TRIALKOXYSILYL MONOTHIOPHENE, BITHIOPHENE, AND TERTHIOPHENE AS MOLECULAR PRECURSORS OF HYBRID ORGANIC-INORGANIC MATERIALS

Silica gel containing thiophene units have been obtained from molecular organosilicon precursors, and the properties associated to the electron rich thiophene moieties have been explored. The sol-gel polymerization of 2,5-bis(trimethoxysilyl)mono-, bi-, and terthiophene quantitatively led to thiophenylene bridged silsesquioxane network: [O1.5Si-(C4H2S)p-SiO1.5]n (p = 1-3). The derived xerogels were characterized by IR and C-13 and Si-29 CP MAS NMR spectroscopies. The major environment of the Si atom corresponded to a T2:CSi(OR)(OSi)2 substructure. The gels are microporous with N2 BET surface area up to 685 m2g-1. A charge-transfer complex containing gel was also obtained upon cohydrolysis and condensation of Si-(OMe)4 with 5,5''-bis(trimethoxysilyl)terthiophene/TCNQ charge-transfer (CT) complex. The CT units and the siloxane network in the hybrid material were respectively characterized in the electronic spectrum exhibiting an absorption band of the [TCNQ-] radical anion and in the Si-29 CP MAS NMR spectrum showing CSiO3 and SiO4 substructures. The electrochemical oxidation of thiophenylene-bridged gels led to the polymerization of the thiophene units. Si-29 CP MAS NMR of the oxidized materials revealed the cleavage of the Si-C bond in the solid. The formation of polythiophene within the inorganic matrix was established on the basis of Raman spectroscopy. It was further confirmed by the isolation of some soluble oligomers upon oxidation of a related monosilylthiophene gel. The polymerization, which occurred in the solid, gave a composite material containing polythiophene chains and a silica network.