In this publication we conduct calculations on a newly synthesised red-shifted emitter of luciferin in order to understand what are the main contributions to the colour-shifting emission. Indeed the bioluminescent system, especially from fireflies, is one of the main resources for medical imaging but its efficiency greatly depends on the wavelength of the emission. We performed classical molecular dynamics followed by quantum mechanics/molecular mechanics (QM/MM) calculations, with either density functional theory or multiconfigurational reference second-order perturbation theory on different emitters to obtain bioluminescence emission. We analysed the calculations and investigated the effects which play a non-negligible role in the emission, like the effect of the surroundings or the effect of the conformation of the emitter. Finally, in the absence of crystallographic structures, we proposed the most likely conformation for the emitter in the bioluminescence process.