荧光素类探针分子发光机理的研究

Since fluorescein was synthesized for the first time in 1871, it has been used widely for labeling and sensing biomolecules.For a long period of time, a large number of fluorescein-based fluorescence probes have been developed, however, studies on the luminescence mechanism of fluorescein derivatives have been seldom been reported. Nowdays it is generally accepted that photo-induced electron transfer is the major pathway for quenching the fluorescence of the fluorescein derivatives. Recently, we used the TDDFT and RICC2 to check the validity of the PET mechanism, the calculated results indicated that the energy of the charge transfer state is clearly higher than that of the bright state, which can not be used to quench fluorescence, this is in contrast with the PET mechanism. Thus, further studies are needed to investigate the luminescence mechanism of fluorescein derivatives. This project will use the ultrafast time-resolved spectroscopy and quantum chemistry calculations to study the luminescence machanism of fluorescein derivatives, the objectives of this project are to find the major pathway for quenching the fluorescence of the fluorescein derivatives from experimental studies, and to illustrate the effect of molecular stuctrue on the fluorescence quantum yield of fluorescein derivatives using the theoretical methods.

荧光素自1871年首次被合成以来，便由于其良好的性能而被广泛用于标记和检测生物分子。长期以来，人们以荧光素为底物，设计并合成出了大量的荧光素类衍生物，但是，对荧光素类衍生物发光机理的研究则比较少。目前人们普遍认为，淬灭荧光素类衍生物荧光的主要途径是光诱导的电子转移（PET）。最近，我们利用TDDFT和RICC2方法对PET机理进行了检验，结果发现，对荧光素类衍生物而言，发生PET之后所形成的电荷转移态的能量明显高于发光态，无法淬灭荧光，这与PET机理相矛盾。理论计算与实验预测相矛盾的事实促使我们需要对荧光素类衍生物分子的发光机理展开进一步研究。本项目拟利用超快时间分辨光谱与激发态量子化学相结合的方式，对荧光素类衍生物的发光机理开展研究，期望从实验上找出淬灭荧光素类衍生物荧光的主要途径，并从理论上阐明分子结构对荧光素类衍生物荧光量子产率的影响。

荧光素由于其在水溶液中高的发光效率以及合适的吸收和发射波长，而被广泛用于新型荧光探针的设计与合成。对荧光素以及其衍生物的发光机理进行研究，有助于人们更加合理、快速的设计出性能良好的荧光探针。通过本项目的实施，我们发现影响其发光效率的主要因素是分子构型的改变而引起的内转换效率的改变，而不是人们之前所认为的光致电子转移机理。我们发现溶质溶剂间分子氢键的强度也是影响其内转换效率的一个主要因素。我们还对一系列相关的荧光探针分子的发光机理进行了实验和理论研究，给出了其详细的发光机理，有些探针分子的发光机理实验和理论结果相一致，而对有些探针分子，理论计算推翻了实验所推测的机理并给出了新的更合理的解释，这些研究成果充分说明了实验推测的发光机理必须经过理论计算的检验和验证才能确保其正确性和合理性。我们的研究成果为人们设计和合成新的荧光探针分子提供了理论依据。