We synthesized novel pyrido[2,3-b]pyrazin based heterocyclic compounds (4–7) and their chemical structures were ascertained by spectral techniques (NMR, FT-IR). Besides experimental investigation, density functional theory (DFT) computations with B3LYP/6-31G(d,p) level of theory were executed to obtain spectroscopic and electronic properties. Nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), UV-visible, vibrational analysis, natural bond orbitals (NBOs), transition density matrix (TDM) and density of states (DOS) analyses of molecules (4–7) were accomplished at B3LYP/6-31G (d,p) level. Global reactivity parameters (GRPs) were correlated with the band gap (E_gap) values; compound 7 with lower E_gap (3.444 eV), exhibited smaller value of hardness (1.722 eV) with greater softness value (0.290 eV⁻¹). The dipole moment (μ), average polarizability 〈α〉, first (β_tot) and second 〈γ〉 hyper-polarizabilities were calculated for compounds (4–7). Compound 7 showed less E_gap, highest absorption wavelength and remarkable NLO response. The highest 〈α〉, β_tot and 〈γ〉 values for compound 7 were observed as 3.90 × 10⁻²³, 15.6 × 10⁻³⁰ and 6.63 × 10⁻³⁵ esu, respectively. High NLO response revealed that pyrido[2,3-b]pyrazin based heterocyclic compounds had very remarkable contributions towards NLO technological applications. Further compounds (4–7) are utilized for the first time in electrochemical sensing of DNA, in vitro antioxidant and antiurease activity.

中文翻译：

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吡啶并[2,3-b]吡嗪衍生物的多组分合成：电化学DNA传感、非线性光学性质和生物活性

我们合成了新型吡啶并[2,3- b ]吡嗪基杂环化合物（4-7），并通过光谱技术（NMR、FT-IR）确定了它们的化学结构。除了实验研究之外，还执行了 B3LYP/6-31G(d,p) 理论水平的密度泛函理论 (DFT) 计算，以获得光谱和电子特性。分子的非线性光学 (NLO) 特性、前沿分子轨道 (FMO)、紫外-可见光、振动分析、自然键轨道 (NBO)、过渡密度矩阵 (TDM) 和态密度 (DOS) 分析 ( 4–7 )达到 B3LYP/6-31G (d,p) 级别。全局反应参数（GRP）与带隙（ E_间隙）值相关；化合物7具有较低的E_带隙（3.444 eV），表现出较小的硬度值（1.722 eV）和较大的软度值（0.290 eV ^-1）。计算了化合物 ( 4-7 )的偶极矩 ( μ )、平均极化率 < α >、第一 ( β _tot ) 和第二 < γ > 超极化率。化合物7表现出较小的E_间隙、最高的吸收波长和显着的NLO响应。化合物7的最高< α >、βtot和< γ >值分别为3.90×10 ^-23 _、 15.6×10 ^-30和6.63×10 ^-35 esu。高非线性光学响应表明吡啶并[2,3- b ]吡嗪基杂环化合物对非线性光学技术应用具有非常显着的贡献。其他化合物 ( 4-7 ) 首次用于 DNA 电化学传感、体外抗氧化和抗脲酶活性。