1971 Volume 44 Issue 3 Pages 629-637
For the analysis of the characteristic nature of the first absorption band of diphenylamine (DPA), calculations of the electronic states of DPA and its analogous compounds, diphenylether (DPE) and diphenylmethane (DPM), were carried out and the solvent effects on the fluorescence spectra of these compounds were investigated. The calculated results show that the first excited states of these three compounds are mainly benzene B2u. However, in DPA, the ionic state (CTs−) is located very closely to the B2u state. It seems reasonable to say, therefore, that, in solution, the ionic state lowers its energy down to the position of the B2u state and that the first absorption band observed in the solution is a superposed band of two transitions, G→B2u and G→CTs−. To confirm this assumption, the value of Δμ, which is the dipole-moment change between the ground and excited states, is estimated from the solvent effect on the fluorescence spectrum. The observed value of Δμ for DPA is intermediate between the theoretical values for the lowest (B2u) and the second excited state (CTs−) ; from this fact it may be inferred that the mixing of CTs− to the lowest excited state (B2u) is increased in the excited equilibrium state.
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