Abstract
We used fluorescence up-conversion technique to investigate a series of regioregular silylene-spaced alternating donor-acceptor copolymer (D1,3A)m. Here D and A denote 4,4□-divinylbiphenyl and 4,4□-divinylstilbene, respectively. Silylene group can prevent over-extended conjugation between the chromophores in the polymer so that the photophysical properties of the polymer can be tuned. The alkyl substituents on silicon render the polymer more soluble in organic solvents. With 266 nm excitation the fluorescence curves of donor monomer exhibit a rise time constant □100 fs, and two decay time constants, 7-65 ps and □1 ns. We attribute the former rise to internal conversion from Sn to the S1 state, and the latter decay to geometric relaxation and the lifetime of the S1 state. Only the tens of picosecond decay shows a dependence on the solvent viscosity, indicating that the torsional motion dominates the relaxation. Upon excitation of donor moieties in (D3A)m, the fluorescence is almost exclusively from the acceptor regardless of the excitation wavelength, indicating an efficient energy transfer between donor and acceptor. Femtosecond time-resolved fluorescence indicates a rate (0.3 ps)-1 and (0.6 ps)-1 for energy transfer between S1 states of the donor and the acceptor is observed in (D3A)m and (DA)m, respectively. The observed energy transfer rate in (D3A)m is well described by the F□rster theory, indicating that dipole–dipole interaction dominates the energy transfer process. The discrepancy between the energy transfer rates observed in (D3A)m and (DA)m implies the coupling between donor and acceptor is different. Finally, intramolecular aggregation is observed in both (D3A)m and (DA)m, with rates (5 ps)-1 and (7 ps)-1 respectively, of energy transfer to the aggregates. The experimental results show that silylene-spaced copolymers are promising in the application of light-harvesting materials from the ease of preparation and the ultrarapid rate of energy transfer.