A theoretical investigation of the possible mechanisms for detection the copper ions by a retinal-base sensor

The first report of retinal-based structures as the fluorescent probe is a retinal-phenylenediamine structure which experimentally has been shown can turn on in response to Cu2+. Despite the favorable experiment results of the sensor action, no exact mechanism proposed until now. Therefore, the density functional theory (DFT) is utilized to recognize the sensing mechanism. Based on the results of these calculations, two mechanisms could be sug-gested. The first proposed mechanism can proceed by changing the oxidation state of Cu2+ to Cu1+. The second proposed is based on the catalyst role of Cu2+ in the ring-closing mechanism. The frontier molecular orbitals and NBO analysis show that fluorescence enhancement has roots in suppressing CN isomerization.