Synthesis 13C NMR, lambda-max and MMP2 calculations of two 'tailor-made' alpha-conjugated hexamethylsexithiophenes

3, 3', 4", 3"', 4"", 3""' - and 4, 4', 3", 4"', 3"", 4""' - hexamethyl 2, 2':5', 2":5", 2"':5"', 2"":5"", 2""' sexithiophenes (I and II) have been prepared by nickel-phosphlne catalyzed Grignard coupling and their conformational properties investigated with the aid of 13C NMR spectra and MMP2 force field calculations. Owing to the presence of the substituents, the molecular skeletons are not planar and large blue shifts of the lambda-max are observed.