ELSEVIER Synthetic Metals 102 (1999) 1.527-1528 A Series of Novel Liquid Crystalline Octakis(alkylthio)-substituted Phthalocyanines A. Lux ‘, G.G. Rozenberg ‘, K. Petritsch h, SC. Moratti ‘, A.B. Holmes ‘,* , R.H. Friend h a Melville Luborutoryfiw Polymer Synthesis, University cfCumbrid~e, New Museums Site, Pembroke Street, Cur&ridge CB2 3RA, U.K. b Depurtment of’Physics, Cuvendish L.uborurory, Mudinxley Roud, Cambridge CB2 OHE, U.K. Abstract Liquid crystalline phthalocyanines (PC’S) are promising materials for opto-electronic applications (e.g. solar cells, electrophotography) due to their high absorption coefficients in the long wavelength region of the optical spectrum and high charge carrier mobilities in the columnar mesophase. We report here the synthesis and properties, in particular the thermotropic phase behaviour, of a series of new octakis(alkylthio)-substituted Pc’s. Keywords: Heterocycle synthesis, Organic semiconductors based on conjugated molecules, Liquid crystalline phase transitions 1. Introduction Phthalocyanines (PC’S) and in particular their discotic liquid crystalline derivatives have attracted our attention for use in photovoltaic cells. Their extended two-dimensional n-conju- gated electron systems make them very effective absorbers in the lower energy visible light region which is reflected in numerous applications in the field of opto-electronic devices [I]. By attaching eight long side-chains PC’S can not only be orientated in highly ordered columnar mesophases of high charge carrier mobility [2], but are also solution-processible simplifying device manufacture. We report here on the synthesis of novel octakis(alkylthio)- substituted PC’S in comparison with previously reported literature [3, 41 and investigate for the first time how alkylthio- substituents affect the liquid crystalline properties of octa- substituted PC’s The thermal stability as well as absorption and luminescence properties were also investigated. 2. Results and Discussion The synthetic route used is an adopted literature procedure [3], starting from 4,5-dichlorophthalic acid 1 (Scheme 1). However, conversion of 1,2-dichloro-4&dicyanobenzene 2 into the 1,2-dialkylthio-4,.5-dicyanobenzenes 3 was performed under milder conditions, giving 3 in better yields of up to 84%. Synthesis of metal-free PC’S (4a-d) and of their copper @a-d) and cobalt complexes (6a-d) was accomplished according to literature procedures [4, 51 by thermal treatment of 3 with DBU or with the corresponding anhydrous metal salts. All materials were purified carefully by column chromatography and the structures established by IR, NMR and mass spectroscopy. The thermotropic phase behaviour of the PC’S was investigated by differential scanning calorimetry (DSC) and polarizing microscopy. The transition temperatures observed upon heating and cooling are summarised in Table 1. All mesophases were found to be very viscous at lower temperatures. * corresponding nuthor Scheme 1. Synthesis of PC’S with the central atoms H, Cu, Co 0 Cl 1. AsO, reflux, 97% 2. HCON& reflux, 85% RSH, K&O> Cl 3. NH,. r.t., 93% --GE--+ 4. SOCI,, r.t., 71% 0 ;gxn,r.t. 00 2 1 RS 3 RS SR 4 4a: R = n-CbHi3; M = 2H; 32% n: SC:R = n-CizH2s; M = Cu; 41% 4b: R = II-CxHi7; M = 2H; 18% 5d: R = n-CigHj7; M = Cu; 65% 4c: R = n-Ci2H2s; M = 2H; 32% 6a: R = n-CbHi3; M = Co; 27% n 4d: R = n-CixH17; M = 2H; 15% 6b: R = n-&HIT; M = Co; 35% 5a: R = n-CeHix; M = Cu; 58% XI 6c: R = n-CizHzs; M = Co; 26% 5b: R = n-CxHi7; M = Cu; 75% 6d: R = n-CixH3-r; M = Co; 10% n reported in [4] Table 1. Phase transition temperatures (“C) of PC’S PC IK 1 ID 1 II 4c (H2PcSC12) I. I20 (4) I. 1 292 (288) I. ( ) indicate transitions upon cooling, heating/cooling rate IOWmin As a consequence, not all DSC peaks could be confirmed optically. Transition temperatures of the octakis(alkylthio)- substituted PC’S investigated here are generally lower in comparison with those of their oxygen analogues [5], but also decrease with increasing chain length [6]. 0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)01 149-7