The bioluminescence process corresponds to the emission of visible light through a chemical reaction in living things. Those species can be found all around the globe from mushrooms and worms on land to jellyfish in the ocean. Recently, an experimental team has synthesized a new luciferin analogue [1], the molecule involved in the bioluminescence of fireflies. The luciferin reacts inside a protein, the luciferase, leading to an emitter, named oxyluciferin, which emits in the yellow-green area of the visible spectra. The emitter produced from the new luciferin analogue gives an emission near the infrared. The red emission obtained from the new analogue allows a better in-vivo tissue penetration and a better signal quantification in the field of biomedical imaging. In this presentation, I will discuss about the factors that influence the colour tuning of the wavelength emission in the bioluminescence of fireflies. To answer this interrogation a theoretical approach combining classical molecular dynamics (MD) followed by QM/MM calculations (Quantum Mechanics/Molecular Mechanics) has been carried out on the wild oxyluciferin/luciferase system and the red analogue oxyluciferin/luciferase system. The complete study of the system dealing with both the electrostatic and geometric interactions unveils how the bioluminescence emission can be tuned [2]. References [1] A. P. Jathoul, H. Grounds, J.C Anderson and M. A. Pule, Angew.Chem.Int.Ed. 2014 53, 13059 –13063 [2] R. Berraud-Pache, I.Navizet Physical Chemistry Chemical Physics, 2016, DOI: 10.1039/C6CP02585D