Influence of acceptors on the optical nonlinearity of 5H-4-oxa-1,6,9-trithia-cyclopenta[b]-as-indacene-based chromophores with a push–pull assembly: a DFT approach

Abstract

Herein, a series of compounds (TPD1–TPD6) having a D–π–A architecture was quantum chemically designed via the structural modulation of TPR. Quantum chemical calculations were employed to gain a comprehensive insight into the structural and optoelectronic properties of the designed molecules at the M06/6-311G(d,p) level. Interestingly, all the designed chromophores displayed narrow energy gaps (2.123–1.788 eV) and wider absorption spectra (λ_max = 833.619–719.709 nm) with a bathochromic shift in comparison to the reference compound (λ_max = 749.602 nm and E_gap = 3.177 eV). Further, E_gap values were utilized to evaluate global reactivity parameters (GRPs), which indicate that all the chromophores expressed higher softness (σ = 0.134–0.559 eV⁻¹) and lower hardness (η = 4.155–4.543 eV) values than the reference chromophore. Efficient charge transfer from donors towards acceptors was noted through FMOs, which was also supported by DOS and TDM analyses. Overall, the TPD3 derivative exhibited a remarkable reduction in the HOMO–LUMO band gap (1.788 eV) with a red shift as λ_max = 833.619 nm. Furthermore, it exhibited prominent linear and non-linear characteristics such as μ_total = 24.1731 D, 〈α〉 = 2.89 × 10⁻²² esu, and β_total = 7.24 × 10⁻²⁷ esu, among all derivatives. The above findings revealed that significant non-linear optical materials could be achieved through structural tailoring with studied efficient acceptors.