Ultrafast Excited State Dynamics of a Fluorene Derivative Conjugated Polymer

A detailed photophysical study ofa polymer based on a fluorenederivative is performed through ultrafast nonlinear spectroscopy.The polymer chains are studied in solution, where absorption and emissionoccur from a disordered distribution of isolated chains, and in solidstate as a film, where interchain interactions promote efficient energytransfer. Coherent photoexcitation produces delocalized excitons,which relax and localize on the lowest energy chromophores on thepolymer chains on a 100 fs time scale. This is revealed by ultrafasttransient absorption spectral evolution, anisotropy relaxation, andexcited state specific high time resolution fluorescence spectroscopy.The photophysical behavior of the polymer in solution and as a filmis significantly different suggesting a near absence of self-collapsedchain conformations in solution. In the film, the excited state relaxesan order of magnitude faster when compared to solution, indicatingthat interchain interactions are strong, promoting efficient energytransfer. The time scales of exciton dynamics revealed in this studywill support further theoretical modeling of these polymer structuresand are useful for designing blends for use in optoelectronic andelectro-optical devices