Singlet exciton fission in polyacenes complexes: van der Waals dimers in the gas-phase and in helium nanodroplets

该项目的目的是实验研究的单重态激子裂变（SF）的聚并苯二聚体。1965年，SF首次被提出来解释结晶蒽的量子物理。近十年来，由于这一现象在有机光化学中应用的可能性，人们对它产生了浓厚的兴趣。文献中的估计表明，利用SF现象可以将单结太阳能电池的效率的Shockley-Queisser极限提高30%。为了优化SF过程，有必要了解其对结构和单体性质的依赖性，以及了解所涉及的基本过程的性质。在并四苯和并五苯及其衍生物中观察到最有效的SF。尽管积累了大量的实验材料，但要构建一个无争议的实验结果总结，并将实验与理论联合收割机结合起来，仍然是困难的。实验工作者的主要努力方向是研究多并苯的薄膜或多晶样品。这些薄膜的复杂形态是很难考虑到实验数据进行解释时，而且，此外，有效的方法，用于气相研究的电子物理学不能应用。在这个项目中，多并苯的货车范德华二聚体作为最简单的电子系统，包含两个多并苯分子进行了研究。这是在分子束条件下完成的，并作为氦纳米滴中分离的二聚体。氦纳米液滴中0.4K的非常低的温度将使我们能够识别由于吸收光谱的简化而导致的单线态激子的性质，以及使用光电子能谱识别所谓的暗态。我们将应用速度图成像的光电子提供的信息在一个非常详细的水平，在凝聚相不可访问的SF过程的物理学。利用飞秒泵浦-探测技术，在氦纳米液滴和分子束中对二聚体中SF过程的实时动力学进行了测量。弗赖堡团队拥有一套功能齐全的装置，用于生产掺杂分子的氦纳米液滴和一整套纳秒和飞秒激光器，以及在分子系统的光谱学和实时动力学方面的丰富经验。新西伯利亚研究组拥有脉冲分子束装置和速度图成像技术，并在货车德瓦耳斯分子复合物的光物理和光化学研究方面具有广泛的应用经验。在弗赖堡和新西伯利亚进行的实验研究期间，两个小组应该进行密切合作。弗赖堡和新西伯利亚集团已经进行了非常成功的合作，并联合出版了研究结果，其中应用了建议项目中使用的技术和设备。

The project aims at the experimental investigation of singlet exciton fission (SF) in dimers of polyacenes. SF was first suggested to explain photophysics in crystalline anthracene in 1965. Strong interest to this phenomenon appeared in the last ten years due to possibility of its application in organic photovoltaics. Estimations made in literature have shown that exploiting the SF phenomenon can increase the Shockley-Queisser limit of efficiency of single-junction solar cells by 30%. In order to optimize the SF process, it is necessary to understand its dependence on structure and monomer properties as well as to understand the nature of elementary processes involved. The most efficient SF was observed in tetracene and pentacene and their derivatives. In spite of the huge experimental material accumulated, it is still difficult to construct a non-controversial summary of experimental results and to combine experiment and theory. The main efforts of experimentalists are directed onto the studies of films or polycrystalline samples of polyacenes. The complicated morphology of these films is difficult to take into account when experimental data are interpreted, and, furthermore, efficient methods of photophysics as used in gas-phase studies cannot be applied. In this project van der Waals dimers of polyacenes are studied as the simplest electronic system containing two polyacene molecules. This is done at molecular beam conditions and as dimers isolated in helium nanodroplets. The very low temperature of 0.4K in helium nanodroplets will allow us to identify the nature of the singlet exciton due to simplification of the absorption spectra as well as to identify the so-called dark state with the use of photoelectron spectroscopy. We will apply velocity-map-imaging of photoelectrons providing information on the photophysics of SF processes at a very detailed level inaccessible in the condensed phase. Measurements of the real-time dynamics of SF process in dimers will be carried out with the use of femtosecond pump-probe techniques in both helium nanodroplets and molecular beams. The Freiburg group has a fully functional setup for producing helium nanodroplets doped with molecules and a complete set of nanosecond and femtosecond lasers, as well as extensive experience on the spectroscopy and real-time dynamics of molecular systems. The Novosibirsk group has a pulsed molecular beam setup combined with the velocity-map-imaging technique as well as extensive experience of its application for the studies of photophysics and photochemistry of van der Waals molecular complexes. Close collaboration of both groups is supposed to take place during the experimental studies carried out both in Freiburg and Novosibirsk. The Freiburg and Novosibirsk groups have already a very successful collaboration and joint publications with the results of the studies where techniques and equipment to be used in the suggested project were applied.