Tuning of the excited-state lifetime by control of the structural relaxation in oligothiophenes

The optical excitations of quaterthiophenes in which one (or two) inter-ring torsional angles have been blocked by chemical bridging have been studied with various cw and time-resolved spectroscopic techniques. The suppression of inter-ring torsion modifies the deactivation path of the excited state leading to a reduction of nonradiative decay. This implies an increase of the lifetime of the singlet excited state and therefore of the photoluminescence quantum yield for the compounds with reduced conformational mobility. It is found that triplet transient absorption spectra are strongly affected by central inter-ring bridging, showing features which are tentatively related to different conformers.