ICT based ratiometric fluorescent pH sensing using quinoline hydrazones

Two new quinoline hydrazones were synthesized, characterized and investigated as reversible ratiometric fluorescence pH sensors in the acidic pH region. The sensors were designed by the formation of simple donor-acceptor couple of quinoline aldehyde and phenyl hydrazine where protonation of quinoline-N triggered the pH sensing. No significant interference on emission behavior was observed in the presence of various metal ions. The sensors were used to visualize HeLa cells both at acidic and neutral pH with different emission. The MTT assay revealed negligible toxicity for both the hydrazones. The spectral properties, especially the large Stokes shift and the geometry of the molecules at the ground and excited states had been rationalized through DFT and TDDFT studies.