Ultrafast Energy Transfer in Divinylbiphenyl and Divinylstilbene Copolymers Bridged by Silylene

The energy-transfer properties of a regioregular silylene-spaced alternating donor–acceptor copolymer [(donor)₃-SiMe₂–acceptor-SiMe₂]_<i>m</i> (denoted <b>(D</b>_<b>3</b><b>A)</b>_{<i><b>m</b></i>}) are determined with time-resolved spectroscopy; 4,4′-divinylbiphenyl serves as the donor and 4,4′-divinylstilbene as the acceptor. With excitation at wavelength 266 nm, fluorescence up-conversion curves at various detection wavelengths are measured. The observed decay of donor emission at a time constant 0.3 ps and the emission of the acceptor have a corresponding fast rise and a slower second rise at ∼2 ps. In the tail of fluorescence emission, the varied slow decay components (2–7 ps) on the donor and rise on the acceptor are observed and assigned to intrachain aggregates. With the Coulomb coupling which is beyond the multipole approximation, the Fermi golden rule rates of energy transfer are calculated between adjacent monomers and between the <b>D</b>_<b>2</b> exciton and <b>A</b>. In all <b>D</b>_<b>2</b><b>A</b> and <b>D</b>_<b>3</b><b>A</b> conformers calculated, we found that the coupling strengths of <b>D</b>–<b>A</b> and <b>D</b>–<b>D</b> are similar, but the coupling of exciton state <b>D</b>_<b>2</b> to the acceptor is about a factor of 1.25–1.72 weaker. According to the experimental data and the calculated results, we propose that the transfer between adjacent donors is ultrafast, so the excited donor has an energy transfer reaching the acceptor at a rate of ∼(0.6 ps)⁻¹ and transports via either direction to extend a final rate of (0.3 ps)⁻¹. According to the calculated ratios of coupling strength, the second rise component, 1–2 ps, is assigned to the transfer between the <b>D</b>_<b>2</b> exciton state and the acceptor