Charge and Energy Transfer Dynamics in Dimethylsilylene-Spaced Aminostyrene Stilbene Monomer Using Time-Resolved Techniques.

We used transient absorption and time-correlated single photon counting (TCSPC) techniques to investigate the charge transfer reaction in monosilylene-spaced aminostyrene stilbene monomer. With 266 nm excitation, both stilbene (sti) and aminostyrene (ast) moieties were excited. In nonpolar solvents, the transient absorption band centered at 600 nm appeared promptly and is assigned to the excited state of sti*; this state relaxes at time constant 1.2-1.4 ps and is explained to proceed energy transfer to ast 1ππ*. The second transient band at 460 nm is assigned to absorption of ast 2ππ*; this state accessed from direct excitation has a lifetime 65 ps. This agrees with the observation of 85-89 ps emission decay from the TCSPC measurements. In polar solvent, an excited absorption band centered at 530 nm appeared with a rise time constant 0.2-0.6 ps. This band is assigned to the charge transfer state. This charge transfer process occurs as the acceptor fluorophore (sti) is excited and the electron moves from the occupied π orbital of donor ast to sti* forming ast+sti-. This rise time corresponds to the combined processes of charge and energy transfers. The second rise in this charge-transfer state at time constant 0.74-1.5 ps is observed and assigned to occur from electron hopping from ast 2π* orbital to sti π*. The third time constant 18-31 ps is observed and is attributed to conversion of anti to syn form in the charge-transfer state because the syn form is more polar and further stabilized in polar environment. A rapid charge transfer process in monosilylene-spaced system although two Si-C single bonds are used as spacer is possibly because of the short distance of the ast and the sti conjugated systems, resulting in π orbital overlap between donor and acceptor.