脱氧核糖核酸（DNA）激发态动力学的实时探测与超快宽带光谱研究

Excited state dynamics of deoxyribonucleic acid (DNA) represents a challenging area and one of the key research subjects in photophysics and photochemistry. In this proposal, we will use a combined ultrafast broadband spectroscopy of time-resolved fluorescence and transient absorption in conjunction with steady state methods to perform a systematic study on series of representative single-stranded and double-stranded DNA model compounds as well as natural DNAs. The broadband spectroscopic capacity joint with ultrafast time resolution serves as an ideal tool for revealing comprehensively spectral fingerprints of the involved transient excited state species. It also provides a direct way for real time monitoring temporal evolution of the excited state spectra, thereby enables a direct probe of various nonradiative channels, including excited state energy transfer, charge transfer, and proton transfer, that may possibly participate in the excited state deactivation. Comparison of results obtained for the selected systems will provide direct and explicit information for deciphering timescale and elementary steps of the excited state processes; allowing to access the structure-property relationship, in particular the sequence, composition, conformation and size dependence of the excited state dynamics, as well as to evaluate the role of inter-base interactions (i.e., stacking and pairing) in modulating dynamics of the varied decay channels. The successful implementation and accomplishment of this research will afford vitally important new experimental insights that should significantly enrich our knowledge of photo-excited DNAs, revealing at molecular level the origin of DNA photostability and possible cause of photodamage. The results of proposed work will enable to elucidate the current controversies on the nature and dynamics of DNA excited-states and also contribute to potential application of DNA in the area of functional biomaterials.

脱氧核糖核酸(DNA)激发态动力学是目前光物理、光化学研究领域中的热点和极具挑战性的课题。本项目拟结合超快宽带时间分辨荧光和超快宽带瞬态吸收并配合稳态光谱，对一系列具代表性的DNA模型聚体及天然DNA进行深入而系统的研究。通过直接捕捉激发态的特征指纹光谱，实时跟踪激发态光谱随时间的变化, 全面探测激发态的动态演化过程, 以确定各种可能弛豫通道的相互转换及对整个动力学过程的权重贡献; 通过比较，阐明碱基堆积、配对、DNA构型、组成、长度等因素对激发态的影响, 为指认激发态电子性质, 揭示激发态能量传递、电荷传递、质子传递及DNA结构对这些过程的调控与影响提供直接的实验证据，以澄清目前对DNA激发态的争论, 并丰富人们对DNA光物理及光化学过程的认识, 为从分子层面上揭示DNA的光稳定性、潜在光损伤及DNA在材料等方面的实际应用，提供直接的实验证据和坚实的基础。

了解核酸激发态动力学是当前光物理、光化学研究领域中的热点和极具挑战性的课题。在前期工作的基础上，本项目的执行总体按计划书预设的研究内容、研究方法和研究步骤进行，实现了预设的研究目标。具体而言，包括依研究方案，利用所选的各种稳态光谱和组合时间分辨荧光和瞬态吸收的光谱方法，研究不同长度和组成的单链核酸、双链核酸及天然核酸的激发态光谱和动力学，进而获得其激发态的指纹光谱和特征动力学常数，并以此作为直接的实验证据，以揭示核酸激发态的去反应通道及所涉各通道间的动态竞争及相互转换，并确定影响激发态路径的结构因素，及碱基组成、碱基各种相互作用和微环境因素等对核酸及相关体系激发态过程，尤其是能量传递、电子传递和质子传递等重要光物理和光化学过程的影响和调控。项目的研究和探索得出了一套有效的实验方法和数据分析手段，以直接追踪和探测极具挑战性的核酸激发态的复杂光谱性质和动态行为。此外，项目的执行亦包括对相关体系，如胞嘧啶碱基及重要衍生物；与光保护、光损伤密切相关的、具光致电子传递性质的紫外防护分子；及非常规胞嘧啶核酸四链体结构的激发态光谱和非辐射动力学的探索和研究。项目的研究具开拓性，并取得了重要的阶段性研究成果，在相关领域国际核心期刊发表论文5篇，培养已毕业研究生两名，在站博士后研究员一名，项目主持人和团队成员多次参加国际和国内相关学科的学术会议，并做口头或邀请报告。鉴于核酸在生物和纳米材料等方面的重要性，项目的研究结果和所得数据，对从分子层面上诠释目前了解甚少的核酸光物理、光化学性质、光诱导的核酸变异，及拓展核酸在分子器件等方面的应用，皆具有重要的意义。