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

Abstract

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 trans → cis 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.

Fluorescent Molecular Rotors Based on Hinged Anthracene Carboxyimides

“…Hence, the multi-parameter approach proposed by Kamlet–Taft [ 6 , 7 , 8 , 9 ] and Catalán [ 10 , 11 , 12 , 13 ] was employed in order to further study and explain the solvatochromism. These two multi-parameter methods have been successfully applied to various physiochemical processes, working with, for example, UV–Vis absorption centers [ 33 ], emission centers [ 33 ], Stokes shifts [ 33 ], quantum yields [ 34 ], radiative and non-radiative rate constants [ 34 ], and fluorescent lifetimes [ 34 ]. Kamlet–Taft and Catalán solvatochromic equations are expressed as Equations (3) and (4), respectively: where y represents a solvent-affected physiochemical characteristic, such as UV–Vis absorption center ( ν Abs ), emission center ( ν Em ), and Stokes shift (Δ ν St ), y 0 is the observed characteristic, a α , b β , and c π* are the coefficients that show the relationship between y and various solvent properties, α is the solvent acidity, β is the solvent basicity, π* is the coefficient of solvent polarity, polarizability, and dipolarity.…”

Geometric Analysis and DFT Study of 2,2′-Dipyridylamine-Stabilized First-Row Transition-Metal Complexes

“…The flexibility and nucleophilicity of this ligand have been harnessed for the synthesis of various metal complexes which are used as catalysts and other photophysical materials . This ligand usually coordinates to a metal ion in a bidentate fashion with the N-donor atoms on the pyridine rings, as shown in Figure b although several other coordinating modes have also been reported.…”