Investigation of Solvent Effect and H-Bonding on Spectroscopic Properties of 1-(3-Amino-6-(2,5-dichlorothiophen-3-yl)-4-phenylfuro[2,3-b]Pyridin-2-yl) Ethenone: Experimental and Computational Study

The furo[2,3-b]pyridine moiety is an important scaffold for many biologically active compounds, therefore, the spectral data of the derivative 1-(3-Amino-6-(2,5-dichlorothiophen-3-yl)-4-phenylfuro[2,3-b]pyridin-2-yl) ethenone (FP1) were investigated. Analysis of absorption-pH profile and Forster cycle of FP1 revealed that its excited state is more acidic than its ground state (pK(a)(*) < pK(a)). The main fluorescence emission band of FP1 at 480 nm (in hexane) is shifted to longer wavelengths with increasing polarities of solvents. Linear Lippert's plot and linear correlation between bands maxima and Camlet-Taft parameter, a, of the protic solvents indicated efficient intramolecular charge transfer and noticeable H-bonding. Moreover, the disappearance of the absorption band of FP1 at 385 nm in water, along with the noticeable red shift and quenching of the emission band, and the lower lifetime, relative to nonaqueous solvents, indicate the interruption of the furo[2,3-b]pyridine aromatic moiety. In addition, results from the Time Dependent Density Functional Theory (TDDFT) and Molecular Mechanic (MM) calculations were in agreement with experimentally determined spectra of FP1.