| Abstract
| - The transport and relaxation dynamics of singlet excitons of rodlike [tetramethoxytetrakis(octyloxy)phthalocyaninato]polysiloxane (PcPSi) in tetrahydrofuran solution were investigated on the femtosecond scaleby transient absorption spectroscopy. Singlet excitons are generated upon excitation into the ground-stateabsorption at 555 nm using laser pulses of 120 fs duration with different intensities. Transient absorptionspectra were recorded at variable delays using a white-light continuum probe pulse. Both photoinducedbleaching and transient absorption show nonexponential decay dynamics with a pronounced dependence onthe excitation energy density. The analysis of the decay dynamics of the photoinduced bleaching and transientabsorption at lower excitation densities is made by including, in addition to the monomolecular, exponentialdecay with lifetime τ, a time-dependent bimolecular exciton−exciton annihilation rate constant γt-1/2,characteristic of one-dimensional diffusive exciton transport. At high excitation densities, the observed decaystrongly deviates from this behavior, as a new relaxation channel is opened, which is attributed to short-lived, charge-separated states.
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