A novel photolabile analogue of coelenterazine with a trifluoromethyl diazirine group is successfully synthesized for photoaffinity labelling of the active site of aequorin; preliminary studies on its chemi-and bio-luminescence demonstrate that the photolabile analogue shows the same luminescence properties and kinetics as those of natural coelenterazine and thus, it is deduced that both compounds occupy the same active site of aequorin.