Direct fluorescence lifetime measurement of excited radical cation of 1,3,5-trimethoxybenzene by ns–ps two-color two-laser flash photolysis

The fluorescence spectrum with a peak around 620 nm and lifetime of 41 ± 2 ps for 1,3,5-trimethoxybenzene radical cation (TMB+) in the excited state (TMB+∗) were directly measured with ns–ps two-color two-laser flash photolysis at room temperature. The fluorescence of TMB+∗ is assigned to the D2 → D0 transition, showing that TMB+ is one example of radical cations which violate Kasha’s rule. The fluorescence quantum yield of TMB+∗ was determined to be 5.4 × 10−3, and the radiative and nonradiative decay rate constants were 1.3 × 108 and 2.4 × 1010 s−1, respectively.