PhotonUp4Cat - Novel upconversion systems for photocatalysis with low energy photons

光化学上转换通过所谓的敏化三重态-三重态湮没机制，能够汇集两个可见光子的能量，以产生高能激发态。考虑到这种双光子机制可以由太阳或传统LED提供的极低的光强驱动，在特别温和的条件下，在催化、光生物(医学)和能量转换领域的一些应用变得可行，这一直吸引着许多科学家。从我们的探索性研究开始，我们打算带来两个与上转换相关的新概念。将有意义的光谱技术与制备和机械辐照实验相结合，应有助于克服固有的困难，从而为在这一竞争激烈的领域取得开创性成果铺平道路。该项目的第一部分涉及以前所未有的效率和光子能量(超过4 eV)将可见光转换为紫外光光子。这种对UVB光的上转换途径将用于污染物的降解和光催化应用。UVB光实际上不包含在陆地太阳光谱中，通常由对环境有害的灯产生。新型联苯基零化子将作为关键物种，在上转换过程中打破目前的单态能量记录，并从根本上研究和开发新的效应，例如关于溶剂依赖性的效应。第二部分致力于建立一种基于上转换的反应性控制方法，该方法能够简单地通过改变光强度在氧化和还原反应之间切换。设想的上转换系统由高度还原的敏化剂(在低强度下激活)组成，而激发的湮没单态只在较高的光强下产生，起到强烈的光氧化剂的作用。将这种反应性切换方法与几种不同的催化光氧化还原反应相结合是这一分项目的目标。该项目的预期结果将决定性地促进更可持续的光化学过程的发展，在这种过程中，可持续性是通过避免使用汞基紫外光源和依靠多种催化机制来解决的。

Photochemical upconversion via the so-called sensitized triplet-triplet annihilation mechanism is capable of pooling the energy of two visible photons in order to generate a highly energetic excited state. Given that this two-photon mechanism can be driven by very low light intensities, as provided by the sun or conventional LEDs, several applications in the fields of catalysis, photobiology (medicine) and energy conversion become feasible under particularly mild conditions, which keeps fascinating numerous scientists.Starting from our exploratory investigations, we intend to bring about two novel concepts related to upconversion. The combination of meaningful spectroscopic techniques with preparative as well as mechanistic irradiation experiments should facilitate overcoming inherent difficulties, thereby paving the way for groundbreaking results in this highly competitive field. The first part of this project is concerned with the conversion of visible light to UV photons with unprecedented efficiencies and photon energies (more than 4 eV). This upconversion access to UVB light, which is practically not contained in the terrestrial solar spectrum and typically produced by environmentally hazardous lamps, will be used for the degradation of pollutants and for photocatalysis applications. Novel biphenyl-based annihilators will act as key species to break the current singlet-state energy record in upconversion and to study and exploit fundamentally new effects, e.g., regarding solvent dependences. The second part is devoted to establishing an upconversion-based reactivity control approach, which enables to switch between oxidative and reductive reactivity simply by changing the light intensity. The envisaged upconversion systems consist of a highly reducing sensitizer (activated at low intensities), whereas the excited annihilator singlet, only produced at higher light intensities, acts as a strong photooxidant. Combining this reactivity switch methodology with several different catalytic photoredox reactions is the goal of this subproject.The expected results of this project will decisively contribute to the development of more sustainable photochemical processes, in which sustainability is addressed by avoiding mercury-based UV light sources and by relying on versatile catalytic mechanisms.