DFT study of structural and electronic properties of 1,4-diarylcyclopenta[d] pyridazines and oxazines for non-linear optical applications.

Polymer and molecular-based electronic materials incorporating heterocycles like thiophenes and pyrroles are attractive possibilities as substitutes for semimetal materials. Heterocyclic materials are heavily studied in this regard due to the large variations in possible substrates. Herein we evaluated four different 5,6-fused ring heterocycles to gain a better understanding of any favorable optical and electronic properties that were due to incorporation of certain moieties. The molecules chosen would highlight the effects that the central ring (pyridazine versus oxazine), aromatic substituent, and heterocyclic side group may have on electronic and optical properties. Computational analysis of these four molecules was done using density functional theory (B3LYP and PBEPBE) with 6-31G(d,p), 6-311 ++G(d,p), and cc-pVTZ basis sets. The constituent molecules were optimized, and calculations were done for the dipole moment, polarizability, first-order hyperpolarizability (β), HOMO and LUMO orbitals, and a natural bonding order (NBO) analysis. These calculations allow for the study of charge density via electrostatic potential mapping and bonding orbitals. The results indicated that the pyridazine molecules presented here are more favorable than the oxazines for non-linear optical (NLO) applications. It is also noted that side ring substituents (thienyl and furyl) in the two pyridazines studied showed very little calculated differences. Finally, heterocyclic rings showed more favorable properties when incorporated as substituents for NLO applications over hydrocarbon aromatics. Graphical abstract.