Regioisomeric Control of Chemiexcitation Efficiency in Lophine Silylperoxides through Reaction-Path Topology and Excited-State Accessibility.

This study investigates the chemiluminescence (CL) of silylperoxides derived from lophines and their associated high-energy intermediates (HEIs), specifically 1,2-dioxetanes. Three regioisomeric silylperoxides (D1-3), differing in the position of the -O- group, were synthesized, and their CL and kinetic behavior under fluoride-induced decomposition were examined. Notably, the ortho-substituted derivative (D1) exhibits a 100-fold and 10-fold increase in singlet excited-state formation quantum yield compared to its meta (D2) and para (D3) counterparts, respectively. Computational analysis using density functional theory (DFT) and time-dependent DFT (TD-DFT) indicates that chemiexcitation proceeds through a single-step asynchronous-concerted mechanism with pronounced biradical character along O-O bond cleavage. The differences in singlet quantum yields are rationalized by a combined effect of the extent of the biradical/near-degenerate region and the relative accessibility of excited-state surfaces along the reaction path. In particular, the enhanced efficiency of D1 arises from its prolonged residence in near-degenerate regions together with a more favorable energetic balance for singlet-state formation relative to triplet-state stabilization. These findings provide a mechanistic framework for understanding substituent effects in chemiexcitation and suggest that tuning reaction-path topology and excited-state energetics may guide the rational design of improved chemiluminescent systems.