Two D-π-A type fluorescent probes based on isolongifolanone for sensing acidic pH with large Stokes shifts

Two novel isolongifolanone derivatives (2-3) with D-pi-A configuration, which had a N,N-dimethylaniline unit attached to pyrazole and pyrimidine cores, were synthesized and characterized by IR, NMR and HRMS. As the protonation of the nitrogen atoms, the probes 2-3 displayed the significant pH dependent spectral properties. The probe 2 exhibited a remarkable ratiometric fluorescence emission (I-445/I-373) characteristic with pK(a) 2.59 and the linear response over the extremely acidic range of 1.5-4.0. The probe 3 showed an obvious emission quenching at (lambda(ex) nm 300 nm) with a pK(a) of 3.69 and responded linearly to monitor the pH fluctuations with the weakly acidic range of 3.5-7.0, while exhibited a linear emission enhancement at 519 nm (lambda(ex) = 425 nm) over the extremely acidic range of 1.0 -3.5. These pH probes also displayed favorable features including large Stokes shift under acidic conditions, high selectivity, rapid response, excellent photostability and good reversibility for sensing acidic pH which were further applied to response to acidic solid and gas phase using their solid-state samples, causing dramatic fluorescence color changes. In addition, the logic gates for probe 2 were constructed to develop its potential for practical applications. (C) 2018 Elsevier Ltd. All rights reserved.