Time-Resolved Resonance Raman Spectroscopy of Photochemical Reactive Intermediates: Radical Cation of Fluorene and Triplet State of Fluorene, Dibenzofuran and Dibenzothiophen

The time-resolved Raman spectra of the first triplet state–in resonance with theT n ← T 1absorption at370 nm–and of the radical cation transient–in resonance with theR + ⋅ ∗← R + ⋅absorptions at 370 nm andin the 560-600 nm range-are reported for fluorene. The triplet state Raman spectra of dibenzofuran anddibenzothiophen are also given. The vibrational assignments, resonance Raman activity and intensityenhancement effects are studied. On this basis, the structures and electronic configurations of the tripletstate and radical cation transients and the nature of the resonantT n ← T 1andR + ⋅ ∗← R + ⋅transitions arediscussed. It turns out from this investigation that the title molecules present close analogies withbiphenyl. The insertion of a methylene group or a heteroatom does not disturb markedly the electronicproperties of the ground state, the first triplet state and the radical cation transient of biphenyl.