Preparation of a Series of Oligo[thiophene-2,5-diyl]vinylenes

Ahstraft -Preparation of a series of oligo[thiophene-2.5-diyl]vinylenes(3) is reported.Compounds containing an even number of thiophene rings were synthesized by the carbonyl coupling of thiophenecarbaldehydes with a low-valent titanium reagent and those canying an odd number of thiophene rings by the coupling of thiophenecarbaldehydes with Wittig-Homer (Wittig) reagents.Uv-vis spectral feature of these compounds is also reported.The chemistry of thiophene oligomers has been attracting much attention because of their biological activities and as starting materials for building molecular electronic devices.'Recently, we have reported the preparation of a-type oligothiophenes (I)? and a,p-type oligothiophenes (2)3 and have been investigating the physico-chemical properties of these compounds to find their applications as molecular electronic devices."In this connection, we have now become interested in the preparation of a series of oligo[thiophene-2,5-diyllvinylenes (3) that have an extended conjugated system which is crucial for building molecular electronic devices.All of the double bonds of 3 must have E-geometry for attaining effective conjugation over the whole molecule.Prior to our synthetic study, Kossmehl et al. reported the preparation of some of these c0m~ounds.5We have adopted a different synthetic methodology to prepare a series of these compounds and obtained them satisfactorily in higher purity.