Studies on UV–vis and fluorescence changements in Co2+ and Cu2+ recognition by a new benzimidazole–benzothiadiazole derivative

Abstract

A novel fluorescent sensor (BI-T) was synthesized by the coupling reaction of 2-(2-hydroxyphenyl)-7-phenyl-1H-benzimidazole-4-boronic acid with 4,7-dibromo-2,1,3-benzothiadiazole via Pd-catalysed Suzuki reaction. Its photophysical properties were investigated systematically in different solvents to analyze its potential usage in the fluorescence detection for transition metal ions such as Co2+ and Cu2+ in solutions. In benzonitrile solution, new absorption bands for complex structure of BI-T at 470nm and 580nm were appeared in the presence of Co2+ ions with respect to the uncomplexed form of the sensor absorption. BI-T sensor is usable for both Co2+ and Cu2+ sensation through “on–off” fluorescence change in benzonitrile. In ethanol solution, BI-T shows similar optical performances to detect Co2+ and Cu2+ ions. BI-T detects trace amount of transition metals in ethanol with estimated limit of detection around 4.1×10−7M and 5.5×10−7M for Co2+ and Cu2+ ions, respectively. Possible formation of metal-to-ligand charge transfer (MLCT) state during the titration with Co2+ ion is supported by the detection of long-lived species in the excited state.