On the relationship between fluorescence and molecular geometry. Formation of a luminescent intramolecular anthracene-ethylene exciplex by electronic excitation of lepidopterene

Electronic excitation of the bridged benzenoid hydrocarbon lepidoptene (L) in the crystalline state and in solution gives rise to an anomalous luminescence which is attributed to the radiative deactivation of an intramolecular anthraceneethylene exciplex E*. The formation of E* and the regeneration of L are discussed in terms of a geometry-dependent reversible 4 + 2] cycloaddition. Relevant quantum yield data are presented in an energy level diagram.