Deciphering Spectroscopic and Structural Insights into the Photophysical Behavior of 2,2'-Dipyridylamine: An Efficient Environment Sensitive Fluorescence Probe.

Excited state deactivation properties and the effects of solvent hydrogen bonding (HB) on the photophysical behavior of 2,2'-dypyridylamine (DPyA) were investigated by steady state and time-resolved fluorescence experiments, molecular docking, and density functional theory (DFT) calculations. In addition to the polarity effect, the contributions of solvent HB donation (HBD) acidity and HB acceptance (HBA) basicity to modulate the solvatochromic spectral properties were estimated from multiparametric linear regression analysis using Kamlet-Taft (KT) and Catalán formalisms. The importance of C-N bond torsion, leading to the → conversion, was manifested by substantial increase in DPyA fluorescence yield in the presence of cyclodextrin (CD) and glycerol. The unusually low fluorescence yield in aqueous medium was explained on the basis of synergistic effect of solvent hydrogen bonding combined with excited state conformational isomerization, which renders DPyA to be an excellent environment sensitive fluorescence reporter. The experimental results were verified with structural insights obtained from DFT calculations at B3LYP/6-311++G(d,p) level and construction of potential energy surface (PES) in the ground state as well as in the excited states.