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

Our original integral encounter theory is used to describe the photoconduct ivity of p-phenilene vinelene (PPV) accompanied by singlet oxygen generatio n in the polymer volume. This theory allows calculating (a) the free carrie r generation due to the forward electron transfer to oxygen from the excite d singlet of PPV and (b) production of singlet oxygen by energy transfer fr om triplet PPV generated by intersystem crossing. We obtained the stationar y concentration of the free carriers, with account of their geminate recomb ination before separation, as well as the stationary rate of singlet oxygen generation, affected by preliminary quenching of nearest excitations in th e course of ionization. Both effects are related to off-diagonal elements o f the matrix integral equations for the particle concentrations that can be represented in terms of the pair distributions of charged products and pha ntoms of triplet states. The stationary rate constants of electron and ener gy transfer can be easily obtained by the contact approximation, while the charge separation quantum yield and recombination rate constant are accessi ble for analytic calculations within the rectangular model of the remote re action layer for the backward electron transfer. The suppression factor for singlet oxygen generation was obtained in the contact approximation as wel l as numerically for the exponential energy transfer rate. The role of the finite lifetimes of singlet and triplet excitations was especially emphasiz ed. (C) 1999 American Institute of Physics. [S0021-9606(99)70129-7].