Exciton diffusion in ladder-type methyl-substituted polyparaphenylene film and solution was investigated by means of femtosecond pump-probe spectroscopy using a combined approach, analyzing exciton-exciton annihilation, and transient absorption depolarization properties. We show that the different views on the exciton dynamics offered by anisotropy decay and annihilation are required in order to obtain a correct picture of the energy transfer dynamics. Comparison of the exciton diffusion coefficient and exciton diffusion radius obtained for polymer film with the two techniques reveals that there is substantial short-range order in the film. Also in isolated chains there is considerable amount of order, as revealed from only partial anisotropy decay, which shows that only a small fraction of the excitons move to differently oriented polymer segments. It is further concluded that interchain energy transfer is faster than intrachain transfer, mainly as a result of shorter interchain distances between chromophoric units.

Nonlinear exciton relaxation processes, exciton-exciton annihilation, and amplified spontaneous emission were investigated in thin films of ladder-type poly-(para-phenylene) under excitation by femtosecond light pulses. Both processes become apparent at similar excitation intensities, however their properties are very different. They cause different exciton relaxation kinetics and their intensity dependences are different.

No abstract