以芘(Pyrene)为荧光母核的PID荧光探针检测Hg²⁺的机制研究

Elucidation of Hg²⁺ Sensing Mechanism for a Pyrene-Based PID Fluorescent Probe

摘要: 为阐明PID荧光探针对重金属离子Hg²⁺的特异性荧光“关–开”识别微观机制，本研究采用B3LYP与长程校正泛函CAM-B3LYP两套密度泛函理论方案的密度泛函理论(DFT)、含时密度泛函理论(TD-DFT)开展量子化学计算，结合平均局部离子化能(ALIE)、态密度(DOS)、电子密度差异、原子电荷转移贡献热图、振子强度等多维度电子结构表征手段，系统解析PID探针与Hg²⁺反应前后分子轨道、电子转移及光激发特性变化。ALIE分析结果证实，探针分子中C=C双键区域电子电离能最低，是Hg²⁺发生特异性配位及加成反应的核心活性位点；未结合Hg²⁺时，PID探针存在分子内电荷转移(ICT)效应，S₀→S₁振子强度极低，荧光完全猝灭；与Hg²⁺发生特异性反应后，分子共轭骨架重构，前线轨道同步局域于荧光母核，激发模式由分子内电荷转移(ICT)转变为局域激发(LE)，辐射跃迁概率大幅提升，体系释放明亮蓝色荧光。本研究从电子行为层面完整揭示PID探针识别Hg²⁺的构效关系，为重金属离子响应型荧光探针分子设计、识别位点优化提供理论支撑与标准化计算分析思路。

Abstract: To clarify the microscopic “off-on” fluorescence recognition mechanism of PID fluorescent probe for heavy metal ion Hg²⁺, two computational schemes including conventional B3LYP and long-range corrected CAM-B3LYP functionals were adopted for DFT and TD-DFT quantum chemical calculations in this work. Multiple electronic structure characterization methods including average local ionization energy (ALIE), density of states (DOS), electron density difference, atomic charge transfer contribution heat map and oscillator strength were combined to systematically analyze the changes of molecular orbitals, electron transfer and photoexcitation characteristics of PID probe before and after reaction with Hg²⁺. ALIE analysis verified that the C=C double bond region of the probe possessed the lowest ionization energy, which served as the core active site for specific coordination/addition reaction with Hg²⁺. In the absence of Hg²⁺, the PID probe exhibited intramolecular charge transfer (ICT) effect with extremely low oscillator strength of S₀→S₁ transition, leading to complete fluorescence quenching. After specific reaction with Hg²⁺, the molecular conjugated skeleton was reconstructed, and frontier orbitals were localized on the fluorophore core simultaneously. The excitation mode transformed from intramolecular charge transfer (ICT) to local excitation (LE), which greatly increased the probability of radiative transition and emitted bright blue fluorescence. This study fully revealed the structure-property relationship of PID probe for Hg²⁺ recognition from the perspective of electronic behavior, and provided theoretical support and standardized computational analysis strategy for molecular design and recognition site optimization of heavy metal ion responsive fluorescent probes.