It was demonstrated recently that mechanochemiluminescent polymers can be prepared by incorporating mechanoluminophores in their polymer backbone 5, 6, and thermochemiluminescence was also accomplished by heating of deposited nanoparticles 7, 8, 9 and microcrystalline powder 10. If these chemiluminophores are chemically modified to be stable at room temperature, their decomposition can be induced by heating or by application of mechanical force, and the respective phenomena are referred to as thermo- and mechanochemiluminescence. The high-energy reaction intermediates are usually thermally labile hydroperoxides, 1,2-dioxetanes, 1,2-dioxetaneones (1,2-dioxetanones), or 1,2-dioxetanedione 2, 3, 4. The chemiluminescence is also at the core of the generation of ‘cold light’ used in applications that range from glow sticks to single molecule detection and ultra-sensitive tumor bioimaging. When this light is generated by a living organism, in many cases by catalysis in an enzymatic scaffold, the process is known as bioluminescence, and is used by lower biological organisms to communicate, attract prey, or mate 1. Strongly exothermic decomposition of the intermediate subsequently affords products in their electronically excited state, followed by emission of visible light. With selected 1,2-dioxetane, endoperoxide and aroyl peroxide we also establish that the thermochemiluminescence is common for crystalline peroxides, with the color of the emitted light varying from blue to green to red.Įmission of light by chemiluminescence is due to a chemical reaction between reactants in the ground state that results in an unstable high-energy intermediate. Spectral comparison of the thermochemiluminescence in the solid state and in solution revealed that the solid-state thermochemiluminescence of lophine peroxide is due to emission from deprotonated lophine. Heating of crystals of lophine hydroperoxide to ~115 ☌ results in detectable emission of blue-green light with maximum at 530 nm with low chemiluminescent quantum yield. By detecting thermally induced chemiluminescence from centimeter-size crystals of an organic peroxide here we demonstrate direct transduction of heat into light by thermochemiluminescence of bulk crystals. Chemiluminescence, a process of transduction of energy stored within chemical bonds of ground-state reactants into light via high-energy excited intermediates, is known in solution, but has remained undetected in macroscopic crystalline solids.