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

Abstract

The transient spectral behavior of α-terthiophene (3T) in a TiO 2SiO 2 and a SiO 2-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 S 1 state has been observed. Two additional absorption bands observed in the TiO 2SiO 2 hybrid polymer film at 550 and 865 nm were assigned to 3T radical cation transitions. The absence of the radical cation absorptions in the SiO 2-inorganic-organic hybrid polymer film indicates, that titanium is involved in the radical cation formation of 3T. The 3T lifetime of the S 1 state has been determined to be 15 ps in the TiO 2SiO 2 hybrid polymer matrix (TSHP-matrix), 72 ps in the SiO 2 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 S 1 state and represents an effective competing pathway for the S 1 depletion. The solute-like behavior of 3T molecules incorporated in the hybrid polymer matrices was proved by Raman and steady state absorption measurements.