Picosecond spectroscopy and hyperlinear photoluminescence in poly(para-phenylene)-type ladder polymers

In our investigations of the photoluminescence in poly-(para-phenylene)-type ladder-polymer films a highly nonlinear dependence of the emission spectra is observable at elevated excitation densities. A spectral redistribution results in the hyperlinear increase of emission efficiency in the blue region, as the vibronic 0-1 transition (Formula presented) becomes the most predominant radiative relaxation. The detailed study of temporal decay and spectral evolution of luminescence provided by streak camera measurements performed in the temperature range (Formula presented) reveals the spectrum being composed by the contributions of two different emitting species, namely, (Formula presented)-singlet states and aggregates. The material is found to be photochemically stable and luminescence does not seem to be limited by saturation effects even under high-excitation conditions, which is essential for laser application.