Synthesis and fluorescence properties of 2′-benzyloxy flavone—a dual probe for selective detection of picric acid and pH sensing†

Flavonoids are naturally occurring oxygen-containing heterocyclic systems with unique properties for diverse applications. The present study reports the synthesis of a new 2′-benzyloxy flavone and explores its fluorescence sensing properties towards secondary chemical explosives, such as picric acid, and pH sensing. The target 2′-benzyloxy flavone fluorophore (5) was synthesized in three-step reactions with good yield and was fully characterized using NMR, FTIR spectroscopy, and HRMS. The sensing propensity of 5 towards nitroaromatics and pH was probed using fluorescence spectroscopy. Compound 5 exhibited a preferential sensing property for phenolic nitroaromatics with high quenching efficiency for picric acid and differential fluorescence responses for different pH. The superior selectivity of 5 for picric acid is attributed to the intermolecular hydrogen bonding interactions between the O atoms in 5 and the OH groups of picric acid. The observed experimental results were further validated by computational calculations which strongly supported the hydrogen-bond-driven sensing selectivity. Furthermore, selective sensing of picric acid by 5 was further demonstrated in real-water samples and using paper-based sensing. These studies make compound 5 a potential dual sensor for selective sensing of picric acid and sensing of pH of the medium.