Year: 2026
Type: preprint
Abstract: We report a quantum-chemical investigation into the chemiluminescence mechanism of cyclometalated Ir (III) Schiff base complexes, promising chemiluminophores for biological imaging. The reaction proceeds via ring-opening of a key oxaziridine intermediate to yield a singlet diradical, which undergoes rapid intersystem crossing (ISC) to its triplet counterpart, followed by deprotonation to generate the emissive triplet product. Within this process, the Ir (III) center not only activates the imine via Lewis-acid coordination but also reverses the singlet-triplet energy ordering of the diradical intermediate, rendering the triplet diradical thermodynamically favored with an equilibrium population of ca. 86% at ambient temperature. The heavy-atom effect of iridium provides substantial spin-orbit coupling; combined with a low-lying minimum-energy crossing point (MECP, 1.7 kcal mol -1 ) and large Franck-Condon-weighted density of states, this accelerates ISC to a rate of 1.5 × 1011 s -1 . Notably, the two radical centers are separated by an 𝑠𝑝3-hybridized carbon, and the intervening C-H bond is strongly polarized by the adjacent O-centered radical, rendering deprotonation nearly barrierless. These collective computational findings establish design principles for two distinct goals: stabilizing diradical species to extend their lifetimes for EPR characterization, and informing the rational development of non-precious-metal chemiluminescent systems.
Source: ChemRxiv
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221121001