Synthesis and photophysical studies of new hybrid 2,2′-bipyridine/carbazole fluorophores

A series of 2,2′-bipyridine-carbazole hybrids have been synthesized via the sequence of of SNH reaction of 3-(pyridin-2-yl)-1,2,4-triazines and Boger reaction. The UV–Vis absorption and photoluminescence properties of the obtained compounds have been studied. The solvent effect studies have been carried out using Lippert-Mataga equation as well as Dimroth-Reichardt scales revealing a positive solvatochromic effect, suggesting the presence of ICT luminescence mechanism, which was further confirmed by theoretical calculations. Two of the obtained fluorophores exhibit a turn-off luminescent response upon the gradual addition of PA with Stern-Volmer constant of 1.46 × 105 M−1 and 3.69 × 104 M−1, and quenching efficiency values of 41.3% and 31%. The LOD values are 180 ppb and 68 ppb. Based on DFT calculations and the titration data, a combination of IFE and pseudostatic PET quenching mechanisms has been proposed.