Polydiphenylsilanes bearing photosensitive azocrown groups{ Liviu Sacarescu,* a Rodinel Ardeleanu, a Gabriela Sacarescu, a Mihaela Simionescu a and Nicolae Hurduc b Received (in Cambridge, UK) 6th October 2005, Accepted 8th December 2005 First published as an Advance Article on the web 6th January 2006 DOI: 10.1039/b514161c This work presents the synthesis and particularities of the reversible trans–cis UV light induced photoisomerization process of a polydiphenylsilane bearing (propyl-oxyphenylazo)- dibenzo-18-crown-6 side groups. Polysilanes possess unique optical and electronic properties due to the electronic structure of the s-electron conjugated polymer chain. Such special properties are not exhibited by crystalline Si 3D systems. 2 Over the past few years, an increasingly large number of papers described various methods of obtaining unusual polysilane structures with intriguing properties. 3 Such structures, like soluble quantum conductors (QWR) 1a,4 or polysilane–metal complexes 3a,5 find applications as organic semiconductors or NLO materials. This paper presents the synthesis of a new poly[diphenyl-co- methyl(propyl-oxyphenylazo-dibenzo-18-crown-6)]silane, PSADF. The azocrown side segments allow the trans–cis isomerization induced by irradiation with a specific UV wavelength and provide the polysilane with the electrochemical sensitivity of the crown ether units. The synthesis procedure starts from poly[diphenyl-co-methyl- (bromopropyl)]silane (PSBDF) which was obtained through the addition of allyl bromide to soluble poly[diphenyl-co- methyl(H)]silane with M w = 48 6 10 3 g mol 21 , M n = 40 6 10 3 g mol 21 (GPC analysis vs. polystyrene standards) and Ph 2 Si/Me(H)Si ratio of 3 : 1, in the presence of a catalytic amount of H 2 PtCl 6 ?6H 2 O (1% solution in isopropanol). 5c An addition yield of 91% in the bromopropyl groups was calculated using the 1 H NMR integral for the –SiCH 3 – signal and elemental analysis. At high temperature, in anhydrous solvent (DMF), PSBDF undergoes a modified Williamson reaction with (4-hydroxypheny- lazo)dibenzo-18-crown-6 in the presence of anhydrous K 2 CO 3 (Scheme 1). Poly[diphenyl-co-methyl(propyl-oxyphenylazo- dibenzo-18C6)] silane (PSADF) resulted as a brown solid (g = 63%) with M w = 87 6 10 3 g mol 21 , M n = 70 6 10 3 g mol 21 and mp = 232 uC. Unlike the bromopropyl-polysilane which has a low decomposition temperature, in this case the TGA analysis in air shows decomposition temperatures starting from 250–400 uC for the organosilicone backbone to 400–750 uC for the azo segment. It is known that the azobenzene derivatives undergo trans–cis photoisomerization in UV light with a temporary and local change of shape and polarity. 6 The process is reversible and reversion from cis to trans isomer state takes place thermally or by irradiation in the visible spectrum. 7 The photoisomerization of PSADF was performed by irradiation of the polymer solutions in DMSO with a 400 nm filtered UV light and recording the 480 nm absorption band corresponding to the n–p* transition of the azobenzene unit in cis conformation (Fig. 1). 8 This procedure was chosen because the azo group p2p* transitions overlap with the polysilane s2s* transitions. Another reason for choosing this procedure was to protect the polysilane chain against photodecomposition. UV irradiation caused an increase in the intensity of the 480 nm absorption band until a photostationary state was reached and about 65–70% of azobenzene segments were in cis configuration. The trans–cis photoisomerization data followed a first-order kinetics with a rate constant of 8.1 6 10 23 s 21 at 25 uC. The isomerization process was reversed by heating at moderate temperature (70 uC). Thermal recovery needed much longer a Institute of Macromolecular Chemistry ‘‘ Petru Poni’’, Aleea Gr. Ghica Voda 41A, Iasi, Romania. E-mail: livius@icmpp.ro; Fax: +40 232 211299; Tel: +40 232 217454 b Technical University ‘‘Gheorghe Asachi’’Supramolecular Chemistry & Molecular Modelling Dept., B-dul. D. Mangeron 71A, Iasi, Romania. E-mail: nhurduc@ch.tuiasi.ro; Fax: +40 232 271311; Tel: +40 232 271311 { Electronic supplementary information (ESI) available: Experimental details. See DOI: 10.1039/b514161c Scheme 1 Fig. 1 (a) UV spectrum of trans-PSADF; (b) change of the absorption spectra of DMSO solutions of PSADF during trans–cis photoisomeriza- tion recorded at 0, 5, 10, 15, 20, 25, 30 min and 25 uC; (c) increasing of 280 nm peak recorded during trans–cis photoisomerization of PSADF. COMMUNICATION www.rsc.org/chemcomm | ChemComm 788 | Chem. Commun., 2006, 788–789 This journal is ß The Royal Society of Chemistry 2006 Published on 06 January 2006. Downloaded by UNIVERSITY OF ALABAMA AT BIRMINGHAM on 27/10/2014 01:52:26. View Article Online / Journal Homepage / Table of Contents for this issue