Exploring key electronic and non-linear optical amplitute with bilateral intramolecular charge transfer into thieno[3,2-b]thiophene-based compounds: a DFT approach

Abstract

Organic molecules are considered important NLO materials in the modern age because of their potential optoelectronic features. Therefore, a series of organic molecules (DBTD1–DBTD7) with a D–π–A architecture was designed from the reference compound (DBTR) by structurally tailoring it with effective donors and making significant modifications to the π-spacers. All derivatives and references were initially optimized at the M06 functional with a 6-311G(d,p) basis set. Furthermore, the optimized structures (DBTR and DBTD1–DBTD7) were used to determine the density of states (DOS), frontier molecular orbitals (FMOs), natural bond orbital (NBO), UV-Visible, transition density matrix (TDM) analyses, and the most significant NLO properties. Among the compounds, DBTD4 had the smallest band gap (2.882 eV) which was further supported by DOS analysis. The global reactivity parameters were also related to the HOMO–LUMO band gap, where the compound with the lowest band gap showed a lower hardness value and higher softness value. NBO analysis was used to explain the molecular stability and hyperconjugation. DBTD4 and DBTD5 demonstrated comparable low bandgaps with the highest comparable NLO parameter values. However, we also observed efficient NLO characteristics for DBTD6 and DBTD7. The highest μ_tot value is observed in DBTD6 as 10.362 D, whereas the highest α_tot (1.48 × 10⁻²² and 1.47 × 10⁻²² esu) is observed in DBTD6 and DBTD7. Further, β_tot (6.68 × 10⁻²⁸ and 6.23 × 10⁻²⁸ esu) in DBTD4 and DBTD5 and γ_tot (6.20 × 10⁻³³ and 6.59 × 10⁻³³ esu) values are observed in DBTD5 and DBTD6. To acquire favorable NLO responses in molecules, structural modelling utilizing efficient donor units played significant role. Thus, current research insights encourage researches to develop efficient NLO materials for optoelectronic applications.