NLO potential exploration for D–π–A heterocyclic organic compounds by incorporation of various π-linkers and acceptor units

Abstract

Heterocyclic compounds with excellent nonlinear optical (NLO) properties are highly significant and have many potentials uses in various fields such as nuclear science, optoelectronics etc. Herein, an organic dye JK-201 was used theoretically to design a series of novel D-π-A based NLO molecules (DTA1-DTA12). This novel series of NLO molecules was quantum chemically designed by structural tailoring at the 1st π-spacer and acceptors unit of the JK-201 molecule. To explore the effect of spacers and acceptors on the electronic, photophysical, and NLO properties of DTA1-DTA12, density functional theory (DFT) investigations were performed for different simulation analyses. UV–Vis spectra revealed that all these novel compounds exhibited broader absorption spectra with the largest shift and a narrowed bandgap (1.84–2.07 eV) compared to the parent molecule (JK-201). Among all the designed compounds, the largest redshift was examined in DTA11 (538.99 nm). Furthermore, with the help of frontier molecular orbital (FMO) study, charge transfer processes between the orbitals and chemical reactivity of designed molecules were explained. Moreover, the Energy gap (ELUMO-EHOMO) was also used to express global reactivity parameters (GRPs). These GRP findings evaluated that all molecules (DTA1-DTA12) had higher global softness (σ = 13.15–14.77 a.u) and lower hardness (η = 0.034–0.038 a.u) values, which indicated that these compounds were more reactive. Nevertheless, significantly higher NLO behavior was examined in all compounds. Overall, compound DTA5 showed a larger value of the linear polarizability (= 2868.08 a.u.), while compound DTA12 displayed a larger hyperpolarizability (βtotal = 268494.71 a.u) value. This present work presented that by controlling the type of π-spacer and acceptor units, metal-free NLO materials can be designed, which can be valuable for hi-tech NLO applications.

Keywords

• Density functional theory (DFT)
• π-conjugated linkers
• NLO properties
• Structural modifications