Tyrosine derived fluorescent molecular probes as solvent mediated flip-flop halide (iodide/fluoride) sensors and reversible chromogenic pH indicators

In this work, we have developed two single-molecular probes, ( S )-3-(4-hydroxyphenyl)-2-((4-nitrobenzyl)amino)propanoic acid (H 2 Tyr-4-nitro, 1 ) and ( S )-3-(4-hydroxyphenyl)-2-((3-nitrobenzyl)amino)propanoic acid (H 2 Tyr-3-nitro, 2 ), from cheap and readily available l -tyrosine and demonstrated their use as (i) a solvent mediated differential fluorescent sensor for iodide in aqueous methanol and fluoride in aqueous DMSO and (ii) a reversible chromogenic pH indicator in DMSO. A flip-flop halide sensor also acting as a pH indicator is unprecedented. We report the use of l -tyrosine derived probes (H 2 Tyr-4-nitro/H 2 Tyr-3-nitro) for solvent mediated differential flip-flop sensing of fluoride and iodide and as reversible optical pH indicators.