Conformational equilibria in EE-1,3-di-(3′-thienylethenyl)benzene: One-way adiabatic interconversion of rotamers in S1 and their excited state properties

The present results lead to a complete and quantitative description of the conformational equilibrium including the radiative and radiationless relaxation rate parameters of the lowest excited states of the two rotamers. A simultaneous singlet and triplet mechanism for the geometrical photoisomerization, with an involvement of the former above room temperature only, seems to reasonably account for the experimental results. The role played by the rotamers in the photoreactive behaviour of (3TE)2B is also discussed.