LAUSR

Abstract Hydrogen bonding interaction between quercetin (Qc) and different acceptor molecule such as the 3,5-dinitrosalicylic acid (DSA), picric acid (PA), o-chloranil, p-chloranil were studied by spectroscopic and theoretical method. The stoichiometry of complexes were established as 1:3 using Job's plot of the selected systems. It was observed from UV–vis studies that a different absorption maxima i.e., a charge-transfer band arises when individual acceptor molecule mixed with Qc. Further, with increase of acceptors concentration with a fixed concentration of Qc in ground state there appears a one or more isosbestic point in every system which also indicates the strong charge-transfer equilibrium. This is may be owing to the formation of H-bond. Fluorescence quenching experiment was also carried out to make out the Stern-Volmer binding constant (KSV) and the quenching efficiency of the acceptor molecules. FT-IR spectrums of prepared solid complexes and 1H NMR studies of complexes confirms that the complexation has arisen due to the H-bonding interactions. Gas phase DFT optimization and NBO analysis of the complexes reveals the probable occurrence of multiple H-bonding interactions between the Qc and acceptor molecules.