溶液环境中双光子分子荧光探针的光学性质和识别机理研究

Two-photon fluorescent microscopy has become a powerful tool for three-dimensional high-resolution and dark field imaging of substances in living cells. This technology relies strongly on the development of efficient two-photon fluorescent probes. At present, a large number of two-photon molecular fluorescent probes have been synthesized experimentally. However, the theoretical studies are mainly performed on isolated molecules. Since the probes usually work in solution, one should consider the solvent and aggregation effects on the optical properties of the probes. In this project, we focus on a series of rhodamine-based two-photon fluorescent probes. The geometries of the probes in solution will be obtained by employing molecular dynamics, and the structural changes of the probes caused by the inter-molecular interaction will be explored. The optical properties of the probes will be studied by means of quantum mechanics/molecular mechanics (QM/MM) method. Furthermore, the recognitional mechanisms of the probes will be investigated by analyzing the distributions of the frontier molecular orbitals and charge transfer of the molecular probes. With these studies, the relationships between the molecular structures and their optical properties will be established, and the influence of solution on the optical properties of the probes will be elucidated. This project will perfect the theoretical studies on two-photon molecular fluorescent probes and develop the method of describing the recognitional mechanisms, which provides theoretical references for the design and synthesis of high-efficient molecular fluorescent probes with strong two-photon absorption properties.

双光子荧光显微技术已成为新一代对活体细胞中的物质进行高分辨三维暗场成像的有力工具，该技术的发展迫切需要开发有效的双光子分子荧光探针。目前，实验上合成了大量的双光子分子荧光探针，而理论工作主要针对孤立的分子进行了研究。由于分子探针通常处在溶液环境中，因此需要考虑溶剂和聚集效应对探针光学性质的影响。本项目将以一系列基于罗丹明的双光子分子荧光探针作为研究对象，通过分子动力学方法得到溶液中分子探针的结构，探究分子之间的相互作用对探针结构的影响。在此基础上，采用量子力学/分子力学（QM/MM）方法研究分子探针的光学性质，并通过前线分子轨道分布及电荷转移情况，分析探针的识别机理，进一步揭示分子探针的结构与其光学性质之间的关系，阐明溶液环境对探针光学性质的影响。本项目将完善双光子分子荧光探针的理论研究，发展描述分子荧光探针识别机理的方法，为设计合成具有强双光子吸收性质的高效分子荧光探针提供理论参考。

双光子荧光显微技术具有近红外激发、暗场成像等一系列优势，目前已成为新一代对活细胞内部物质进行实时动态观测和检测的有力工具。在该项技术问世以后，迫切需要开发高效的双光子荧光探针。由于探针通常在凝聚态中发挥作用，因此需要考虑周围的溶剂环境对探针分子结构和性能的影响。本项目一方面采用第一性原理的方法，计算了一系列新型荧光探针分子，包括pH荧光探针、一氧化氮荧光探针和汞离子荧光探针在水溶液中的光学性质，结合分子轨道分布情况对探针的识别机理进行了探究，从理论上表征了荧光共振能量转移、跨键能量转移和光诱导电子转移过程。在此基础上，研究了连接基团、荧光团对探针分子性能和能量转移效率的影响，并评估了探针分子作为有效双光子荧光探针的可能性。另一方面采用分子对接和量子力学/分子力学相结合的方法，对靶向β淀粉样蛋白的荧光探针在蛋白中的可能结合位点进行了模拟，研究了不同位点处探针分子的构型及光学性质差异，计算了探针分子在与淀粉样蛋白结合前后的双光子吸收截面，揭示了微环境对探针结构及其单、双光子吸收谱和荧光光谱的影响。本项目发展了描述溶液和淀粉样蛋白环境中分子荧光探针光学性质及响应机制的理论方法，为人们理解环境对双光子分子荧光探针构型和光谱的影响提供可靠的参考。