Structural and electronic characterization of a Fridericia heliota luciferin-related derivative, based on quantum chemistry

• A natural luciferin-analog was structurally and electronically characterized.
• CompX equilibria consist of six species due to dissociation and tautomerism reactions.
• The properties of this molecule are governed by a strong OH⋯H ionic bond.
• The large Stoke shift was explained by a enol → keto phototautomerization.

CompX is a natural analog of the unknown luciferin of the bioluminescence earthworm Fridericia heliota. Given the difficulties of characterizing luciferin, the objective of this work was the quantum chemistry based structural and electronic characterization of CompX. A main feature of this molecule is a strong partially covalent OH⋯O ionic bond, with sigma bonding character, present in all CompX species. Atomic charge transfers involving this interaction determine the relative stability of all species. Moreover, this interaction is involved in an excited state intramolecular proton transfer leading to a phototautomerism reaction. Thus, the large Stokes shift observed for CompX is attributed to an enol → keto photoconversion.

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