Structural, electronic, NLO, UV-Vis, and vibrational studies of Schiff base liquid crystals TBnA (n = 4-8) via DFT/TD-DFT with alkyl-chain modulation.

contextThe unique combination of fluidity like liquids and directional organization like solids in liquid crystals (LCs) gives rise to their special properties. This article presents a theoretical study on Schiff's base thermotropic LC, tetraphthalylidene-bis-p-n-alkylaniline (TBnA) homologous series (n = 4-8). The aim is to understand the relationship between the molecular design and physical properties with varying alkyl chain length. Optimized molecular geometries, electronic, thermodynamic, and nonlinear optical (NLO) parameters are calculated theoretically. The polarizability of the LCs is high, and the first-order hyperpolarizability is not zero, which makes them a good candidate for NLO applications. A consistent 3.55 eV energy gap across a series indicates a uniform electronic structure, positioning them as promising candidates for optoelectronics applications, and chemically stable and tunable wide band gap requiring fields. UV-Vis absorption spectra calculated using TD-DFT explored oscillator strength and involved electronic transitions. Raman and IR modes aid in characterizing functional groups and phase transition markers. The results reveal valuable insights into the electronic distribution, stability, and excitation of TBnA, providing a theoretical foundation for the design and optimization of LCs for advanced optoelectronic applications.

methodsThe widely accepted DFT with B3LYP functional is used for the simulation along with 6-311G(d,p) basis set in Gaussian 09 software. All the frontier orbitals, thermodynamic, NLO, and spectroscopic studies are performed at the same computational level. Time-dependent DFT (TDDFT) and the multiwfn software are used for the UV-Vis spectra. Vibrational spectroscopy assignment analyses are done using VEDA software and GaussView animation.