用于监控过氧化氮的近红外荧光探针的光物理性质及PET机理

含有机硒的七甲川菁染料是基于光诱导电子转移(PET)的近红外(IR)荧光探针, 能在生理条件下高灵敏、高选择性地监控过氧化氮. 本文应用含时密度泛函理论(TD-DFT)计算方法研究其光物理性质和PET机理.结果表明, 在激发态, 荧光母体发生最高占有分子轨道(HOMO)到最低非占有分子轨道(LUMO)的电子跃迁, 识别基团上的HOMO轨道能级提高到荧光母体的单电子占据的HOMO轨道能级之上, 并向其转移一个电子, 使激发态电子回落过程受阻而导致荧光部分淬灭. 硒被氧化后, 识别基团上的HOMO轨道能级降低, PET过程被阻断, 荧光发射恢复. 研究进一步证明, PET效应来自于识别基团上苯胺N原子的p电子, 它的电子转移能力受到其对位苯硒基的氧化-还原状态的影响, 产生了荧光信号的“开-关”作用.

Photophysical Properties and Photoinduced Electron Transfer Mechanism in a Near-IR Fluorescent Probe for Monitoring Peroxynitrite

A heptamethine cyanine dye containing an organoselenium functional group is a near-IR fluorescent probe that operates based on photoinduced electron transfer (PET). This probe can be used for highly sensitive and selective monitoring of peroxynitrite under physiological conditions. In this paper, the photophysical properties and PET mechanism of the probe molecule were investigated by time-dependent density functional theory (TD-DFT) calculations. The results indicated that the excitation in the fluorophore involves an electron transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). The HOMO level of the recognizer moiety increased in energy above that of the HOMO occupied with a single electron of the fluorophore, leading to transfer of one electron to the heptamethine cyanine moiety, which quenched the fluorescence emission. After the Se moiety was oxidized, the HOMO level of the recognizer moiety decreased in energy, the PET process was prevented, and the fluorescence emission was recovered. It was further proposed that the PET was contributed to by the p electron of the nitrogen atom in the aniline moiety of the probe. The PET efficiency is regulated by the oxidation and reduction events of the organoselenium moiety, resulting in“on-off”fluorescence emission.