Photodissociation of naphthalene (Np) dimer radical cation (Np-2(center dot+)) to give naphthalene radical cation (Np center dot+) and Np and the subsequent regeneration of Np-2(center dot+) by the dimerization of Np center dot+ and Np were directly observed during the two-color two-laser flash photolysis in solution at room temperature. When Np-2(center dot+) was excited at the charge-resonance (CR) band with the 1064-nm laser, the bleaching and recovery of the transient absorption at 570 and 1000 nm, assigned to the local excitation ( LE) and CR bands of Np-2(center dot+), respectively, were observed together with the growth and decay of the transient absorption at 685 nm, assigned to Np center dot+. The dissociation of Np-2(center dot+) proceeds via a one-photon process within the 5-ns laser flash to give Np center dot+ and Np in the quantum yield of 3.2 x 10(-3) and in the chemical yield of 100%. The recovery time profiles of Np-2(center dot+) at 570 and 1000 nm were equivalent to the decay time profile of Np center dot+ at 685 nm, suggesting that the dimerization of Np center dot+ and Np occurs to regenerate Np-2(center dot+) in 100% yield. Similar experimental results of the photodissociation and regeneration of Np-2(center dot+) were observed during the pulse radiolysis- laser flash photolysis of Np in 1,2-dichloroethane. The photodissociation mechanism can be explained based on the crossing between two potential surfaces of the excited-state Np-2(center dot+) and ground-state Np center dot+.