The photoconductivity-detected magnetic resonance (PCDMR) spectrum observed in the photoinduced electron-transfer reaction of xanthone and N,N-diethylaniline in 2-propanol shows a peculiar spectral shape by microwave radiation with high power. The resonance center of the spectrum shows a spin-locking effect, and the wing portions show a broadened transition (pumping). When the lifetime of the radical-ion pair (RIP) becomes longer by controlling the solvent property, the wing portions become larger. We try to clarify the relation between the broadened wings and the lifetime of the radical-ion pair by the calculation employing the spin-dephasing effect. We conclude that the broadness appears under high microwave power conditions and the existence of effective triplet-triplet dephasing (TTD). TTD is the spin-phase relaxation between the triplet states of the radical-ion pair, and this relaxation may be mainly induced by the modulation of electron spin dipole-dipole interaction. The long lifetime of the present RIP system and its spin relaxation phenomena suggest the transient formation of a RIP confined strongly in a solvent cage or a structured RIP involving solvent molecule(s).