Study of spectroscopic, reactivity and NLO properties of synthesized dipyrromethane containing cyanovinylhydrazide using experimental and theoretical approaches

In the present work, molecular structure and detailed spectroscopic analysis of a newly synthesized dipyrromethane molecule (3) have been carried out using both experimental and theoretical spectroscopic techniques. Thermodynamic parameters (H, G, S) of all the reactants and products are used to determine the spontaneity of the chemical reaction. Time dependent density functional theory (TD-DFT) is used to calculate wavelength absorption maxima (λmax) of various electronic transitions and their nature within molecule. Natural bond orbitals (NBOs) analysis is carried out to investigate the intramolecular hydrogen-bonding, conjugative and hyperconjugative interactions and their second order stabilization energy (E(2)). The effect of hydrogen-bonding is noticeable in both 1H NMR and FT-IR spectrum as down field chemical shift, vibrational red shift, respectively. The vibrational analysis designates existence of classical hydrogen-bonding (NH⋯N) between pyrrole NH as proton donor and N atom of cyanide as proton acceptor. To investigate the strength and nature of hydrogen-bonding, topological parameters as electron density (ρBCP), Laplacian of electron density ( ∇ ρ BCP 2 ), total electron energy density (HBCP) and estimated hydrogen bond energy (EHB) at bond critical points (BCP) are analyzed by ‘Quantum Theory of Atoms in Molecules’ (QTAIM) in detail. The local reactivity descriptors as Fukui functions ( f k + , f k - ), local softnesses ( s k + , s k - ) and electrophilicity indices ( ω k + , ω k - ) analyses are performed to investigate the reactive sites within molecule. The first hyperpolarizability (β0) of (3) has been computed to evaluate the non-linear optical (NLO) response of the investigated molecule.