Effect of concentrations of radical-ion intermediates in the photochemicalredox reaction of the diphenylmethyl radical

Effect of concentrations of radical ion intermediates in photoinduced elect ron transfer (PET) reactions was examined for the redox reaction of dipheny lmethyl radical. The irradiation of sym-tetraphrnylacetone in the presence of aromatic donor and acceptor in MeOH-MeCN (1:9) leads to (i) the simultan eous generation of diphenylmethyl radical and a pair of radical ions, (ii) the electron transfers between them affording diphenylmethyl cation and ani on, and (iii) the formation of Ph2CHOMe and Ph2CH2 by the trapping reaction s with methanol. The product ratios of Ph2CH2/Ph2CHOMe are shown to be domi nated by the steady-state concentrations of radical ions. Thus, pulsed irra diations resulted in quite different product ratios depending on the pulse intervals. The relative rates extrapolated to infinite, which are directly related to the intrinsic electron transfer rates with radical ions: are sho wn to follow the Rehm-Weller-type relationship. The importance of the persi stent radical ion effect for PET reactions, just as the Ingold-Fischer pers istent radical one, is discussed. (C) 1999 Elsevier Science S.A. All rights reserved.