Excited state dynamics of a conformationally disordered conjugated polymer: A comparison of solutions and film

We compare poly[2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylenevinylene] (MEH-PPV) solutions in chlorobenzene, toluene and tetrahydrofuran with a film of MEH-PPV spun cast from chlorobenzene solution using the three-pulse photon echo (3PEPS) experiment to examine the origins of line broadening in these systems which are obscured in spectral line shapes. We have simulated the 3PEPS data simultaneously with the absorption and fluorescence spectra to elucidate the timescales characteristic of relaxation processes. Simulations show a rapid localization of excitation in the initial ∼20 fs. The conformation of chains in solution and film dictates the Coulomic interaction between proximate subunits which in turn influences the extent of initial delocalization, chromophore size and energy transfer. We report an increased energy transfer efficiency in the films as compared to the solutions as evidenced by the decay of the peak shift to zero.