Applications of Bioluminescence and Chemiluminescence

Abstract

Chemiluminescence (bioluminescence) arises from the excited states of products of an exothermic reaction. It is analogous to photoluminescence in that the individual excited molecular species are not in thermal equilibrium with their neighbors nor with the solvent molecules. Since relaxation to stable energy levels occurs at rates corresponding to vibrational collision frequencies (ca. 10¹² sec⁻¹) the negative free energy change in the chemical reaction leading to the electronically excited product must occur as a single step. During the lifetime of the excited state (ca. 10⁻⁹ sec) of the product molecule, non-luminescent pathways such as quenching (formation of non-fluorescent excimers), energy transfer to non-fluorescent acceptors and intramolecular radiationless deactivation may compete with the luminescent transition to the ground state. In general, three criteria must be satisfied simultaneously to achieve a sensible chemiluminescence. These are

$$- \Delta F \geqslant \frac{{hc}}{{{\lambda _m}}}$$

where ⋋ is the long wavelength limit for excitation of the product molecule and ∆F is the free energy change for the reaction.

Work supported under AEC Contract AT(11–1)3277.