利用组合宽带超快时间分辨荧光和瞬态吸收光谱实时探测核碱基及重要碱基衍生物的激发态光谱和动力学

Excited state dynamics of nucleobases represents a challenging and one of the key areas in photophysics, photochemistry, and photobiology. In this proposal, we will use a combined ultrafast broadband spectroscopy of time-resolved fluorescence and transient absorption in conjunction with steady-state method to perform a systematic study on selected nucleobases and a series of important rare bases and their derivatives in solvents of varying polarity and hydrogen bonding capacities. The broadband spectroscopic technique joint with ultrafast time-resolution serves as an ideal tool for revealing spectral signatures of the involved transient excited-states of the bases and selected rare bases and derivatives. The method also provides a direct way to monitor in real time temporal evolution of the excited-state spectra, thereby enables a direct probe of various nonradiative channels, including the ultrafast internal conversion, charge transfer, proton transfer, and intersystem crossing that can be possibly involved after the photo-excitation. Comparison of results obtained from the various selected systems will provide direct and explicit evidences for determining timescale and deciphering elementary steps of the excited state evolution; this will also allow accessing the structure-property relationship, in particular the effect of substitution on the excited state dynamics and role of solvent environment in affecting the spectra and dynamics of the deactivation channels. The successful implementation and accomplishment of this research will afford vitally important new experimental insights that should significantly enrich our knowledge on photo-excited nucleobases and their important derivatives, revealing at molecular level the origin of the remarkable photo-stability of the bases and the possible cause of their photo-damage. The results will enable to clarify the current controversies on the nature and dynamics of the base excited-states and provide hitherto unknown information to the excited states of some of the selected rare bases and base derivatives. It will also contribute to potential application of the base derivatives in areas such as gene regulation and anticancer drug development.

核碱基激发态动力学是目前光物理、光化学和光生物等研究领域中的热点和极具挑战性的课题。本项目拟利用组合宽带飞秒时间分辨荧光和瞬态吸收并结合稳态光谱，对所选碱基和一系列重要的稀有碱基及衍生物进行深入而细致的研究。通过直接捕捉其激发态的特征光谱，并实时跟踪其光谱随时间的变化，全面探测激发态的动态演化，确定各种可能去反应通道的相互转换和权重贡献。通过比较，揭示取代基位置、结构、及溶剂微环境等因素对激发态的影响，为明确指认激发态的电子性质，分辨激发态快速内转换、电荷传递、及系间窜越等过程提供直接的实验证据；以澄清目前对碱基激发态的疑问与争论；改善目前对有些所选稀有碱基和碱基衍生物激发态认知近乎空白的局面。提升人们对碱基及衍生物光物理、光化学性质的认识；为从分子层面上揭示碱基及重要衍生物的光稳定性、潜在光损伤及碱基衍生物在基因调控和抗肿瘤药物等方面的应用，提供重要的实验证据和基础。

本项目利用组合宽带飞秒时间分辨荧光和瞬态吸收另结合稳态光谱，对研究内容所涉及的一系列重要碱基及碱基衍生物进行了细致而深入的研究。实验获得了其激发态的特征光谱，并观测到其随时间的动态演化过程，为确定其激发态的辐射和非辐射去反应通道，及各通道的参与权重和相互转换，提供了直接的实验证据。另外，通过系统比较所选不同衍生物的激发态光谱和动力学，项目研究结果揭示出取代基的种类和位置及溶剂微环境等因素，对碱基的激发态的过程有不同和显著的影响。该取代基效应和溶剂效应为指认激发态的电子性质，及其非辐射失活通道，包括内转换、电荷传递 、系间窜越等，提供了关键的实验证据。研究结果澄清了目前对部分碱基衍生物激发态的争议；填补了目前对有些所选稀有碱基和碱基衍生物激发态认知的空白。丰富了人们对碱基及其衍生物光物理、光化学性质的理解；提升了在分子水平上，刻画该类重要生物分子的光稳定性及潜在光损伤的机理，对其在基因调控和抗肿瘤药物方面等的应用，具有重要意义。

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