Ab initio investigation on the chemical origin of the firefly bioluminescence

The chemical origin of the firefly bioluminescence has been investigated by means of density functional and multireference theoretical methods. Different hypotheses on the mechanism of multicolour emission have been investigated: twisting around the central carbon–carbon bond, polarizability of the oxyluciferin microenvironment and presence of resonance structures. The calculated results indicated that the higher the polarizability of the microenvironment is, the larger the red shift of the bioluminescence is. Moreover, a quite flat potential energy surface should allow the easy shifting of the anion minimum between different pseudo-resonance structures. The possible effects of a tight or loose protein pocket has also been considered.