Replacing 1, 10-phenanthroline fluorophore with benzil: A structural modification for selectivity.

The sensing ability of 2-(anthracen-9-yl) -1H-imidazo [4, 5-f] [1, 10] phenanthroline ( 1 ) has been exhaustively investigated towards cations and anions using UV–vis and fluorescence spectroscopy in CH 3 CN. 1,10-phenanthroline played a major role in both cation and anion recognition as 1 exhibited little and medium selectivity towards cations and anions respectively. 1 exhibited fluorescence quenching with all the tested transition metal ions of first transition series, based on photoinduced electron transfer. The basic anions (CN - , F - and AcO - ) exhibited new absorption bands and quenching of fluorescence emission intensity with 1 indicating deprotonation of imidazole NH (pK a = 11.05). To establish the undesirable role of 1, 10-phenanthroline and to improvise upon the selectivity, a model chemosensor 2 was synthesized containing benzil instead of phenanthroline. Both, the non availability of phenanthroline N's and decreased acidity of imidazole NH in 2 (pK a = 11.96) were expected to enhance selectivity of 2 for cations and anions respectively. Interestingly, the results of detailed photophysical examination of 2 in CH 3 CN revealed 2, a better and selective chemosensor for cations and anions than 1 . Moreover , 2 manifested colorimetric sensing response, exclusively for Cu 2+ ions by a distinct color change from colorless to greenish yellow. [ABSTRACT FROM AUTHOR]