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

The transient spectral behavior of alpha-terthiophene (3T) in a TiO2-SiO2 and a SiO2-inorganic-organic hybrid polymer matrix has been studied after excitation with 12 Fs 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 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 S-1 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 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. (C) 1998 Elsevier Science B.V.