Klassen, Chem. Phys. Lett., 1982,93,383.23 M. L. Stone and G. A. Crosby, Chem. Phys. Lett., 1981,79,169.24 M. Maestri and M. Graetzel, Ber. Bunsenges. Phys. Chem., 1977,81,291.Amsterdam, 1984.Podall, Anal. Chem., 1957,29, 1423.and Hall, London, 1980.(Rome), 1964,54, 1025.Spectrochim. Acta, Part A, 1983,39,97.Compounds, Academic Press, London, 1971.14,2733.504.25 S. Anderson, K. R. Seddon, R. D. Wright and A. T. Cocks, Chem.26 D. P. Rillema, G. Allen, T. J. Meyer and D. Conrad, Inorg. Chem.,27 R. P. Thummel and Y. Decloitre, Inorg. Chim. Acta, 1987, 128,245.28 R. P. Thummel, V. Hedge and Y. Jahng, Inorg. Chem., 1989,28,3264.29 M. L. Myrick, R. L. Blakley and M. K. De Armond, J. Phys. Chem.,1989,93,3936; M. L. Myrick, M. K. De Armond and R. L. Blakley,Inorg. Chem., 1989,28,4077.30 Y. Ohsawa, K. W. Hanck and M. K. De Annond, J. Electroanal.Chem., Interfacial Electrochem., 1984,175,229.31 B. Durham, J. V. Caspar, J. K. Nagle and T. J. Meyer, J. Am. Chem.Soc., 1982,104,4803; J. Van Houtenand R. J. Watts, Inorg. Chem., 1978,17,3381; L. De Cola, F. Barigelletti and M. J. Cook, Hefu. Chim. Acta,1988,71,733 and refs. therein.32 F. Barigelletti, L. De Cola, V. Balzani, P. Belser, A. von Zelewsky, F.Vogtle, F. Ebmeyer and S. Grammenudi, J.Am. Chem. SOC., 1989,111,4662.33 J. R. Kirchhoff, R. McMillin, P. A. Marnot and J. P. Sauvage, J. Am.Chem. SOC., 1985,107,1138.34 S. Boyde, J. F. Strouse, W. E. Jones, jun. and T. J. Meyer, J. Am.Chem. SOC., 1990,112,7395.Phys. Lett., 1980, 71, 220.1983,22,1617.Received 14th November 1990; Paper 0/05 125