The bioluminescence process of fireflies is one of the most studied systems. However, some fundamental properties such as the chemical nature of the light emitter (oxyluciferin), have to be further investigated. In this regard, computational studies, in particular the use of quantum mechanical/molecular mechanical (QM/MM) methods, have been essential to better understand this system [1,2].

Here, we study the photochemical properties of the six possible chemical forms of oxyluciferin (obtained by tautomerization and acid-base reactions) and some analogues in water solution by simulating their absorption and emission spectra [3]. This work presents three novelties as it: i) considers both the dynamical information and the interactions between the solute and explicit water molecules; ii) gives a detailed analysis of the electronic nature of the vertical transitions to the first singlet excited state and to upper-lying excited states and iii) compares each natural oxyluciferin form with the corresponding analogues.

Regarding the methodology, each derivative has been placed in a water box and MD have been performed to sample both the ground state and the first singlet excited state minima. Then, the absorption and emission spectra have been simulated as a convolution of the excitation and emission energies of 100 snapshots computed at the QM/MM level of theory using the coupling of the programs G09 (DFT) and TINKER (AMBER force field).

As perspectives, we will study the emission properties of the natural oxyluciferin forms and their analogues inside the protein to get insight into the nature of the light emitter in fireflies bioluminescence.

[1] Navizet I., Liu Y.J., Ferré N., Xiao H.Y., Fang W.-H., Lindh R., J. Am. Chem. Soc. 132, 704 (2010)

[2] Berraud-Pache R. & Navizet I, PCCP, 18, 27460 (2016)

[3] Garcia-Iriepa C., Gosset P., Berraud-Pache R., Zemmouche M., Léonard J., Ferré N., Didier P. and Navizet I. in preparation