鲁米诺-二甲亚砜-氢氧化钠体系化学发光机理的理论研究

用密度泛函理论(DFT) B3PW91/6-31G**方法研究了鲁米诺-二甲亚砜-氢氧化钠化学发光反应体系中反应物、中间体和产物的分子结构和振动频率, 用B3PW91/6-311＋G(3df,2p)方法获得反应能量以及用时间相关(Time Dependent, TD)的B3PW91/6-311＋G(3df, 2p)方法进行电子激发能态分析. 研究结果支持了下列化学发光反应通道: LH₂(¹A)＋OH^－ →LH₂•OH^－(¹A)→LH^－(¹A)→L^·－(²A)→TS₁(³A)→LO₂^2－(³A)→TS₂(³A)→AP^2－*(?³A)→AP^2－(X³A)＋hν, 最后即AP^2－*回到基态发光; 或AP^2－*(?³A)→AP^2－*(?¹A)→AP^2－(a¹A)＋hν, 即激发态势能面交叉后的单重态跃迁发光. 它们在可见光区域主要有400～460和500～530 nm的强吸收谱带, 与实验结果符合. 研究还表明, 质子化的鲁米诺能量将大幅度降低, 说明酸性溶液导致鲁米诺的反应活性降低, 从理论上解释了鲁米诺化学发光体系的溶液须呈碱性, pH值影响发光反应的实验事实.

Theoretical Study on the Chemiluminescence Mechanisms of Luminol-DMSO-NaOH System

Density functional theory (DFT) at B3PW91/6-31G** level was employed to investigate the structure and vibrational frequencies of reactants, intermediates, transition states and products in the chemiluminescence reaction of luminal-DMSO-NaOH system. Reaction enthalpies and the Gibbs free energies were calculated at B3PW91/6-311＋G(3df,2p) level with thermal corrections from the scaled frequencies of B3PW91/6-31G**. Electronic excitation states and energies of the key luminescence species AP^2－ were analysed by time-dependent DFT method at B3PW91/6-311＋G(3df,2p) level. This study, in the point of view of quantum theory, supported the chemiluminescence mechanisms of the reactions LH₂(¹A)＋OH^－→LH₂•OH^－(¹A)→LH^－(¹A)→ (²A)→TS₁(³A)→LO₂^2－ (³A)→TS₂(³A)→AP^2－*(?³A)→AP^2－(X³A)＋hν. In the last step, the potential energy hypersurface of the excited triplets AP^2－*(?³A) may also cross-link with that of the singlets AP^2－*(?¹A) and lead to chemiluminescence of singlets transitions AP^2－* (?³A)→AP^2－*(?¹A)→AP^2－(a¹A)＋hν. Two peaks of intense emissions in the ranges of 400～460 and 500～530 nm of visible lights were found. This has largely supported (with respect to the complexity of solvent effects) the experimental chemiluminescence spectra of luminal-DMSO-NaOH system. It has also been found that luminol will be greatly stabilized by protonation and therefore, the activity of luminol is extremely low in acidic solutions and the chemiluminescence intensity is influenced by acidity of solutions.