Intrachain photoluminescence dynamics of a long oligothiophene at room temperature

The temperature dependence of the photoluminescence (PL) and absorption spectra of the 16-mer oligothiophene (16 T) extremely diluted in polypropylene (PP) has been investigated to clarify the PL dynamics at room temperature of quasi-isolated conjugated polymers. Both of the PL and absorption spectra of 16 T in PP are found to blueshift with increasing temperature, due to the thermal conformational change. The Stokes shift estimated by the difference of the 0–0 peak between the absorption and PL spectra is shown to increase with temperature. It is found that the time-resolved PL spectra at room temperature of 16 T in PP exhibit a larger transient redshift than those at 4 K. The increase of the Stokes shift is thus concluded to result from the enhanced transient redshift due to the conformational change. The magnitude of the Stokes shift increasing with temperature is shown to be reduced in the case of 12-mer oligothiophene diluted in PP compared to that of 16 T in PP. This leads us to conclude that the thermal inhomogeneity increases with elongating the chain length. It is also shown that the exciton migration occurs in the time scale of several hundreds of picoseconds and competes with decay of emission.