Chemiluminescence of a Firefly Luciferin Analogue Reveals that Formation of the Key Intermediate Responsible for Excited State Generation Occurs on a Fully Concerted Step.

The chemiluminescence (CL) reaction of eight different 2-(4-hydroxyphenyl)-4,5-dihydrothiazole-4-carboxylate esters with an organic superbase and oxygen was investigated through a kinetic and computational study. These esters are all analogues to the luciferin substrate involved in efficient firefly bioluminescence. The kinetic data obtained from CL emission and light absorption assays were used in the context of linear free energy relationships (LFER); we obtained the Hammett reaction constant ρ = +1.

Evidence for the Formation of 1,2-Dioxetane as a High-Energy Intermediate and Possible Chemiexcitation Pathways in the Chemiluminescence of Lophine Peroxides.

A kinetic study of the chemiluminescent (CL) reaction mechanism of lophine-derived hydroperoxides and silylperoxides induced by a base and fluoride, respectively, provided evidence for the formation of a 1,2-dioxetane as a high-energy intermediate (HEI) of this CL transformation. This was postulated using a linear Hammett relationship, consistent with the formation of negative charge on the transition state of HEI generation (ρ > 1). The decomposition of this HEI leads to chemiexcitation with overall low singlet excited state formation quantum yield (Φ from 1.

The decomposition of triphenylimidazole-para-acetate follows specific base catalysis and can be conveniently followed by fluorescence.

The kinetics of the decomposition reaction of 4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl acetate (1) in basic alcoholic media was investigated, using a simple fluorescence (FL) spectrophotometric procedure. The process was conveniently studied using FL, since the triphenylimidazole-derived ester 1 and its reaction products (the corresponding phenol 2 and phenolate 2 ) are all highly fluorescent (Φ  > 37%). By carefully selecting excitation and emission wavelengths, observed rate constants k in the order of 10 to 10  s were obtained from either reactant consumption (λ  = 300 nm, λ  = 400 nm) or product formation (λ  = 350 nm, λ  = 475 nm); these were shown to be kinetically equivalent.