The spectral-structural relationship of a series of oxyluciferin derivatives.

The absorption and emission spectra of a series of oxyluciferin derivatives with different substituents, as well as 6'-amino oxyluciferins in different enol and keto forms, with or without an active-site model of luciferase, were systematically investigated using density functional theory. The effects of substituents, microenvironment, and the luciferase on the structures, absorption spectra, and fluorescent emission were all taken into account. It was found that a wide range of emission colors can be obtained from various oxyluciferin derivatives with the inclusion of active site residues modeling the luciferase active site. Enol and keto forms are responsible for the emissions observed in experiments. It was suggested that the active site of luciferase must be included in the calculation in order to determine the form of the emitters.