Measurement of thermal modulation of optical absorption in pump-probe spectroscopy of semiconducting polymers

We analyze the transient absorption spectra of regioregular poly(3-hexylthiophene) films and find substantial response due to heating of the sample by the picosecond pump-pulse. The increased transmission at the onset of the absorption spectrum, caused by thermal blueshifting of the absorption, produces responses that have often been misinterpreted as arising from electronic excited states. We demonstrate that the use of a high thermal conductivity substrate such as sapphire allows thermal effects to be conveniently separated from electronic excited states. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3595340]