Effect of Structural Variation on Spectral, NLO Properties, and Biological Activity of Pyrrole Hydrazones.

This paper describes spectral, non-linear optical (NLO), and biological activity variation of pyrrole hydrazones as a result of structural variation. In order to study structure-property variation, pyrrole hydrazones (, , and ) were synthesized in both solid and solution phases. The grinding solvent-free method becomes rapid, easy, convenient, useful, sustainable, and eco-friendly green synthesis as compared to the classical solution phase reactions. The structure of pyrrole hydrazones has been elucidated by microanalysis and quantum chemical calculations. The intense emission at λ 521 nm ( and ) and 617 nm () in the visible (green and orange) region with Stokes shifts at 195, 160, and 282 nm reveals that the studied compounds work as good photoluminescent materials. All compounds show strong n-π* and charge transfer (π-π*) transitions in the UV-vis region with high extinction coefficients. In the studied systems (, , and ), the orbital overlap between σ(NH-O) → σ*(NH-O) is found due to intra-molecular charge transfer. The first hyperpolarizabilities were found to be 48.83 × 10 esu for and 63.89 × 10 esu for showing variation with structure. Their high values indicate more suitability for NLO application. Incorporation and/or change in position of electron-withdrawing groups increase the β values of and compared to . The β value also increases monotonically as the polarity of the solvents increases. The red shift in N-H and C=O stretching Fourier-transform infrared bonds is due to the formation of dimers. The synthesized , , and show good antimicrobial activity and are predicted to be potential antibacterial and antifungal drugs. The has more molar refractivity (122.16 esu) than and and correlates well with the calculated binding affinity and experimental antimicrobial data.