Femtosecond Time-Resolved Spectroscopic Studies on Thiophene Oligomers

Thiophene oligomers ( n T) with two to six units in solution are studied under pulse excitation (308 nm,350 fs) in the spectral range 430−830 nm. Transient absorption and induced fluorescence emerge within 1−2 ps. An “instant” absorption (A0), which shows a size dependent spectral structure superimposes the induced fluorescence during the first 500 fs. The fast kinetic processes of different n T are very similar during the first picosecond. They were interpreted as relaxation starting from the highest accessible electronic level down to the lowest excited-state S 1 of each oligomer.