The spectral characteristics of N,N-dimethyl-4-(4-methyl-4H-imidazo[4,5-b]pyridin-2-yl)benzenamine (PyN-Me), 1-methyl-2-(4'-(N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (ImNH-Me), and 2-phenylimidazo[4,5-b]pyridine (PIP) are investigated to understand the mechanism of protic solvent induced dual fluorescence of 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b). No dual emission is observed from PyN-Me where pyridyl nitrogen blocked from hydrogen bonding with protic solvents confirms the importance of hydrogen bonding of protic solvents with the pyridyl nitrogen in dual emission of DMAPIP-b. Like DMAPIP-b, ImNH-Me also exhibits weak emission and has a shorter fluorescence lifetime in methanol. However, single emission is observed from ImNH-Me in all solvents including protic solvents. This suggests that the imidazole >NH hydrogen also plays a role in the dual emission process. The longer wavelength emission of DMAPIP-b in water increases with increase in pH of the solution owing to deprotonation of the imidazole >NH group. On the basis of these results, the mechanism for the dual emission of DMAPIP-b is proposed.

Push-pull type fluorophores are often exploited as a biological probe because of their high environment-sensitivity nature. Herein, we report the potentiality of a push-pull fluorophore, 2-formyl-5-(4'- N, N-dimethylaminophenyl)thiophene, as a membrane probe. This molecule exhibits strong absorbance in the violet region (∼400 nm) and a high emission quantum yield (≤0.6). The emission is highly sensitive to the surrounding environment, and a high Stokes shift (>7000 cm) appears in strong polar solvents. The molecule is highly susceptible to the fluorescence quenching by protic solvents. The neutral probe efficiently senses aprotic environments such as lipid bilayer membranes through all six fluorescence parameters: emission maxima, intensity, and anisotropy as well as the corresponding time-dependent parameters. The small and flat shape, nonemissive nature in the aqueous medium along with the high susceptibility to all six fluorescence parameters of the molecule strongly suggests a promising fluorescence probe for biological medium.

The double excited state intramolecular proton transfer (ESIPT) of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole (bis-HPTA) has been investigated and found to undergo a new type of proton transfer.

Logic gates with different radixes have been constructed using a biologically active molecule, 2-(4'-N,N-dimethylaminophenyl)imidazo[4,5-b]pyridine (DMAPIP-b). Taking advantage of the multiple binding sites of the fluorophore, a series of different molecular logic gates are developed using fluorescence intensities at different wavelengths. The high emission of the molecule is drastically quenched in the presence of Fe(3+). It is regained by the addition of an equivalent amount of F(-). The fluorescence On-Off nature has been used to construct molecular full subtractor and molecular keypad lock system with Boolean logic. A ternary system is generated by considering three defined fluorescence intensities at particular wavelengths. The smooth dependency of emission intensities with analyte concentration is utilized to construct an infinite-valued fuzzy logic system. The fuzzy logic system is further coupled with a neuro-adaptation method to predict more accurately the dependency of molecular intensity on external inputs.

Proton transfer triggered proton transfer (PTTPT) of the molecule is completely altered by dimethylformamide and the proton transfer paths are changed. The process can be reversed by silver particle.