Energy transfer between unlike fluorophores in uniaxially oriented polymer films monitored by time-resolved and steady-state emission anisotropy

Excitation energy transfer is studied for 3,3′-diethylthiacyanine iodide (DTTHCI, donor) and rhodamine 6G (R6G, acceptor) (system I) and 3,3′-diethyloxacarbocyanine iodide (DTCI, acceptor) (system II) in uniaxially stretched and unstretched polyvinyl alcohol films (PVA). Both systems differ strongly in the orientation degree of acceptor transition moments in the stretched polymeric matrix. As a result of weak orientation of R6G in PVA stretched matrix, strong acceptor depolarization of fluorescence upon donor excitation was observed for system I despite ordering the PVA matrix. However, for system II the transition moments of both DTTHCI and DTCI are correlated and orientate strongly along the direction of stretching resulting in the preservation of acceptor emission anisotropy upon steady-state and pulse excitation.