Ultrafast Relaxation Dynamics of a Single-Crystal Polydiacetylene, PDA-DFMP

Abstract

Conjugated polymers, such as polydiacetylenes (PDAs), exhibit ultrafast photo-induced response times and large optical nonlinearities; consequently PDAs are attractive candidates for potential applications in nonlinear optical devices. Recently the ultrafast photoexcitation decay processes of several conjugated polymers have been investigated [1,2]. The ultrafast relaxation dynamics of these systems can be explained by the self-trapped exciton relaxation model [3]. By synthetically altering the sidegroups, R and R′, in the backbone structure _n the linear optical properties of PDAs such as the exciton transition energy can be modified. However, an understanding of how these ultrafast properties may vary with different chemical modifications of PDAs is still quite limited. In this work we report the first study of the ultrafast relaxation dynamics of a PDA that has sidegroups π-conjugated to the main chain. Femtosecond pump-probe time-resolved spectroscopy is employed to measure both the photo-induced spectral and temporal response of a single-crystal of PDA-DFMP, where R = R′ = 2,5-bis trifluoromethyl-phenyl.