Spectroscopic, reactivity and NLO analysis of new hydrazone-containing dipyrromethane using experimental and theoretical approaches

The molecular structure and detailed spectroscopic analysis of a novel synthesized dipyrromethane: 1,9-bis[(2-hydroxybenzoyl)-hydrazonomethyl]-5-(2-nitrophenyl)-dipyrromethane (3) have been performed using both experimental techniques and theoretical calculations. Thermodynamic parameters (H, G, S) of reactants and products have been used to investigate the nature of synthesis. The singlet chemical shift at 5.343 ppm of meso-proton designates formation of product molecule (3). TD-DFT has been used to calculate oscillatory strength (f) and wavelength absorption maxima (λmax) of various electronic excitations and their nature within molecule. The molecular orbital coefficients and molecular plots analysis assign nature of electronic excitations as π → π*. Natural bond orbital (NBO) analysis has been carried out to investigate the intramolecular H-bonding, conjugative and hyperconjugative interactions within molecule. The result of intramolecular hydrogen bonding (O68H69⋯O22/O66H67⋯O45) is obvious in 1H NMR, FT-IR and NBO due to down field chemical shift, vibrational red shift, and n2(O22) → σ*(O68H69)/n2(O45) → σ*(O66H67) interactions energies 105.12/104.91 (kJ/mol), respectively. To investigate the strength and nature of H-bonding, topological parameters at bond critical points (BCP) have been analyzed by ‘Quantum theory of Atoms in molecules’ (QTAIM). Local reactivity descriptors- Fukui functions ( f k + , f k - ) , local softnesses ( s k + , s k - ) and electrophilicity indices ( ω k + , ω k - ) analyses have been performed to find out the reactive sites of the molecule. The computed first hyperpolarizability (β0 = 14.30 × 10−30 esu) evaluates the molecule to be suitable for non-linear optical (NLO) response.