A new benzimadazole based solid state chemosensor 5, 6-Dimethyl-2, 2′-bis-1H-benzimidazole (here after R-1) was reported. Sensor R-1 showed high selectivity and sensitivity towards fluoride and acetate anions over the series of tested anions in solid state as well as in CH3CN medium. A distinct colour change of R-1 from yellow to deep green and finally brown, was observed through a –NH deprotonation mechanism. Photophysics, 1H NMR, Cyclic voltametry and DFT based computation justified this colour change with profound support of extraction of –NH proton from R-1. © 2017 Elsevier B.V.