Photoinduced processes in nitrogen-substituted aromatic molecules and their dimers: A joint experimental and theoretical investigation .

在这个项目中，我们将研究含氮芳香分子的光化学和光物理，即多环芳香含氮碳氢化合物。该项目的一个特点是理论和实验的紧密结合。关于分离的分子和二聚体的数据允许与高级计算进行直接比较，并在没有环境影响的情况下深入了解分子的内在性质。自由喷流中的时间分辨光电离和光电子成像将得到量子经典动力学模拟的补充，这种方法允许与实验观测数据进行直接比较，如时延轨迹或光电子光谱。当使用时间分辨率约为4ps、带宽为15-20 cm-1的皮秒脉冲时，可以研究光动力学对沉积在分子中的过剩能量的依赖关系。虽然基本问题是我们研究的中心，但该程序也受到含氮分子与材料科学的相关性的激励。例如，碳原子被氮原子取代可以将以空穴导电为主的多环芳烃(PAH)转变为具有更好电子传导性的n型半导体。此外，PANH在天体化学中扮演着重要的角色，被认为是未知红外波段(UIB)的载体。在我们的研究计划中，我们将解决以下问题：a)通过引入一个N原子来改变PAH中激发电子态的顺序和性质。因此，我们将研究PANH中的电子结构和动力学随氮原子位置的变化。首先，我们将研究菲/菲并吡啶/苯并喹啉的序列，然后将我们的工作扩展到我们小组将合成的四苯和五苯衍生物。B)我们将研究氮取代对PANH二聚体结构的影响，特别是对准分子的形成的影响，这些二聚体在基态时相互作用弱，但在电子激发态时作用强烈。特别是氮杂四烯和氮杂五烯将是相关的，因为这两个生色团都被认为是单线态裂变(SF)的模型。在这一过程中，一个电子的激发会导致两个激子的形成，这可以提高使用合适材料的太阳能电池的效率。准分子信息可以被认为是迈向科学的第一步。C)与材料科学相关的杂环，如PTCDA和PBI，将通过激光脱附转移到气相中。随后，将从实验和理论上研究分子及其二聚体的光物理。

In this project, we will investigate the photochemistry and photophysics in aromatic molecules containing nitrogen, so-called PANH (polycyclic aromatic nitrogen-containing hydrocarbons). A characteristic of the project is the close cooperation between theory and experiment. Data on isolated molecules and dimers permit a direct comparison with high-level computations and give insight into the intrinsic molecular properties in the absence of environmental influence. Time-resolved photoionization and photoelectron imaging in a free jet will be complemented by quantum-classical dynamics simulations, an approach that permits the direct comparison with experimental observables, such as time-delay traces or photoelectron spectra. As picosecond pulses with a time-resolution of around 4 ps and a bandwidth of 15-20 cm-1 are employed, it is possible to investigate the dependence of the photodynamics on the excess energy deposited in the molecules.Although fundamental questions are in the center of our research, the program is also moti-vated by the relevance of nitrogen-containing molecules for materials science. For example, replacement of a carbon atom by a nitrogen can turn a predominantly hole-conducting polycyclic aromatic hydrocarbon (PAH) into a n-type semiconductor with improved electron conduction. Furthermore, PANH play an important role in astrochemistry and are considered as carriers of the unidentified infrared bands (UIB). In our research program we will address the following questions: a) the sequence and the character of excited electronic states in PAH is modified by the introduction of an N-atom. We will therefore investigate the electronic structure and dynamics in PANH as a function of the position of the nitrogen atom. Initially, we will study the sequence phenanthrene/ phenanthridine/ benzoquinoline and then extend our work to tetracene- and pentacene-derivatives that will be synthesized in our group. b) we will investigate the impact of the substitution by nitrogen on the structure of PANH di-mers and in particular on the formation of excimers, dimers that interact weakly in the ground state, but strongly in the electronically excited state. In particular aza-tetracenes and aza-pentacenes will be relevant, because both chromophore are considered as models for singlet fission (SF). In this process a one-electron excitation leads to the formation of two excitons, which can lead to an increased efficiency of solar cells using suitable materials. Excimer for-mation can be considered to be the first step towards SF. c) heterocycles with relevance for material science like PTCDA and PBI will be transferred into the gas phase by laser desorption. Subsequently, the photophysics of the molecules and their dimers will be investigated experimentally and theoretically.