Bimolecular hole transfer quenching of the 1,3,5-trimethoxybenzene radical cation (TMB center dot+) in the excited state (TMB center dot+*) by hole quenchers (Q) such as biphenyl (Bp), naphthalene (Np), anisole (An), and benzene (Bz) with higher oxidation potentials than that of TMB was directly observed during the two-color two-laser flash photolysis at room temperature. From the linear relationships between the inverse of the transient absorption changes of TMB center dot+ during the second 532-nm laser excitation versus the inverse of the concentration of Q, the rate constant of the hole transfer from TMB center dot+* to Q was estimated to be (8.5 +/- 0.4) x 10(10), (1.4 +/-0.7) x 10(11), (1.3 +/- 0.6) x 10(11), and (6.4 +/- 0.3) x 10(10) M(-1)s(-1) for Bp, An, Np, and Bz, respectively, in acetonitrile based on the lifetime of TMB center dot+*. The estimated rate constants are larger than the diffusion-controlled rate constant in acetonitrile. Short lifetime, high energy, and high oxidation potential of TMB center dot+* cause the lifetime-dependent quenching process or static quenching process as the major process during the quenching of TMB center dot+* by Q as indicated by the Ware's theoretical model. The subsequent hole transfer from Q(center dot+) to TMB, giving TMB center dot+, was found to occur at the diffusion-controlled rate for Bp and An as Q. For Q such as Np and Bz, the dimerization of Q(center dot+) with Q to give dimer radical cation (Q(2)(center dot+)) occurred competitively with the hole transfer from Q(center dot+) to TMB.