Information on the chemiluminescence mechanism of the firefly from MNDO molecular orbital calculations

Abstract In order to obtain information on the chemiluminescence mechanism of the firefly, MNDO molecular orbital calculations were carried out for decarboxyketoluciferin, decarboxyenolluciferin and its enolate anion (EA) and phenolate-enolate dianion, which may be directly concerned in the chemiluminescence. For the four compounds, the transition from the lowest unoccupied molecular orbital to the highest occupied molecular orbital is expected to give rise to emission of UV or far-UV light, yielding no visible light. However, among the four chemical species, which might be generated by transfer of one electron from each compound to luciferase, only the excited species from EA can emit yellow light. The wavelength of the yellow light is in good accordance with the observed light of fireflies. Lower value of the heat of formation of EA, compared with that of the three other compounds, also favors formation of the excited state.