Effect of thienyl groups on the photoisomerization and rotamerism of symmetric and asymmetric diaryl-ethenes and diaryl-butadienesElectronic supplementary information (ESI) available: (1) Calculated electronic spectra (transition energy and oscillator strength) and ground state total energy of the rotamers of the trans isomers; (2) Absorption and emission spectra. See http://www.rsc.org/suppdata/pp/b4/b408241a/.

Five symmetric (bis-substituted) and asymmetric (mono-substituted) analogues of E-stilbene and EE-1,4-diphenylbutadiene, where one or both the side aryls are 2'-thienyl or 3'-thienyl groups, have been studied by stationary and pulsed fluorimetric techniques, laser flash photolysis, conventional photochemical methods and theoretical calculations. The results obtained for these compounds and the comparison with those previously reported for three other compounds of the same series, allowed the effects of the position of the heteroatom and of the extension of the olefin chain on the excited state relaxation properties to be understood. The presence of one or two thienyl groups and their positional isomerism affect the spectral behaviour, the relaxation properties ( radiative/reactive competition), the photoisomerization mechanism (singlet/triplet) and the ground state rotamerism. For the dienes containing the 3'-thienyl substituent(s), two rotamers were evidenced whose radiative and photochemical properties were obtained by selective excitation.