基于分子内共振能量转移的宽谱带吸收有机三重态光敏剂的制备和若干基本光物理问题的研究

Triplet photosensitizers are widely used in photocatalysis, photodynamic therapy, and more recently the triplet-triplet-annihilation (TTA) upconversion. Conventional triplet photosensitizers are based on mono-chromophore profile, as a result, there is only one major absorption band in visible spectral region, which is detrimental for applications where broadband excitation light source was used (e.g. solar light). Moreover, it is difficult to modify the molecular structures of the traditional photosensitizers such as porphyrin or aromatic ketones.Another major challenge is how to design heavy atom-free triplet photosensitizers, because in this case the intersystem crossing (ISC) is unpredictable. In order to adress these challenges,this project will desi broadband absorbing triplet photosensitizers based on resonance energy transfer (RET) effect between energy donor and acceptor (also as the 'spin converter'). Both the enery donor and the energy acceptor give strong absorption in visible spectral region, but at different wavelength, thus broadband absorption can be achived. Fundamental photophysical processes concerning these new triplet photosensitizers will be studied. First, different energy donors and acceptors, such as Rhodamine, fluorescein, and naphthalenediimde (NDI) will be studied for construction of this dyad type of triplet photosensitizers. Proper combination of the energy donor and acceptor and the effect of the rigidity of the linkers between the energy donor and acceptor will be also studied.All these molecular structural features impose influence on the property of triplet photosensitizers.All the factors will be optimized to minimize the photo-induced intramolecular electron transfer (ET), and to maximize the intramolecular energy transfer (EnT). EnT is beneficial for production of triplet excited state, but the ET is not. Second, pH-activatable triplet photosensitizers will be prepared by using pH-responsive moiety, such as Rhodamine, as energy donor or energy acceptor. As a result, the ISC of the spin converter part of the triplet photosensitizer will be perturbed by RET, which is controlable by external stimuli, such as variation of the pH of the solution. We will study different energy donor, energy acceptor for optimize the competition of between the ISC and the RET, to maximize the OFF-ON switching effect of the triplet photosensitizers, by variation of the pH of the solution. We have carried out preliminary study (some of the RET triplet photosensitizers designed in this research proposal have been prepared and some of the photophysical properties have been studied), the results are promising. With implementation of this research project, new insights into the RET based broadband absorbing triplet photosensitizers will be gained, which are very useful for desiging new triplet photosensitizers and for the application of these compounds in photocatalysis, photodynamic theraputic reagents and TTA upconversion.

为了克服现有三重态光敏剂只含单一吸光基团而导致的吸收谱带窄、不能有效利用宽谱带激发光（如太阳光），以及分子结构不易修饰等缺点，本项目将设计、制备新型的、含两个不同的吸光基团以构成分子内共振能量转移（RET）、并利用分子内自旋转换单元的新型有机三重态光敏剂，以达到宽谱带吸收、分子结构可灵活修饰的目的，并确保系间窜越的发生。将研究若干基本光物理问题，比如，选择合适的能量给体、受体，以减少分子内电子转移与能量转移的竞争，从而提高三重激发态的生成效率。将使用罗丹明、荧光素、萘酰二亚胺等做为能量给体、受体，使用三聚氯氰、烷基链等具有不同刚性的连接基团，研究这些分子结构因素对电子转移、能量转移的影响；其次，计划在RET三重态光敏剂分子中引入对外部刺激具有响应性的基团做能量受体或给体，比如罗丹明（在中性、碱性条件呈现两种结构，其光物理性质不同），实现利用外部条件对三重态的产生进行'开关'形式的调控。

为了克服现有三重态光敏剂只含单一吸光基团而导致的吸收谱带窄、不能有效利用宽谱带激发光（如太阳光），以及分子结构不易修饰等缺点，本项目设计制备了新型的、含两个不同的吸光基团以构成分子内共振能量转移（RET）、并利用分子内自旋转换单元的新型有机三重态光敏剂，实现了宽谱带吸收、分子结构可灵活修饰的目的，并确保了高效系间窜越的发生。通过选择合适的能量给体、受体，构建了具有分子内能量转移的多元分子体系，利用纳秒和飞秒时间分辨光谱，对分子内能量转移和电子转移过程进行了研究，测定了各光物理过程的速率常数；同时将合成的具有宽谱带吸收的新型光敏剂用于了光动力治疗（PDT）、光催化等领域。此外，在RET三重态光敏剂分子中引入对外部刺激具有响应性的基团做能量受体或给体，比如罗丹明（在中性、碱性条件呈现两种结构，其光物理性质不同），实现了利用外部条件对三重态的产生进行'开关'形式的调控，并将其用于光动力治疗、三重态湮灭上转换中。通过本项目的实施，对相关的多发色团分子的基本光物理过程的规律进行了研究，为进一步将此新结构类型的分子用于PDT等领域，奠定了基础。共在SCI检索的化学期刊发表通讯作者论文50余篇（JACS, Chem. Commun., Chem.-Eur. J., J. Phys. Chem. C等期刊），形成了基本完整的知识体系；在项目实施期间，项目负责人连续四年被列入Elsevier中国高被引用学者榜单；2016年获得辽宁省科学技术奖励一等奖（自然科学类）；培养了7名博士毕业生、3名硕士毕业生。

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