Theoretical investigation on the interaction of benzazaborole derivatives with iodide ion: Structural, binding and...

The structural, fluorescence properties and binding interaction of benzazaborole derivatives 1-hydroxy-2-(α-methyl) benzyl-1,2-benzo boron nitrogen heterocyclic-3-phosphate diethyl ester (PADE) and 1-hydroxy-2-(2-chloro) benzyl-1,2-benzo boron nitrogen heterocyclic-3-phosphate diethyl ester (PADC) with iodide ion have been investigated utilizing density functional theory (DFT) and Time-dependent density functional theory (TD-DFT) method, in which the PADE and PADC showed strong emission in aqueous solution and fluorescence quenching was observed upon addition of iodide ion. The theoretical study indicates that the strong hydrogen-bond (O-H…I) between benzazaborole derivatives and iodide ion leads to the formation of the benzazaborole-iodide ion complexes. The excited state properties have been explored by theoretical calculation to understand the fluorescent quenching upon introduction of iodide ion. The strong fluorescent emission is originated by the electron transfer from benzyl and phosphate moieties to benzo boron nitrogen fused heterocycle moiety, while the fluorescence quenching is attributed to the electron transfer between the PADE (PADC) and iodide ion. The density difference (EDD) maps and the frontier molecular orbitals diagrams during excitation and de-excitation process demonstrate that the photoinduced electron transfer process between PADE (PADC) and iodide ion leads to fluorescence quenching after a significant internal conversion.