Domino-like turn-on chemiluminescence amplification: Opening a gateway through proximal-imidazole species formation...

Due to their extremely low background signal and high sensitivity, the chemiluminescence (CL) probes have received a great attention in various chemical and biological applications. However, the lack of selectivity is still a challenging task. As an innovative topic of research, in this work we developed a domino-like turn-on CL reaction through proximal-imidazole species for the first time. The oxidation reaction of N-(2H-[1,2,4]thiadiazolo[2,3-a]pyridine-2-ylidene)benzamide (1) by hydrogen peroxide found to promoted by a domino-like reaction between proximal imidazole species and the Co²⁺-1 complex formation which accompanied by a dramatically turn-on emission. In the way of explaining the possible mechanism, the application of density functional theory (DFT) studies revealed that there are three possible pathways for the reactions between precursor 1 and HOO^- in the presence of imidazole to produce the oxidized isomers. The strongest interaction found to occur in pathway 3, in which the sulfur atom was oxidized, while there was some repulsion between HOO^- and 1, due to the effects of two different charges in pathways 1 and 2. To confirm tits applicability, the CL system was successfully applied to highly selective quantification of vitamin B₁₂ in some real samples. The linear dynamic range was achieved from 0.08 to 34 ng mL^-1 and the detection limit was evaluated as 0.028 ng mL^-1. This new method introduced fluorescence selectivity and CL sensitivity in single technique. It was finally anticipated that the CL amplification through proximal-imidazole species possesses a great potential on tuning various color-emissions based on different metal-ligand complex formations studied.