Excitation energy migration in uniaxially oriented polymer films

Multistep nonradiative excitation energy transport is for the first time studied in uniaxially stretched polymer films. Concentration depolarization studies performed for 3,3′-diethylthiacarbocyanine iodide (DTCI) for stretched (system I) and unstretched (system II) polyvinyl alcohol films (PVA) yield extremely different results. As expected, disordered system II exhibits strong concentration depolarization due to energy migration between identical fluorophores. However, for stretched films, concentration depolarization effect is much weaker and it occurs at higher dye concentrations compared to system II. This fact is mostly due to strongly modified angular distribution of dipole moments of molecules taking part in the excitation energy migration.