Exciton localization in thin polymer films probed by selective fluorescence spectroscopy

We performed selective laser excitation of fluorescence of thin films of poly(p-phenylene) (PPP) at room and liquid helium temperatures. Monochromatic laser excitation becomes selective upon excitation below a threshold frequency of 22 400 cm(-1) in the low-energy tail of the fluorescence excitation band, 2200 cm(-1) below the maximum of the excitation spectrum. The experimental results are interpreted on the basis of model calculations.