Aggregation and excitation trapping of 3,3′-diethyl-9-methylthiacarbocyanine iodide in disordered and uniaxially oriented polymer films

Photophysical properties of 3,3′-diethyl-9-methylthiacarbocyanine iodide (MDTCI) in disordered and uniaxially stretched poly(vinyl alcohol) films (PVA) are reported at high dye concentration. Ground-state formation of fluorescent MDTCI aggregates at high concentration was observed in unstretched and stretched PVA films using steady-state and time-resolved spectroscopic methods. It was found that fluorescence of MDTCI aggregates is almost totally depolarized in disordered matrix, but it remains partly polarized in the stretched PVA film despite energy transfer from monomers. The differences between spectral properties of aggregates in both matrices may result from partial orientation of aggregate transition moment and its immobilization in polymer cage.