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 470 nm and 580 nm 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 × 10⁻⁷ M and 5.5 × 10⁻⁷ M 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.