Picosecond excitation energy relaxation processes in a ladder-type π-conjugated polymer

We studied the relaxation dynamics of excitations in the lowest electronically excited singlet state in a ladder-type π-conjugated polymer employing picosecond time-resolved spectroscopy with high spectral resolution. At 1.5 K both the decay dynamics and the rising component of the fluorescence transients from the low-energy tail of the distribution of excited states show a strong dependence on time and on the precise emission wavelength. At room temperature, in contrast, such dependencies are not observed. Finally, the data allow us to retrieve the radiative lifetime of the excited states both at 1.5 K and 296 K.