Herein, the novel D–π–A compounds (NDTD1-NDTD8) based on naphtho[1,2-b:5,6-b′]dithiophene were designed by modifying the donor and acceptor groups of NDTR reference. Density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were employed to analyze the geometrical, optoelectronic, and nonlinear optical (NLO) properties of these chromophores. After the structure optimization, various analyses were performed, such as the frontier molecular orbitals (FMOs), density of states (DOS), natural bond orbitals (NBOs), UV–Visible, transition density matrix (TDM), and non-linear optical (NLO) properties at the M06/6-311G(d,p) functional. The results showed that due to the presence of extended conjugation in the D–π–A derivatives, their energy gap (Egap) values were lowered as compared to the NDTR. The decreasing order of Egap for the studied compounds was obtained as: NDTR (2.659) > NDTD8 (2.232) > NDTD2 (2.184) > NDTD1 (2.097) > NDTD7 (2.061) > NDTD3 (2.002) > NDTD6 (1.928) > NDTD4 (1.901) > NDTD5 (1.811) in eV. The global reactivity parameters (GRPs) were calculated utilizing the Egap of these chromophores, showing their high chemical reactivity and stability. Moreover, the presence of hyper-conjugation and intramolecular attractions were demonstrated via the NBOs findings. Nevertheless, prominent charge transfer was observed in the studied chromophores displayed via their DOS and TDM plots. Interestingly, NDTD5 showed the minimal energy gap (1.811 eV) and highest bathochromic shift (λmax = 817.730 nm). From the NLO insights, all the studied compounds showed promising results, especially the NDTD5, which exhibited the highest average linear polarizability (⟨α⟩ = 3.809 × 10−22 esu), first hyper-polarizability (βtot = 3.414 × 10−27 esu), and second hyper-polarizability (γtot = 5.895 × 10−32 esu). Furthermore, it showed significant values for the simple harmonic generation (SHG) and electro-optic Pockel’s effect (EOPE) at 1907.21 nm, i.e., 4.21 × 10−27 and 10.4 × 10−27 esu, respectively. These outcomes showed that by utilizing strong donor and acceptor moieties in these D–π–A compounds, vital NLO materials are obtained for promising NLO applications.

Unveiling the impact of end-capped acceptor moieties on second and third nonlinear optical response of naphtho[1,2-b:5,6-b′]dithiophene-based derivatives

期刊论文
发表日期：

2026年1月3日

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Saba Abid,
Aiman Jabbar,
Zubaria Saeed,
Sadia Jamal,
Muhammad Haroon,
Saifullah Bullo,
Tansir Ahamad

摘要

Herein, the novel D–π–A compounds (NDTD1-NDTD8) based on naphtho[1,2-b:5,6-b′]dithiophene were designed by modifying the donor and acceptor groups of NDTR reference. Density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were employed to analyze the geometrical, optoelectronic, and nonlinear optical (NLO) properties of these chromophores. After the structure optimization, various analyses were performed, such as the frontier molecular orbitals (FMOs), density of states (DOS), natural bond orbitals (NBOs), UV–Visible, transition density matrix (TDM), and non-linear optical (NLO) properties at the M06/6-311G(d,p) functional. The results showed that due to the presence of extended conjugation in the D–π–A derivatives, their energy gap (E_gap) values were lowered as compared to the NDTR. The decreasing order of E_gap for the studied compounds was obtained as: NDTR (2.659) > NDTD8 (2.232) > NDTD2 (2.184) > NDTD1 (2.097) > NDTD7 (2.061) > NDTD3 (2.002) > NDTD6 (1.928) > NDTD4 (1.901) > NDTD5 (1.811) in eV. The global reactivity parameters (GRPs) were calculated utilizing the E_gap of these chromophores, showing their high chemical reactivity and stability. Moreover, the presence of hyper-conjugation and intramolecular attractions were demonstrated via the NBOs findings. Nevertheless, prominent charge transfer was observed in the studied chromophores displayed via their DOS and TDM plots. Interestingly, NDTD5 showed the minimal energy gap (1.811 eV) and highest bathochromic shift (λ_max = 817.730 nm). From the NLO insights, all the studied compounds showed promising results, especially the NDTD5, which exhibited the highest average linear polarizability (⟨α⟩ = 3.809 × 10⁻²² esu), first hyper-polarizability (β_tot = 3.414 × 10⁻²⁷ esu), and second hyper-polarizability (γ_tot = 5.895 × 10⁻³² esu). Furthermore, it showed significant values for the simple harmonic generation (SHG) and electro-optic Pockel’s effect (EOPE) at 1907.21 nm, i.e., 4.21 × 10⁻²⁷ and 10.4 × 10⁻²⁷ esu, respectively. These outcomes showed that by utilizing strong donor and acceptor moieties in these D–π–A compounds, vital NLO materials are obtained for promising NLO applications.