Diphenyl oxalate (trademark name Cyalume) is a solid whose oxidation products are responsible for the chemiluminescence in a glowstick.

This chemical is the double ester of phenol with oxalic acid.

As the dye relaxes back to its unexcited state, it releases a photon of visible light.

The reaction rate is pH dependent, and slightly alkaline conditions, achieved by adding a weak base, such as sodium salicylate, give a faster reaction and therefore produce brighter light.

[clarification needed] Furthermore, since trichlorophenolate is the better leaving group, the reaction will proceed faster, again producing brighter light, as compared to the phenol ester.