Broad range ON/OFF pH sensors based on pKa tunable fluorescent BODIPYs

A set of highly fluorescent, pH-responsive boron dipyrromethene dyes covering the pH range of 5-12 is presented for broad range pH measurements in mixed aqueous-organic media and polymer matrices. Readout in the intensity domain with low cost and miniaturized instrumentation utilizes reversible protonation induced switching ON of their initially completely quenched fluorescence mediated by photoinduced electron transfer. All dyes, rationally designed to reveal closely matching absorption and emission properties, are accessible via facile two-step reactions in overall yields of up to 20%. By modifying the substitution pattern of the meso-aryl substituent, the pKa values could be fine-tuned from 6 to 11. Integration of these molecules into polymeric films by a simple mixing procedure yielded reversible and longterm stable pH sensors for naked eye detection. (C) 2017 Elsevier B.V. All rights reserved.