Resolving the radical cation formation from the lowest-excited singlet (S-1) state of terthiophene in a TiO2-SiO2 hybrid polymer matrix

Photoexcitation dynamics of terthiophene (3T) molecules incorporated in an organic-inorganic matrix containing titanium in the network are investigate d by polarized transient absorption with femtosecond time resolution. We ob served the decay of excited-state absorption of neutral 3T and simultaneous rise of 3T(-)(+.) radical cation absorption. The observed kinetics of elec tron transfer are independent of excess vibrational energy in the S-1 state , and can be described by a biexponential function with time constants of s imilar to 1 ps (for similar to 62% of the excited 3T molecules) and similar to 8 ps (for similar to 33%). The angle between the S-1 <-- S-0 absorption dipole moment of neutral 3T and the absorption dipole moment of the 3T(+.) radical cation is estimated to be similar to 30 degrees. About one-half of the generated charge pairs do not recombine within 0.5 ns, which is an att ractive feature for application in photovoltaic devices. (C) 1999 Elsevier Science B.V. All rights reserved.