Observation of multiple step de-excitation in luminescent single conjugated polymers

The fluorescence intensity fluctuation and polarization modulation of spin-cast single fluorescent conjugated polymers of 2,5-dioctyloxy p-phenylene vinylene (DOO-PPV) with length of the order of the persistence length have been studied. The results indicate that this type of polymer behaves like a collection of semi-independent excitons, with dipoles aligned predominately in the same direction. This suggests that this type of polymer can be considered as a linearly extended rigid structure (i.e., a straight rod). The fluorescent transient exhibits a multiple-step-like behavior with the count rate at each step being a multiple of a common step-size. The fluorescence variation follows the excitation polarization with a DC background observable in some molecules. This DC background indicates that the chromophores in some polymers are not aligned in the same direction. Variations in the Huang–Rhys factor at a single polymer level are also observed.