Time-resolved spectroscopic studies of laser induced processes on terthiophene in inorganic-organic hybrid polymer matrices Original Research Article

The transient spectral behavior of α-terthiophene (3T) in a TiO2SiO2 and a SiO2-inorganic-organic hybrid polymer matrix has been studied after excitation with 12 ps UV pulses at 349 nm. In both materials an excited state absorption from the S1 state has been observed. Two additional absorption bands observed in the TiO2SiO2 hybrid polymer film at 550 and 865 nm were assigned to 3T radical cation transitions. The absence of the radical cation absorptions in the SiO2-inorganic-organic hybrid polymer film indicates, that titanium is involved in the radical cation formation of 3T. The 3T lifetime of the S1 state has been determined to be 15 ps in the TiO2SiO2 hybrid polymer matrix (TSHP-matrix), 72 ps in the SiO2 hybrid polymer matrix (SHP-matrix), but 135 ps in dioxane solution. The decay of the radical cations exhibit a fast component (53 ps) and a long living component interpreted as a fast geminate recombination and a trapping process, respectively. The picosecond pump probe experiments show that the radical cation formation starts from higher vibronic levels of the S1 state and represents an effective competing pathway for the S1 depletion. The solute-like behavior of 3T molecules incorporated in the hybrid polymer matrices was proved by Raman and steady state absorption measurements.