A long-lived radical-ion pair formed in the photoinduced electron-transfer reaction of xanthone and NN-diethylaniline in 2-propanol is studied using a time-resolved ESR method. The spectrum shows the spin-correlated radical pair with emissive spin polarization of the triplet mechanism. According to the analysis, it is concluded that the radical-ion pair formed transiently has a cluster-like structure by the formation of a network with the surrounding solvent molecules in the present particular system. (c) 2006 Elsevier B.V. All rights reserved.