Low-Temperature Transient Optical Spectroscopy of Polydiacetylene DCHD: Evidence for a Distribution of Side Group Orientations

We report on the transient optical response of the polydiacetylene DCHD at low temperature. Ultrafast pump-probe spectroscopic measurements reveal that excitation of the polymer N-methyl carbazolyl side group results in instantaneous (<10 ps) excitation transfer to the polymer backbone at 10 K. The slow population recovery signal seen subsequent to excitation transfer to the polymer backbone exhibits an excitation energy dependence that is indicative of the existence of multiple conformers. The energy barrier between these conformers is inferred to be <0.5 kcal/mol.