Photoconductivity and singlet oxygen generation in illuminated polymer in the air atmosphere

Our original integral encounter theory is used to describe the photoconductivity of p-phenilene vinelene (PPV) accompanied by singlet oxygen generation in the polymer volume. This theory allows calculating (a) the free carrier generation due to the forward electron transfer to oxygen from the excited singlet of PPV and (b) production of singlet oxygen by energy transfer from triplet PPV generated by intersystem crossing. We obtained the stationary concentration of the free carriers, with account of their geminate recombination before separation, as well as the stationary rate of singlet oxygen generation, affected by preliminary quenching of nearest excitations in the course of ionization. Both effects are related to off-diagonal elements of the matrix integral equations for the particle concentrations that can be represented in terms of the pair distributions of charged products and phantoms of triplet states. The stationary rate constants of electron and energy transfer can be easily obtained by the contact approximation, while the charge separation quantum yield and recombination rate constant are accessible for analytic calculations within the rectangular model of the remote reaction layer for the backward electron transfer. The suppression factor for singlet oxygen generation was obtained in the contact approximation as well as numerically for the exponential energy transfer rate. The role of the finite lifetimes of singlet and triplet excitations was especially emphasized. (C) 1999 American Institute of Physics. [S0021-9606(99)70129-7].