PHOTOCHEMICAL CHARGE SEPARATION SUPPRESSED BY SPIN CONVERSION

We present the unified theory of binary triplet state ionization followed by spin conversion to a singlet state of radical ion pair (RIP) and subsequent spin-allowed recombination which hinders the charge separation. An analytical theory of RIPs recombination in contact approximation is developed. At slow diffusion the previous results which ignored the spin states have been confirmed, though the effective recombination constant is weighted with an equilibrium share of singlet state, /4. At faster diffusion, the spin conversion becomes a limiting stage if not completed during encounter and/or delivery time (from the initial distance to contact). The analytical and numerical study of charge separation in polar solutions shows that initial interion distance is an important factor in determining the quantum yield dependence on encounter diffusion and spin conversion rates. At distant starts the diffusional control of geminate recombination gives way to kinetic control and/or to spin conversion control as diffusion increases. At any diffusion the quantum yield of RIPs separation decreases with the magnetic field if the latter accelerates the spin conversion.