Exploring the NLO potential of new designed thieno[2,3-b]indole-based derivatives via donor group modification: a DFT study on static and frequency-dependent NLO properties
摘要
Several D–π–A compounds (CTFM1-CTFM7) were developed to evaluate their linear and nonlinear optical (NLO) properties. A thieno[2,3-b]indole-based chromophore (CTFM) was selected to design new derivatives by incorporating various electron-donating (D) groups. The designed compounds consisted of dithieno[3,2-b:2′,3′-d]thiophene as the π-spacer and 2-(3-cyano-4-methyl-5-phenyl-5-(trifluoromethyl)furan-2(5-H)-ylidene)malononitrile as the acceptor unit along with a range of strong donors. Density functional theory (DFT) and time-dependent DFT (TD-DFT) were employed to investigate their geometrical and optoelectronic properties utilizing the conductor-like polarizable continuum model (CPCM) to simulate solvent effects in the chloroform medium. Additionally, their optical properties were investigated by calculating the excitation energies and simulating the UV-Visible spectra at the B3LYP/6-311G(d,p) level. The outcomes showed significantly reduced Egap values (1.801–3.228 eV) and bathochromic shifts (551.408–709.901 nm) in the designed chromophores. Particularly, CTFM6 exhibited the least Egap (1.801 eV) and highest absorption wavelength (709.901 nm) was noted for CTFM7. Further, the hyper-conjugation and intramolecular interactions were visualized using the natural bond orbitals (NBOs) analysis. The NLO properties showed prominent results for CTFM7 compound i.e., < α > = 1.77 × 10−22 esu, βtotal = 3.33 × 10−27 esu and γtotal = 3.06 × 10−32 esu. Similarly, frequency-dependent electro-optic Pockels effect (EOPE) i.e., β(− ω,ω,0) and electro-optic Kerr effect (EOKO) i.e., γ(− ω,ω,0,0) also showed the highest values for CTFM7 as 6.25 × 10−25 and 5.51 × 10−30 esu, respectively. Overall, the designed chromophores demonstrated significant NLO characteristics validating their potential as promising candidates for the optoelectronic applications.