8-Hydroxyquinoline-BODIPY based dual mode pH probe: Intuits acidic and basic environments through two different mechanisms

Abstract

A new BODIPY based optical pH probe that effectively distinguishes acidic and basic solutions through opposite fluorescence responses was designed and subsequently synthesized. The fluorescence response in basic medium was governed by photoinduced electron transfer (PeT). Effective PeT quenched the emission of the probe in basic pH while it was inhibited in acidic pH. The visible colour change on addition of acidic and basic solutions enabled naked eye detection of pH. Comparing the optical property of this probe with other analogous compounds it was realized that substituent at BODIPY has significant impact on possibility of PeT from excited BODIPY moiety. Electron donating substituent facilitates the d-PeT (donor) of excited BODIPY moiety and absence of which inhibits such transition. These experimental observations were validated with theoretical study. The mechanism of pH sensing was also investigated by 1H NMR titration experiment. Interestingly, probe was found to be responsive to pH change in the entire range of pH. Moreover, the probe can reversely detect the pH change through absorption which allows extension of pH sensing in real life samples.