具有小单线态/三线态能级差的湮灭剂制备与弱光上转换增强机理研究

Low-power upconversion (UC) can convert long-wavelength light (such as sun light) to short-wavelength light based on triplet-triplet annihilation (TTA) mechanism, which show many potential applications in the field of solar cell, production hydrogen and photocatalysis. However, the materials for infrared light upconversion so for possess very low efficiency (< 6%，100 mW/cm2) that is one of the main bottlenecks of UC application.. The TTA-UC phenomenon undergoes a series of quantum processes that involve a bimolecular system containing a sensitizer and anacceptor. Firstly, the sensitizer harvests the excitation energy toward its triplet excited state by intersystem crossing (ISC). Secondly, the sensitizer shifts its triplet energy to the acceptor, which is called triplet-triplet energy transfer (TTT). Thirdly, two excited triplet acceptors encounter each other and produce one excited singlet state (S1) and one ground state (S0), which is called triplet–triplet annihilation (TTA). Lastly, the S1 state decays from the excited state to the ground state and irradiates the upconversion fluorescence. Since the upconversion efficiency is dependent of sensitizer and acceptor (i.e., annihilators), study on various new efficient sensitizer and annihilators become hot project so far.. In this project, we first apply the concept “thermally activated delayed fluorescence (TADF)” to develop the new-type of annihilators that show rigid/ high steric hindrance polaron and decreased overlap between the HOMO and LUMO in order to obtain the annihilators with small singlet-triplet energy gap. Thus, the objects in this project are as follows:. 1) to synthesize a series of new annihilators with rigid/ high steric hindrance polaron;. 2) to investigate the influence of annihilator’ structure upon small singlet-triplet energy gap;. 3) to study the transition approach and decay of reverse intersystem crossing (RISC) and the thermally activated delayed fluorescence (TADF);. 4) to understand how to collaboratively increased the triplet-triplet annihilation upconversion by the thermally activated delayed fluorescence (TADF);. 5) to elucidate the new mechanism that 55.6% spin quintets and 33.3% spin triplets can also be annihilated to the singlet (S1) via RISC pathway.. In sum, our aim is to develop a new generation of high efficient annihilators for the purpose of infrared light low-power upconversion application.

弱光上转换有望将太阳光谱中近红外光转化为所需要的短波长的光，在太阳能电池、太阳能产氢、光催化等新能源开发中具有重要应用前景。然而，上转换效率甚低是遏制其应用的主要瓶颈。. 本项目首次将热激活延迟荧光概念用于弱光上转换体系湮灭剂的研究，研发新一代小单线态/三线态能级差湮灭剂，探索热激活延迟荧光协同增强弱光上转换的新机制。阐明湮灭剂结构与降低其单线态/三线态能级差以及抑制其非辐射衰变常数通道的内在规律；研究将55.6%的自旋五重态激子和33.3%的自旋三重态激子高效转化为激发单线态，并沿辐射通道衰变的内在机制；在研究“湮灭剂分子结构－反系间窜越－热激活延迟荧光－红外光上转换效率 ”构效关系基础上，建立协同增强弱光上转换的新机理，为弱光如太阳光上转换的应用提供重要的理论依据和实验依据。

弱光“上转换”是指在弱光场中，通过长波长的光激发获得短波长光的一种现象，在能源、显示、生命科学和检测防伪等领域具有潜在应用价值。本项目围绕“弱光上转换机理和性能”，展开新材料构效关系研究：设计制备一类9,10-二取代苯基蒽衍生物。研究表明，小的单线态-三线态能级差（EST）和平面构型可有效提高上转换效率，为高效三线态湮灭剂分子设计提供了新的思路。成果发表在Dyes Pigments期刊。设计制备一类全色发光上转换湮灭分子，在绿光激发下获得稳定高效白光发射，效率高达8.8%。醛基微扰效应是其全色发光的结构原因。成果发表J. Mater. Chem. C(Comm.) ，被选为封底文章。报道了氧杂蒽衍生物的单光子热带吸收上转换（OPA-UC）。发现大的分子内电荷转移（ICT）和高的分子内旋转受阻(RIR)有利于提高OPA-UC效率，最大上转换效率7.56%，红-转-黄反斯托克斯位移0.28eV。成果2020年发表在Dyes Pigments期刊。首次通过级联单光子热带吸收机制（OPA）和三线态湮灭上转换（TTA-UC）机制，获得了反斯托克斯位移达0.99 eV的红-转-蓝上转换，净效率达1.23 %。本工作对研发新的上转换机理具有一定的启发作用。成果已投稿至J. Mater. Chem. C(Comm.)。将天然萜烯作为TTA-UC体系的新介质，以解决三线态上转换绝氧瓶颈问题，成果发表在PCCP期刊，被选为封面文章。将乳液上转换体系包裹于水凝胶体系内获得了固态的上转换。发现水凝剂体系包裹的上转换微乳液具有较高的发光效率且随温度的升高而提升，直至70oC 达到极值。成果发表在J. Phys. Chem. C期刊。设计制备了多层空间结构的钯酞菁，研究表明多层酞菁钯有利于三线态能量转移，使得上转换效率提高。成果发表在 J. Phys. Chem. C期刊。