How Do Methyl Groups Enhance the Triplet Chemiexcitation Yield of Dioxetane?

TL;DR

This study investigates how methyl groups increase the chemiluminescence yield of dioxetane by slowing molecular rotation and prolonging the entropic trap, leading to higher light emission efficiency.

Contribution

It provides a detailed mechanistic understanding of methylation effects on dioxetane chemiluminescence through combined simulations and a kinetic model.

Findings

Methyl substitution increases dissociation time.

Rotation around dihedral angle is slowed by methyl groups.

Longer entropic trap duration enhances chemiluminescence yield.

Abstract

Chemiluminescence is the emission of light as a result of a nonadiabatic chemical reaction. The present work is concerned with understanding the yield of chemiluminescence, in particular how it dramatically increases upon methylation of 1,2-dioxetane. Both ground-state and nonadiabatic dynamics (including singlet excited states) of the decomposition reaction of various methyl-substituted dioxetanes have been simulated. Methyl-substitution leads to a significant increase in the dissociation time scale. The rotation around the O-C-C-O dihedral angle is slowed; thus, the molecular system stays longer in the "entropic trap" region. A simple kinetic model is proposed to explain how this leads to a higher chemiluminescence yield. These results have important implications for the design of efficient chemiluminescent systems in medical, environmental, and industrial applications.