Photoinduced charge transfer mechanism in PPV [poly(p-phenylinevinylene)] polymer: role of iodide species

The photophysical and photochemical behavior of poly (p-phenylinevinylene (PPV) polymers in different solvents (toluene and Triton X-100) and in thin form [PPV/optical transparent electrode (OTE)] has been investigated by emission and transient absorption spectroscopies. The absorption and emission studies strongly indicate the presence of dynamic quenching for PPV polymers in different solvents (toluene and Triton X-100) in the presence of LiI/I-2. The fluorescence quenching of the PPV polymer by iodide obeys the linear Stern-Volmer equation for PPV/toluene/LiI system. The positive deviation from Stern-Volmer observed in PPV/Triton X-100/I-2 system may be accounted for by the "quenching sphere of action model". Emission studies indicated an increased conjugation length for PPV polymers on going from solution to the solid state. The emission of PPV was readily quenched by hole scavengers such as I- (LiI, I-2). The photoinduced charge transfer to these hole scavengers was studied by laser flash photolysis. The transient absorption measurements confirm the formation of I- and subsequent formation of I-2*(-) which has been reported for the first time for PPV/I-2 system