The synthesis and characterization of novel mesomorphic octa- and tetra-alkylthio-substituted lead phthalocyanines and their films Devrim Atilla a , Ays ¸ e Gül Gürek a , Tamara V. Basova b, * , Vitaly G. Kiselev c, d , Aseel Hassan e , Liliya A. Sheludyakova b , Vefa Ahsen a, f a Gebze Institute of Technology, Department of Chemistry, P.O. Box: 141, 41400, Gebze, Kocaeli, Turkey b Nikolaev Institute of Inorganic Chemistry, SB RAS, 3 Lavrentiev Ave., Novosibirsk 630090, Russia c Institute of Chemical Kinetics and Combustion SB RAS, 3 Institutskaya Str., Novosibirsk 630090, Russia d Novosibirsk State University, 2 Pirogova Str., Novosibirsk 630090, Russia e Faculty of Arts, Computing, Engineering and Sciences, Sheffield Hallam University, Furnival Building, 153 Arundel Street, Sheffield S1 2NU, United Kingdom f TUBITAK-Marmara Research Center, Materials Institute, P.O. Box: 21, 41470, Gebze, Kocaeli, Turkey article info Article history: Received 19 May 2010 Received in revised form 12 July 2010 Accepted 16 July 2010 Available online 27 July 2010 Keywords: Lead phthalocyanines Liquid crystals IR spectroscopy Thin films abstract Two novel mesomorphic octakis and tetrakis (alkylthio)-substituted phthalocyanines of Pb(II) were synthesized and characterized using NMR, UVeVis, FT-IR and mass-spectrometry. The mesogenic properties of these new materials forming columnar-hexagonal mesophases were studied by differential scanning calorimetry, optical microscopy and X-ray diffraction. Visible absorption spectroscopy provided evidence of thermally induced molecular reorganization in films. IR spectroscopy and density functional theory calculations were used to study the preferential orientation of molecules relative to the substrate surface. The intense IR bands in the spectra of the lead phthalocyanines were assigned with the aid of quantum chemical computations. The observed increase in the intensity of the out-of-plane modes in the IR spectra correlate with an average preferential edge-on orientation of the molecules on the substrate surface in the film. The current-voltage characteristics of films before and after thermal treatment were also measured. The results confirmed the film ordering proposed on the basis of the IR and DFT studies. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Metal phthalocyanines (MPcs) are highly stable organic semi- conductors with a broad range of applications, such as light emitting diodes, solar cells, gas sensors, thin film transistors, and even single molecule devices [1]. Among the various MPcs, lead (Pb(II)) phtha- locyanines are of particular interest due to their promising sensor [2,3] and electrical switching properties [4e6]. While an unsub- stituted PbPc compound has attracted attention for a long time [7e13], only a few substituted PbPcs have been synthesized and characterized. Among the examples of those PbPc derivatives are the non-peripheral 1,4,8,11,15,18,22,25-octakis(hexylsulfanyl)Pc [14], non-peripheral tetraalkoxy-[15], tetra- and octa-diethoxymalonyle [16], cumylphenoxy- [17], tetranitro- [18], tetraamino- [19], and tetra-tert-butyl [20] derivatives. The structure of single crystals of Pb[Pc(SC 6 H 13 ) 8 ] and Pb[Pc(OC 5 H 11 ) 4 ] with substituents in non- peripheral positions were characterized by X-ray diffraction [14,15]. Non-linear optical properties of tetra-tert-butylnaphthalocyanine lead were also studied [20]. Density functional theory (DFT) calcu- lations were applied to obtain molecular structures, HOMOeLUMO energy gaps, atomic charges, vibrational and UVevis spectra of unsubstituted PbPc [21e23] and of some substituted PbPcR 8 compounds (R ¼ F, Cl, Br, H, eCH 3 , eC 2 H 5 , eC 3 H 7 ) [21], Pb[Pc (OC 2 H 5 ) 4 ] [23], and Pb[Pc(OC 5 H 11 ) 4 ] [23]. However, to our knowl- edge, no assignment of the IR bands in the spectra of substituted PbPcs has been made so far. A very promising and fascinating class of PbPc compounds is mesomorphic lead phthalocyanines. The first successful synthesis of such species was reported in 1987 [24,25]. Simon et al. [24] showed that alkoxymethyl substituted phthalocyaninato lead(II) complexes (PbPcR 8 ,R ¼ eCH 2 OC n H 2nþ1 ; n ¼ 8, 12) formed a hexagonal columnar mesophase which was stable at room temperature. Ford et al. [26] subsequently found that octa-(2-ethylhexyloxy) lead phthalocyanine exists in a mesophase in the temperature range from 100  C to þ200  C. Compounds with eCH 2 OR and eCH 2 CH 2 OR side chains turned out to be columnar liquid crystals with no detectable order within the columns [24,26]. An intra- molecular antiferroelectric coupling of the molecules along the * Corresponding author. Tel.: þ7 383 330 28 14; fax: þ7 383 330 94 89. E-mail address: basova@niic.nsc.ru (T.V. Basova). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig 0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2010.07.007 Dyes and Pigments 88 (2011) 280e289