Abstract
The structural alteration with pi-linkers was used to design a donor-acceptor type series of 2,2'-(pyrimidine-4,6-diyl)bis(2,3-dihydro-1,3-benzothiazole) (PB)-based chromophores (AH1-AH7) to exploit the adjustments in their optical characteristics. To investigate the electronic geometries, absorption wavelengths, charge transfer processes, and the effect of structural alterations on nonlinear optical (NLO) characteristics, density functional theory (DFT) simulations have been used. During the UV-visible study, several long-range and range separated functionals like B3LYP, CAM-B3LYP, B97XD, and APFD with the 6-311G+ (d,p) basis set were used to select the efficient level at DFT. As a response, UV-vis data indicated an intriguing consistency at the B3LYP level across experimental and TD-DFT-based values of PB. All the designed molecules had a smaller energy band gap (0.84-3.67 eV) and wide absorption spectra inside the visible region. Natural bond orbital (NBO) results indicated a significant push-pull operation, with donors and pi-conjugates exhibiting positive values and most acceptors exhibiting the minimum values. Electronic transformations between electron donors to acceptor moiety, Trifluoromethyl (TFM) via pi-conjugated linkers were shown to have a superior linear (<)alpha> and nonlinear (beta(total)) NLO values of 306-474 and 40-230 Debye-Angstrom(-1) respectively. When chromophores with one phenyl pi-linker were compared to those with the two pi-linkers, the chromophores with the higher t-linker showed increased hyperpolarizability. The highest second-order hyperpolarizability (beta) was found to be 230.11 Debye-Angstrom(-1) which was about five times higher than urea (standard). This research has shown that by manipulating the kind of pi-spacers, novel metal-free NLO compounds may be created, which might be used for high-tech NLO purposes.