Ultrafast intramolecular energy transfer in single conjugated polymer chains probed by polarized single chromophore spectroscopy

Single molecule spectroscopy of rigid-rod ladder-type conjugated polymers reveals individual chromophore units on a polymer chain, exhibiting fluorescence linewidths of less than 1 nm. Whereas the fluorescence from a single chromophore is fully linearly polarized at low temperatures, a number of excitation pathways and polarizations exist due to rapid intramolecular energy transfer to the emitting site. We propose that the slightly branched structure of the polymer results in neighboring molecular sites with orthogonal dipole orientations, enabling rapid polarization rotation. We demonstrate linearly polarized emission, which is independent of the excitation plane of polarization and may form the basis for molecular optical logic operations.