Bimodal inhomogeneity in conjugated polymer spectroscopy: Experimental tests of a two conformation model

The photophysics of conjugated polymer films can be accounted for using a model where chromophores assume only two distinct spectroscopic behaviors. We report two types of experiments on MEH-PPV that support this picture, showing that these sets of chromophores can be addressed independently and extracting their spectra. Chain segments in packed regions of the polymer have spectra with shape much like those in dilute solution but red shifted. Picosecond pump dump experiments show that isolated solution-like chromophoros are much more easily dumped than their aggregated analogs. We argue. however. that this is not primarily due to larger emission emission cross-section but rather due to the importance or rapid interchain processes in packed regions.