TUNING OF THE EXCITED-STATE LIFETIME BY CONTROL OF THE STRUCTURAL RELAXATION IN OLIGOTHIOPHENES

The optical excitations of quaterthiophenes in which one (or two) inte r-ring torsional angles have been blocked by chemical bridging have be en studied with various cw and time-resolved spectroscopic techniques. The suppression of inter-ring torsion modifies the deactivation path of the excited start: leading to ii reduction of nonradiative decay. T his implies an increase of the lifetime of the singlet excited state a nd therefore of the photoluminescence quantum yield for the compounds with reduced conformational mobility. It is found that tripler transie nt absorption spectra are strongly affected by central inter-ring brid ging, showing features which are tentatively related to different conf ormers. [S0163-1829(98)03338-4].