Octa-alkoxy phthalocyanine and naphthalocyanine derivatives: dyes with Q-band absorption in the far red or near infrared

摘要

J. CHEM. SOC. PERKIN TRANS. I 1988 Octa-alkoxy Phthalocyanine and Naphthalocyan ine Derivatives: Dyes with Q-Band Absorption in the Far Red or Near Infrared Michael J. Cook,* Adrian J. Dunn, Steven D. Howe, and Andrew J. Thomson Schoolof Chemical Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ Kenneth J. Harrison Royal Signals and Radar Establishment, St. Andrews Road, Great Malvern, Worcs, WR 143PS The lithium alkoxide-catalysed cyclic tetramerisation of various 3,6-dialkoxy-4,5-dichlorophthalo-nitriles, 1,4-dialkoxynaphthalene-2,3-dicarbonitriles and 3,6-dialkoxyphthalonitriles to give the corresponding metal -free octa-al koxyoctac hloropht halocyani nes, octa -al koxynapht halocyanines and octa -alkoxyphthalocyani nes is described. An unexpected trans-alkoxylation reaction occurs during the cyclisation of the first two series of precursors.Metal-free phthalocyanines and naphthalo- cyanines have been converted into derivatives containing various metal ions. Compounds show 0-band absorption in the region 739-862 nm in toluene solution. The fluorescence spectra of selected examples are reported. The solubility of some of the compounds has been measured in a formulation of liquid crystal materials. Compounds which absorb strongly at wavelengths of laser light can, in principle, be exploited as guest dyes dissolved in liquid crystalline host materials in a laser addressed system. Such devices utilize absorption of laser energy by the dye to cause local heating which alters optical properties in otherwise transparent liquid crystals.Particular applications are in laser addressed storage systems and projection displays in which light is directed through a cell containing the material and projected onto a screen. Ga,Al,-,As lasers (where x = 0-1) provide laser light in the range of ca. 850 nm for gallium arsenide down to ca. 750 nm as the aluminium content is increased. Thus light-absorbing compounds are required which match these lasers; the materials should also be at least partially soluble in the liquid crystal medium. Phthalocyanines show strong absorption in the visible region (Q-band), e.g. metal-free phthalocyanine, H,Pc, I,,,. 665 and 698; copper phthalocyanine, CuPc, I,,,. 678 nm.' The band is shifted further to the red when substituents are introduced onto the benzene rings, particularly at sites a to the point of fusion to the heterocyclic ring (the '3,6' positions).2 Linear benzoannulation also gives rise to bathochromic shifts as exemplified by 2,3-naphthalocyanine (NPc), I,,,.780 nm.3 There is, therefore, potential for tuning the Q-band absorption to match the wavelengths of GaAlAs laser light. However, the problem of the low solubility of the Pc ring system in organic solvents also needs to be overcome if the application of these materials in the devices outlined above is to be realised. As part of a research programme into Pc derivatives we have addressed the problem of insolubility by introducing bulky or long chain substituents at the apositions. Substituents so placed should cause substantial disruption of the strong lattice forces of the parent Pc and hence help confer solubility.Considerable success has been achieved with straight-chain alkyl groups4 The present paper describes the synthesis and spectroscopic properties of Pc and NPc derivatives bearing alkoxy groups with chain lengths varying between C, and CI2. These groups give rise to substantial bathochromic shifts of the Q-band. We also report the solubility of representative materials in liquid crystals. Results and Discussion Preparative Work.-The compounds originally sought in this study fall into three series, classified according to the substituents or modification of the Pc structure. We refer to the first series, investigated as the metal-free derivatives and in one case as the copper complex, as octachloro-octa-alkoxy-phthalocyanines (Cl-RO),H,Pc (1) and (Cl-RO),CuPc (2).The second and third series, obtained as the metal-free and in some instances as copper, zinc, or nickel complexes, we designate respectively as octa-alkoxynaphthalocyanines (RO),H,NPc (3)and (RO),CuNPc (4), and octa-alkoxy- phthalocyanines (RO),H,Pc (5), (RO),CuPc (6), (RO),ZnPc (7),and (RO),NiPc (S). A convenient method for preparing Pc derivatives is to treat a phthalonitrile with a lithium alkoxide. This induces the required cyclic tetramerisation reaction to give the Pc as the lithiated derivative which on acidic work-up is converted into the metal- free analogue.Thus, in principle, for the present study the immediate precursors to the Pc and NPc derivatives are the appropriately substituted dialkoxy dinitriles (9),(lo), and (11). These were prepared by standard alkylations of the dicyano- hydroquinones (12), (13),and (14).Most were recrystallised for combustion analysis (see Table 1). However, in two cases (see Experimental section) the product isolated from the reaction mixture was used directly in the tetramerisation reaction without further purification. In these cases, confirmation of structure was based on n.m.r. and i.r. spectroscopic data. Previously, Witkiewicz et aL5 converted (lla)into (5a)using lithium pentanolate in pentanol: they subsequently obtained from (5a)the copper and zinc complexes.In the present work, 4,5-dichloro-3,6-dimethoxyphthalonitrile(9a)was treated with lithium pentanolate in pentanol and the reaction worked up in acetic acid. The resulting product showed an unexpectedly low m.p., 71-73 OC, and was readily soluble in toluene and methylene dichloride. The material showed u.v.-visible absorption bands consistent with formation of the Pc ring system (i.e. Soret and Q-band). However, the 'H n.m.r. spectrum revealed that the product was not the expected oc_tamethoxy compound (la),there being signals for protons in pentyloxy side-chains as well as a singlet for a methoxy side- chain. Microanalytical data on the material showed that the chlorine atoms had been retained. Thus at some stage during the reaction an unexpected trans-alkoxylation had occurred giving rise to incorporation of pentyloxy groups at the expense of the methoxy substituents.Integration of appropriate signals in the n.m.r. spectrum revealed that ca. 75 of the methoxy groups had been exchanged by pentyloxy groups. Using the 2454 J. CHEM. SOC. PERKIN TRANS. I 1988 CI CI CI CI (1) M = H, H; (3) M = H, H; (5) M = H, H; (6) M = CU; a R=Me a R=Et a R=Me a R=Pr b R=Et b R=Pr b R=Et b R=Bu c R=Pr c R=Bu c R=Pr c R = Pentyl d R=Bu d R = Pentyl d R=Bu d R = Octyl e R = Pentyl e R = Octyl e R = Pentyl e R = Dodecyl f R = Hexyl f R = Pent-4-enyl (2) M = Cu, R = Pentyl (4) M = Cu, R = Pentyl g R = Heptyl RO RO ROWCN'CN RO RO RO (9) a R = Me (10) a R = Me (11) a R = Me b R=Et b R=Et b R=Et R=Pr c R=Pr c R=Pr d R=Bu d R=Bu d R=Bu e R = Pentyl e R = Octyl e R = Pentyl f R = Hexyl (12) R = H (13) R = H g R = Heptyl h R = Octyl i R = Nonyl j R = Decyl k R = Dodecyl 1 R = Pent-4-enyl m R = 3-Phenyl-ProPYl (14) R = H same reaction conditions, 1,4-dimethoxynaph t halene-2,3 -dicarbonitrile (10a) afforded a soluble red-brown material having both a Soret band and a Q-band in the u.v.-visible spectrum.The 'H n.m.r. spectrum showed that trans-alkoxylation had again occurred with the ratio of pentyloxy groups to methoxy groups being 9: 1. In a subsequent reaction exchange was complete as judged from the 'H n.m.r. spectrum and satisfactory analytical data. The cyclic tetramerisation of (9a) and (10a) was investigated in other alcohols using the corresponding lithium and, in one case, sodium alkoxide as base.Results showing the extent of the alkoxide exchanges in the derived (Cl*RO),H,PC'S and (RO),H,NPc's are given in Table 2. In subsequent experiments 4,5-dichloro-3,6-dipropoxyphthalonitrile(9c) was cyclised in pentan-1 -01-lithium pentanolate to give a mixed pentyloxy/ h R = Octyl (7) M = Zn, R = Pentyli R = Nonyl j R = Decyl (8) M = Ni, R = Pentylk R = Dodecyl I R = Pent-4-enyl m R = 3-Phenylpropyl propoxy (Cl*RO),H,PC (ratio of groups 87: 13). There was no evidence of alkoxide exchange when (Cl-MeO),H,Pc or (MeO),H,NPc were treated with lithium or sodium pentano- late in pentan-1-01.From this we deduce that the observed displacements probably occur via reactions on either the starting dinitrile or an intermediate. Samples of (C1-RO),H2PC and (RO),H,NPC containing but one type of alkoxy group were prepared in a subsequent series of reactions in which the dialkoxy dinitrile precursors (9) and (10) were treated with the corresponding alkoxide/alcohol (see Table 3). Where direct comparisons are possible it is apparent that yields of recovered product are higher for the (Cl*RO),- H,Pc series. A problem arose when cyclising the longer chain 1,4-dialkoxynaphthalene-2,3-dicarbonitrile(10e) because of the low reactivity of lithium in the long-chain alcohol. This was overcome by generating the lithium alkoxide by treating the alcohol with a solution of 1.5~butyl-lithium.3,6-Dialkoxyphthalonitriles (11) were converted into the corresponding (RO),H,Pc's (5)using either lithium pentanolate in pentan-1-01 or lithium butoxide in butan-1-01 (Table 3). There was no evidence of trans-alkoxylation in this series of reactions. Thus the trans-alkoxylation reaction is apparently promoted by the presence of the electron-withdrawing chlorine substituents and benzo fusion, features consistent with an S,Ar mechanism. The copper, zinc, and nickel complexes reported in Table 4 were prepared from the metal-free derivatives and the appropriate metal acetate using quinoline, butan-1-01, or pentan-1-01 as solvents and heating the solution to reflux. Although reaction temperatures were lower using the alcohols as solvent, yields were higher, largely because of the greater ease of recovering the product.Electronic Spectra.-The Pc system is characterised 7,8 by strong absorption bands in the U.V. region (the Soret band) and in the visible region (the Q-band); low intensity bands in the J. CHEM. SOC. PERKIN TRANS. I 1988 2455 Table 1. Preparation of some 3,6-dialkoxy-4,5-dichlorophthalonitriles(9), 1,4-dialkoxynaphthalene-2,3-dicarbonitriles(lo), and 3,6-dialkoxy- phthalonitriles (11) from the dicyanohydroquinones (12), (13), and (14) Alkylating agent Time (h) Yield (3 M.p. ("C) Molecular formula I C Found (77) H N I C Requires (?o) H A N CH2N2 0.75 67 186' EtI 60 55 97 50.7 3.4 9.75 50.5 3.5 9.8 PrI 60 48 60 53.7 4.7 8.75 53.7 4.5 8.95 BuI 56 52 51 56.5 5.3 8.25 56.3 5.3 8.2 EtI CH2N2 PrI Bul Octyl I EtI PrI BuI Pentyl I Hexyl I Heptyl I Nonyl I Decyl I Dodecyl I CH2=CH(CH2),I Ph(CH2)3I 72 60 60 60 60 48 60 60 60 60 60 60 65 65 60 0.5 80 40 43 58 42 48 40 50 58 48 52 47 49 47 42 35 187* 169-1 71 9 1-93 67-69 38 203 198 193 172 164 153 151 142 137 178 170 cl gH 14N202 1 8H 1BN202 C20H22N2O2 C12H12N2Oz C28H3BN202 C14H 16N202 C16H20N202 C18H24N202 C20H28N202 C22H32N202 C26H40N202 c2 8H44N 2O2 C32H52N202 C18H20N2O2 C26H24N202 71.9 73.35 74.2 77.3 66.5 68.7 70.4 72.2 73.3 73.9 75.3 76.0 77.5 72.8 78.65 5.3 6.1 6.95 8.8 5.6 6.7 7.5 7.95 8.45 9.0 9.7 10.1 10.75 6.9 5.9 10.4 9.5 8.5 6.3 12.9 11.5 10.2 9.3 8.5 7.7 7.1 6.3 5.7 9.45 7.0 72.2 73.4 74.5 77.4 66.65 68.8 70.55 72.0 73.1 74.1 75.7 76.3 77.4 72.95 78.75 5.3 6.2 6.9 8.8 5.6 6.6 7.4 8.05 8.6 9.05 9.8 10.05 10.5 6.8 6.I 10.5 9.5 8.7 6.45 12.95 11.5 10.3 9.3 8.5 7.85 6.8 6.4 5.65 9.45 7.1 a Starting material.Straight-chain alkyl groups are used throughout. Lit.,6 187 "C. Lit.,6 189 OC. Table 2. Reactions of 4,5-dichloro-3,6-dimethoxyphthalonitrile(9a)and substituents located x to the point of fusion with the heterocyclic 1,4-dimethoxynaphthalene-2,3-dicarbonitrile(1Oa) with ROH/RO- to rings. A broadly comparable shift is apparent in the Pc series give (C1.MeOiRO),H2Pc and (MeO/RO),H,NPc where (RO),H,Pcs absorb at ca. 740 and 760 nm, well to the red of the Q-band in H,Pc 665 and 698 nm.' In contrast, a Pc Ratio of Me0 :RO derivative fused uia eight ether linkages at the '4,5-positions' (to Time Temp.groups four crown ether moieties) shows Q-band absorption at 690 Entry SM Solvent Base (h) ("C) in product nm.9 That the Q-band absorption is more red shifted by A (9a) EtOH EtOLi 0.75 150 1 :6.5" substituents at the 3,6-positions than by those at the 43- B (9a) PentylOH PentylOLi I Reflux 1 :7b positions is apparent from earlier studies. Thus octa-3,6-chloro (9a) PentylOH PentylONa 0.5 Refux 1:3b CuPc shows A,,,, 705 nm, 10 nm to the red of the Q-band in D (IOa) EtOH EtOLi 0.75 150 1:8.8b octa-4,5-chloro CUPC.~' Similarly, the Q, and Q, bands in E (IOa) PrOH PrOLi 0.75 150 1:9.7b octa-3,6-butyl H,Pc, 695 and 727 nm,4 are to the red of those F (IOa) BuOH BuOLi 0.5 Reflux 1 :34b in octa-4,5-butyl H,Pc, 673 and 708 nm." However, the G (IOa) PentylOH PentylOLi 0.5 Reflux 1:9,bO:1C magnitude of the effect is clearly much larger when the " Estimated by C, H, N elemental analysis data. Estimated from 'H substituent involves an ether linkage.Substantial red shifts have n.m.r. spectral data. No Me0 signal in 'H n.m.r. spectrum. Material also been reported for Pcs bearing sulphide linkages at the gives satisfactory C, H, N analysis for (PentylO),H,NPc, see Table 3. 3,6-positions.' The Q-bands for the (CbRO),H,PCS are marginally to the blue of those for the corresponding (RO),H,PCS. Data obtained for the former series also show a chain-length dependence. Thus (C1*MeO)8H,PC, in particular, visible region to shorter wavelength of the Q-band are vibronic absorbs at shorter wavelengths than the derivatives bearing in origin.Metal Pcs and metal-free Pcs have D,,,and D,,, longer chains. symmetry respectively and the degeneracy of the lowest-energy Splitting for the Q-band absorption in the spectra of the singlet state in the former is lifted in the latter by a rhombic metal-free compounds differs from one series to another. distortion. Thus unlike the spectra of metal Pcs, those of Among the (Cl*RO)amp;,PCS the Q, and Q, bands are best metal-free derivatives may show a characteristic splitting of the resolved when RO is methoxy or ethoxy. The values for A are Q-band into the Q, and Q, components provided that the comparable (480 and 490 cm-').However, when RO is rhombic distortion is larger than the optical bandwidth. pentyloxy the Q, absorption appears only as a shoulder. All of Q-Band absorption data obtained for representative the (RO),H,Pc compounds examined as solutions in toluene compounds in toluene solution are collected in Table 5. In show two well resolved lines. Values for A within this series addition to wavelengths, the energies and energy separation, A, again show no significant variation (39-30 cm-') but are of the Q, and Q, bands are given in the cases where splitting is lower than those for the (Cl.RO),H,Pcs. Spectra obtained of observed. (RO),H,Pcs in dichloromethane show loss of resolution of the The variations in A,,,. in Table 5 reveal how benzoannulation, two bands which is probably due to aggregation in this solvent.substituents, and central ion provide a means of tuning the Spectra recorded of lo4 and 10-5~solutions in dichloromethane wavelength of the Q-band absorption in the far red-near i.r. are identical in shape implying that if aggregation is indeed the region of the spectrum. The largest bathochromic shift is cause then it is present even at 10-5~concentration. Members of observed for the (RO),NPCS. Comparison of the I,,,,,. 862 nm in the (RO),H,NPc series show only a single band even in toluene these compounds with that in unsubstituted naphthalocyanine as does H,NPc itself in the solvent ~hloronaphthalene.~ The A,,,, 780 nm3 illustrates the sensitivity of the Q-band to alkoxy magnitude of A is a measure of the departure of the system from 2456 J.CHEM. SOC. PERKIN TRANS. I 1988 Table 3. Preparation of some (C1*RO)8H2PCrsquo;S (l), (RO),H,NPcrsquo;s (3), and (RO),H,Pcrsquo;s (5) Compound ROH/ Found Requires ()amp; ROLi No. Rob (ROH) CHNCHN (la) Me0 MeOH 46.2 2.6 10.8 46.6 2.5 10.9 (lb) EtO EtOH 50.7 3.6 9.7 50.45 3.7 9.8 (lc) Pro PrOH 53.9 4.6 8.8 53.6 4.65 8.9 (Id) BuO BuOH 55.9 5.4 8.1 56.2 5.5 8.2 (le) PentylO Pent ylOH 58.8 6.0 7.7 58.5 6.1 7.6 (3a) EtO EtOH 71.6 5.5 10.4 72.3 5.1 10.5 (3b) Pro PrOH 72.65 6.3 9.3 73.3 6.3 9.5 (3c) BuO BuOH 74.15 7.15 8.65 74.4 7.0 8.7 (3d) PentylO PentylOH 75.0 7.7 7.8 75.3 7.6 8.0 (3e) OctO OctylOH 77.2 9.3 6.3 77.3 8.9 6.45 (5b) EtO PentylOH 67.0 6.1 12.5 66.6 5.8 12.9 (5c) Pro PentylOH 68.8 6.6 11.4 68.7 6.8 11.4 (5d) BuO BuOH 70.4 7.7 10.0 70.4 7.6 10.2 (5e) PentylO Pent ylOH 71.8 8.1 9.3 71.8 8.2 9.3 (5f) Hex0 Pent ylOH 72.65 8.7 8.7 73.0 8.7 8.5 (5g) HepO PentylOH 73.9 9.2 8.0 74.0 9.2 7.85 (5h) OctO PentylOH 74.5 9.7 7.4 74.85 9.55 7.3 (5i) NonO Pent ylOH 75.2 9.75 7.0 75.6 9.9 6.8 (3) DecO PentylOH 75.95 10.4 6.45 76.2 10.1 6.35 (5k) DodecO PentylOH 77.0 10.8 5.85 77.3 10.6 5.6 (51) Pent-4-enylO (111) PentylOH 72.5 7.2 9.5 72.8 7.0 9.4 (5m) Ph(CH2),0 (llm) PentylOH 78.3 6.0 6.7 78.65 6.2 7.05 SM = starting material.R = straight chain. As reported in Table 2. Table 4. Preparations of metal derivatives of some alkoxy substituted phthalocyanines by treating the metal-free derivative with the appropriate metal acetate Compound Found () Requires () -Time Temp. Yield Molecular r-A-, No.RO Metal Solvent (h) (ldquo;C) () M.p. (ldquo;C) formula C H N C H N (2) PentylO cu Pent ylOH 0.5 Reflux 78 300 C72H8 8C18CuN808 56.4 5.6 7.5 56.1 5.75 7.3 (4) PentylO cu Quinoline 1.o Reflux 23 292-294 C88H 104CuN808 71.9 7.4 7.2 72.1 7.15 7.6 (decomp.) (6a) Pro cu BuOH 0.5 Reflux 81 300 64.6 6.2 10.7 64.6 6.2 10.8 (6b) BuO cu BuOH 0.5 Reflux 77 2-201 67.1 7.3 9.4 66.7 7.0 9.7 (6c) PentylO cu PentylOH 0.5 Reflux 85 173.5-1 74.5 68.4 7.6 8.8 68.35 7.65 8.9 (6d) OctylO cu PentylOH 0.5 Reflux 81 69 71.7 9.1 7.1 72.0 9.1 7.0 (6e) DodecylO Cu Pentyl OH 0.5 Reflux 79 52-53.5 74.85 10.4 5.4 75.0 10.2 5.5 (6f) Pent-4-enylO Cu PentylOH 0.5 Reflux 78 171.5-173 69.0 6.8 8.9 69.2 6.45 9.0 (7) PentylO Zn Pent ylOH 0.5 Reflux 71 139-141 68.5 7.4 9.0 68.25 7.6 8.8 (8) PentylO Ni PentylOH 0.5 Reflux 68 198-200 68.65 7.6 8.7 68.6 7.7 8.9 D,, symmetry., The splittings in metal-free tetra-azaporphin is For (C,H, 10)8H2P~ (Se) in toluene at room temperature, the 2 100 cm-rsquo;.Fusion of four benzene rings to this system to give emission is at h,,,, 771 nm (uncorrected). the Pc nucleus shifts the Q-band to the red as the conjugation is extended out to the benzene rings. It follows that the Solubility in a Nematic Liquid Crystal.-The long wavelength perturbation of the D,, symmetry by the two central hydrogens Q-band absorption and the window in the visible region which becomes less significant and the Q-band splitting is are characteristic of the present compounds can, in principle, be correspondingly lowered to 730 cm-rsquo;.Thus, there is a exploited in laser addressed systems. With the exception of the correlation between the energy of the centroid of the Q-bands octa-methoxy derivative (la), which is only sparingly soluble in and the energy splitting of the bands, the lower the energy the chloroform and toluene, the compounds prepared in this study smaller the value of A. The incorporation of substituents to give show satisfactory solubility in aromatic hydrocarbon solvents, the present series continues the trend, the Q-band splitting chloroform, and dichloromethane. Quantitative room-temper- decreasing on going from (Cl=EtO),H,PC to (EtO),H,PC as ature solubility data (w/w) were obtained for (C,H ,O),H,Pc the Q-band is shifted further to the red.The apparent absence of (5e) in CHCl, (21y0),xylene (lo;), and 2-ethoxyethyl acetate Q-band splitting in the spectra of the (RO),H,NPcs may, (0.57;) and for (C,,H,,O),H,Pc (5k) in xylene (10). The therefore, arise through further continuation of this effect. solubility in simple solvents prompted us to investigate the Fluorescence spectra were recorded for an example of a metal- solubility of samples in the nematic liquid crystal E7. The latter free derivative from each of the three series. (Cl-MeO),H,Pc is a commercially available (B.D.H. Chemicals, Poole, Dorset) (la) and (C,H, ,o),H,NPc (3d) were measured at room formulation of cyanobiphenyls and cyanoterphenyls. Twelve temperature as solutions in chloroform and values for the samples were investigated including two mixed methoxy/alkoxy corrected h,,,, emission are 745 and ca.890 nm respectively. materials, namely the products from the entries A and F in J. CHEM. SOC. PERKIN TRANS. I 1988 2457 Table 5. Q-Band absorption data for some (Cl*RO),Pcs, (RO),NPcs, and (RO),PCS hmax./nm(E x AI bsol; 1 1 No. Abbreviation Solvent QY QX QY Alcm-' " QX (la) (CbMeO),H,PC Toluene 71 1 736 (b) 14 070 13 590 480 (lb) (CbEtO),H,PC Toluene 726 (1.20) 753 (1.35) 13 770 13 280 490 (le) (CI*PentylO),H,Pc Toluene -735 (s) 756 (1.36) (2) (CI.PentylO),CuPc Toluene 739 (1.35) (3C) (BUO),H,NPC Toluene 862 (1.81) (3e) (OCtylO),H ,NPC Toluene 862 (1.82) (4) (PentylO),CuNPc Toluene 849 (2.34) (Sb) (EtO),H,Pc Toluene 734 (1.16) 758 (1.38) 13 620 13 190 430 (5C) (PrO),H,PC Toluene 737 (1.17) 760 (1.35) 13 570 13 160 410 (Bu0)8H2Pc Toluene 738 (1.13) 761 (1.34) 13 550 13 140 410 (5e) (Pent ylO),H ,Pc Toluene 738 (1.20) 762 (1.39) 13 550 13 120 430 (Sh) (OCty10)8H 2pc Toluene 740 (1.22) 762 (1.42) 13 510 13 120 390 CH,CI, (5k) (6d) (7) (Dodecy lO),H ,Pc (OctylO),CuPc (PentylO),ZnPc CH,Cl, CH,Cl, CH,Cl, (8) (PentylO),NiPc Toluene CH,Cl, 'Rhombic splitting (Q, -Q,).Material incompletely dissolved. Table 6. Solubility of materials and A,,,, for the Q-band absorption in nematic liquid crystal E7" at 20 OC Compound r A , No. Abbreviation Solubility (Wh) Lax.inm (Cl.EtO/MeO),H,Pc 0.1 746 ((21.Pent y10) ,H ,Pc 0.4 762 (Cl-PentylO),CuPc 2.7 754 (BuO/MeO),H,NPc 0.2 866 (PentylO),H,NPc (Oct y lo),H,NPc (PentylO),H,Pc (Octy lo),H ,Pc (DodecylO),H,Pc 0.3 0.1 1.3 2.5 1.7 871 874 770 77 1 77 1 (OCt y lO),CUPC 1.5 759 (PentylO),ZnPc 1.1 75 1 (PentylO),NiPc 1.8 748 'E7 Is a formulation of cyanobiphenyls and cyanoterphenyls supplied by BDH Chemicals, Poole, Dorset, U.K. Identifying letter refers to the product of that entry in Table 2. Table 2. The solubilities at 20 "C,expressed as a percentage by weight of E7, are given in Table 6. Solubilities are in the range 0.1-2.5 (w iw). Members of the octa-alkoxy Pc series (5)-(8) are the most soluble of the materials examined. There are fluctuations with chain-length and the highest solubility of those investigated was recorded for the octa-octyloxy derivative (5h).The Q-band absorption in each series undergoes a small bathochromic shift in the liquid crystal medium relative to toluene. From the point of view of the application in mind the modest solubility is largely offset by the advantageously high extinction coefficient of the Q-band. Thus the 1.3 (w/w) solution of the (C,H, 10)8H2Pc (5e) in E7 has an absorbance of 1.7 at A,,,,,. 770 in a 12 pm film aligned homeotropically (director orthogonal to plate) using a chrome complex agent. The absorbance minimum in the visible is less than 0.1. Under the same conditions, even the 0.2",, solution of the product of entry F, Table 2, shows an absorbance of 0.6 at 850 nm.The combination of strong near- i.r. absorbance and good transmission in the visible region, which are characteristics of 767 (1.38) 768 (1.45) 752 (1.91) 748 (1.32) 734 (1.66) 742 (1.69) the dyes examined in this study, is excellent for exploitation in a liquid crystal display addressed thermally using a semiconductor laser. Conclusions There is considerable scope for tuning the Q-band absorption of the Pc and NPc ring system to wavelengths in the far red and near- i.r. region of the spectrum. This can be achieved through the introduction of eight alkoxy groups at the benzenoid rings at sites IX to the point of benzo-fusion to the heterocyclic rings. Comparison of the (Cl*RO),H,Pcs and the (RO),H,Pcs shows that the presence of the chlorine atom at the 4,5-positions causes a small blue shift.The Q-band absorptions in these Pc derivatives varies between 711 and 736 to 740 and 762 nm in toluene solution. (RO),H,NPcs Absorb at 862 nm in toluene solution. Introduction of metal ions into the centre of both the Pc and NPc ring system offers a means of finer tuning of the wavelengths. All but the shortest alkoxy chain derivatives show good solubility in toluene, xylene, chloroform, and methylene dichloride and between cu. 0.1 and 2.5 (w/w) solubility at 20 "C in nematic liquid crystal E7. Experimental Materiuls.-The following were prepared by literature routes: 2,3-dichloro-5,6-dicyanohydroquinone(12) (9779, m.p.290 "C (lit.," 300 "C) by sodium metabisulphite reduction of the corresponding quinone, 2,3-dicyanonaphthalene- 1,4-diol (13) (62), m.p. 300 "C (lit.,6 300 "C) from 2,3-dichloro-1,4-naphthoquinone and KCN.6*' 2,3-Dicyanohydroquinone (14) was obtained from a commercial source (Aldrich Chemical Co. Ltd.). Alkjhtions.-Procedure (a) using diuzomethune. In a typical reaction, 2,3-dichloro-5,6-dicyanohydroquinone(12) (1 5 g) was suspended in ether (150 ml) and the mixture cooled to the temperature of an ice-salt bath. A solution of diazomethane (6 g) in ether was added with stirring over 15 min after which the mixture was evaporated to dryness (rotary evaporator/fume hood). The residue was recrystallised from ethanol to afford 43- 2458 dichloro-3,6-dimethoxyphthalonitrile(9a) (1 1.2 g, 67), m.p.187 "C (lit.,6 189 "C). Procedure (b) using alkyl halides. In a typical experiment, 2,3- dicyanonaphthalene-l,4-diol(13) (1.0 g, 4.8 x lop3 mol), ethyl iodide (3.7 g, 2.4 x lop2 mol), and anhydrous potassium carbonate (3 g) in anhydrous acetone (75 ml) were heated under reflux for 60 h. The mixture was filtered whilst hot and the residue washed with warm acetone (2 x 50 ml). The washings were combined with the reaction solution and the whole evaporated to dryness. The residue was recrystallised from acetone to afford 1,4-diethoxynaphthafene-2,3-dicarbonitrile (lob) (0.25 g, 40), m.p. 169--171 "C as light tan needles. Table 1 summarises yields and combustion analysis data for 20 compounds prepared by the above procedures.Two more derivatives, 4,5-dichloro-3,6-dipentyloxyphthalonitrile (9e) (58), m.p. 4-8 "C, v,,,.(thin film) 3 050-2 800 (CH), 2 230 (C-N), 1 240 and 1050 cm-' (C-0-C), and 3,6-dioctyl-oxyphthalonitrile (llh) (51), m.p. 147 "C, v,,,,(thin film) 3 075 (CH aromatic), 2 920 (CH aliphatic), 2 220 (C=N), 1 275 and 1050 cm-' (C-0-C), were used in the next step without purification. Metal-free Phthalocyanine and Naphthalocyanine Derivatives (Tables 2 and 3).-Procedure (c). In a typical experiment, a modification of the method of Witkiewicz et al., lithium metal (0.75 g) was added to a refluxing solution of 3,6-diethoxy- phthalonitrile (1.0 g, 4.6 x mol) in pentanol(10 ml) under a nitrogen atmosphere.The reaction solution was maintained at reflux for 0.75 g, cooled, and stirred into glacial acetic acid (100 ml). After 0.25 h, the bulk of the solvent was removed and the green residue dissolved in dichloromethane (50 ml). The solution was washed with 10 hydrochloric acid (100 ml) and brine (100 ml) and the organic phase separated, dried (MgSO,), and evaporated. The residue was chromatographed (silica gel, CH,Cl, and ether as eluants) and the green fraction recrystal- lised from a slowly evaporating solution in CH,Cl,-pyridine (95 :5) to yield metal-free 1,4,8,11,15,18,22,25-octaethoxy-phthalocyanine (0.2 g, 2073, m.p. 300 "C. Procedure (d). In a modification of the above procedure, a solution of 1.5~ butyl-lithium (0.64 g, 0.01 mol) in THF was added under nitrogen to a stirred solution of octanol (5 g, 38 mmol) at room temperature.The temperature was raised to 145-1 50 "C and 1,4-dioctyloxynaphthalene-2,3-dicarbonitrile (0.5 g, 1.15 x lop3mol) was added. The reaction was heated for a further 1 h, cooled and worked-up as above to yield metal-free 1,6,10,15,19,24,28,33-octaoctyfoxynaphthafocyanine(0.075 g, 15), m.p. 148 "C. Metal phthalocyanine and naphthalocyanine derivatives (Table 4). Procedure (e). In a typical reaction copper(1r) acetate monohydrate (0.75 g, 3.7 x mol) was added to a refluxing solution of metal-free 1,4,8,11,15,18,22,25-octapropyloxy-phthalocyanine (0.1 g, 1.02 x mol) in butan-1-01 (5 ml). The solution was maintained at reflux for 0.5 g, cooled, and chromatographed (silica gel, CH,Cl, and ether as eluants). The green-blue fraction eluted first was crystallised from a slowly evaporating solution in CH,Cl,-pyridine to afford the copper analogue (0.086 g, 81), m.p.300 "C. Spectroscopy.-U.v.-visible spectra were measured for solutions in spectroscopic grade toluene or Aristar grade J. CHEM. SOC. PERKIN TRANS. I 1988 chloroform using either a Pye-Unicam SP8-200 or a Cary 17D UV-Visible spectrometer. Fluorescence spectra of compounds (la) and (3d) were measured using a home-built spectro- fluorimeter described elsewhere l4 and corrected by standard procedures. The fluorescence spectrum of compound (5e) was measured at the Royal Institution, London using a Perkin- Elmer MPF4 fluorescence spectrometer fitted with a Hitachi R446 photo-multiplier. The spectrum was uncorrected.Solubility of Pcs in Liquid Crystals.-The dye (2-10 mg) was added to the liquid crystal E7 (200-250 mg) (B.D.H. Ltd. Poole) and the mixture stirred (Denley Spiramix) at room temperature for a continuous period of at least 2 weeks. An excess of the dye was maintained during this period. The resultant mixture was filtered (Millipore, pore size 0.2 pm) and a known weight of the filtrate (10-20 mg) was dissolved in either Spectrosol grade chloroform or Aristar grade dichloromethane (10-25 ml). The absorption spectra of the solution and that of a standard solution (ca. lop6molar) of the dye in Spectroscol grade chloroform were recorded (Perkin-Elmer Lambda 9 UV/Vis./Near TR spectrophotometer).The absorbance of the solutions at their wavelength maxima were used to calculate the solubility of the dye in the liquid crystal E7 at room temperature. Acknowledgements We thank the S.E.R.C. for financial support and for a CASE award with RSRE-Malvern (S. D. H.). We also thank Mr. Russell Svenson, Royal Institution, London, for measuring the emission spectrum of compound (5). References 1 M. Whalley, J. Chem. Soc., 1961, 866. 2 e.g. (a) S. A. Mikhalenko and E. A. Luk'yanets, Zh. Obshch. Khim., 1969, 39, 2129; (b) S. A. Mikhalenko, E. A. Korobkova, and E. A. Luk'yanets, ibid., 1970, 40, 400; (c) P. J. Duggan and G. P. Francis, Eur. Pat. Appl. EP 1565,780 (25 Sept., 1985, Chem. Abstr., 1986, 105, 70242r). 3 S. A. Mikhalenko and E. A. Luk'yanets, Zh. Obshch. Khim., 1969,39, 2554. 4 N. B. McKeown, Ph.D. Thesis, University of East Anglia, Norwich, 1987. 5 Z. Witkiewicz, R. Dabrowski, and W. Waclawek, Material Science, 1978, 11, 39. 6 K. Wallenfels, G. Bachmann, D. Hofmann, and R. Kern, Tetrahedron, 1965, 21, 2239. 7 A. B. P. Lever, Ado. Inorg. Chem. Radiochem., 1965, 7, 27. 8 L. E. Lyons, J. R. Walsh, and J. W. White, J. Chem. Soc., 1960, 167. 9 A. R. Koray, V. Ahsen, and 0. Bekoroglu, J. Chem. SOC., Chem. Commun., 1986, 932. 10 E. A. Cuellar and T. J. Marks, Inorg. Chem., 1981, 20, 3766. 11 P. J. Duggan and G. P. Francis, Eur. Pat. Appl., EP 155 780,25 Sept. 1985 (Chem. Abstr., 105, 70242r). 12 P. W. D. Mitchell, Can. J. Chem., 1973, 41, 550. 13 G. A. Reynolds and J. A. Van Allen, J. Org. Chem., 1964, 29, 3591. 14 M. J. Cook, A. P. Lewis, G. S. G. McAuliffe, V. Skarda, A. J. Thomson, J. L. Glasper, and D. J. Robbins, J. Chem. Soc., Perkin Trans. 2, 1984, 1293. Received 18th January 1988; Paper 8/00194D