Heterogeneous energy landscapes of individual luminescent conjugated polymers

The energy landscape of single, isolated, short- and long-chain luminescent conjugated polymers was studied by photobleaching spectral shift analysis and interphoton time measurements. It has been found that the energy landscape of a polymer is dependent on both the conjugation length distribution as well as the arrangement of these conjugated segments. Energy funnels responsible for abrupt drops in the photoluminescence time trace intensity are found to be wide (in terms of the number of absorbing segments feeding energy into them) rather than deep (in terms of energy relative to the other emission sites in the polymer). Experimental results indicate that the energy landscape is influenced, but not dictated, by the solvent polarity. Moreover, it was observed that spectral blueshifts do not always accompany the quenching of a funnel, pointing to the existence of multiple independent regions of approximately the same energy distribution within an individual polymer.