Improved the optical nonlinearity of carbazole based chromophores via molecular engineering: A DFT approach

The present investigation was based on designing of carbazole based derivatives (DTCFD1–DTCFD8) having D1-π-D2-π-A architecture from DTCFR, upon substituting acceptor motifs for nonlinear optical (NLO) materials. Density functional theory (DFT) analysis at M06-2X/6-311G(d,p) level was accomplished to explore the optoelectronic behavior of designed compounds. The UV–Vis, density of states (DOS), natural bond orbitals (NBOs), transition density matrix (TDM) and frontier molecular orbitals (FMOs) analyses were executed to comprehend the nonlinear optical properties of above-mentioned compounds. The FMO analysis showed DTCFD7 as having the lowest energy gap at 3.734 eV among the derivatives, indicating its potential for efficient charge transfer. The overall decreasing order of band gaps was observed: DTCFR > DTCFD5 > DTCFD3 > DTCFD1 > DTCFD2 > DTCFD4 > DTCFD6 > DTCFD7. UV–Visible analysis exploited that DTCFD7 displayed distinctive absorption characteristics. In the gas phase, it exhibited a λmax of 494.927 nm, while in the dichloromethane it showed a significantly higher λmax of 516.515 nm, then all other derivatives. All the derivatives exhibited greater values of linear polarizability [〈α〉=1.633–1.786 × 10−22 esu], first hyperpolarizability (βtot = 3.690–6.549 × 10−28 esu) and second hyperpolarizability (γtot = 4.825–7.229 × 10−33 esu) as compared to the reference molecule. Furthermore, NLO analysis revealed that the highest βtot (6.549 × 10−28 esu) and γtot (7.229 × 10−33 esu) was exhibited by DTCFD7 and DTCFD1, respectively, then other derivatives. Moreover, a comparative study with standard urea and para-nitroaniline (p-NA), exhibited effective NLO properties in current study compounds. In light of the comprehensive findings, this study concludes that the designed compounds may be considered as effective NLO materials.