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 DCH D at low temperature. Ultrafast pump-probe spectroscopic measurements reveal that excitation of the polymer N-methyl carbazolyl side group r esults in instantaneous (<10 ps) excitation transfer to the polymer ba ckbone at 10 K. The slow population recovery signal seen subsequent to excitation transfer to the polymer backbone exhibits an excitation en ergy dependence that is indicative of the existence of multiple confor mers. The energy barrier between these conformers is inferred to be <0 .5 kcal/mol.