High resolution spectroscopy of directly excited triplet and singlet states

有机分子的长寿命三重态是决定其光物理和光化学性质的重要因素。作为开壳层体系，它们作为各自的闭壳层单重态具有更高的反应性。在它们的长寿命期间，它们可以通过多次碰撞克服甚至很高的反应障碍。除了光化学方面，三重态（和单重态）的几何形状的知识是重要的解释系统间的交叉，三重态-三重态湮灭和理解的基本过程中的有机发光二极管（OLED）。尽管它们非常重要，但处于这些状态的分子的结构大多是未知的。结构在这里被定义为键长和键角，它们决定了分子在各自状态下的三维外观。这主要是由于经典的结构测定方法（NMR、X射线衍射、中子散射）仅适用于处于其电子基态的分子，所述电子基态是闭合壳层单重态。电子激发的光谱方法原则上可以得到结构信息，但到目前为止，仅限于激发单重态。这种限制是由单重态-三重态跃迁的小激发截面引起的。在我们的小组中，我们获得了确定电子激发单重态分子结构和偶极矩的经验。特别是，发明的进化策略的分子参数的旋转分辨的电子光谱的自动拟合促进了调查的大和弱荧光分子。旋转分辨率是确定分子在各个电子态下的转动惯量的关键，从转动惯量可以推断出分子的结构。在与莱昂的列奥纳多阿尔瓦雷斯小组的合作中，我们的目标是克服对单重态的限制，并记录从基态直接激发后分子在三重态的旋转分辨电子光谱。该技术包括观察几何形状的改变，这使得可以在更长的时间内检测磷光。现代单模环形染料激光器的更高激光功率允许更高的激发速率。光谱的评估将使用进化算法使用我们的拟合程序的更新版本进行，这将有助于确定额外的分子参数，如自旋-自旋和自旋-旋转耦合常数。

Photophysics and Photochemistry of organic molecules are mainly determined by their long-lived triplet states. As open shell systems, they have a higher reactivity as the respective closed shell singlet states. During their long life times, they can surmount even high reaction barriers through multiple collisions. Apart from photochemical aspects, the knowledge of triplet (and singlet) state geometries is important for interpretation of intersystem crossing, for triplet-triplet annihilation and for the understanding of basic processes in of organic light emitting diodes (OLEDs). Despite their great importance, the structures of the molecules in these states are mostly unknown. Structures are defined here as bond lengths and bond angles, which determine the three-dimensional appearance of a molecule in the respective state. This is mainly due to the fact that classical structure determining methods (NMR, X-ray diffraction, neutron scattering) are applicable only to molecules in their electronic ground state, which are closed shell singlet states. Spectroscopic methods with electronic excitation can yield structural information in principle, but are, up to now, restricted to excited singlet states. This restriction is caused by the small excitation cross sections of singlet-triplet transitions. In our groups, we gained experience in the determination of structures and dipole moments of molecules in electronically excited singlet states. Particularly, the invention of evolutionary strategies for the automated fit of molecular parameters to the rotationally resolved electronic spectra facilitated the investigation of large and of weakly fluorescing molecules. Rotational resolution is the key to the moments of inertia of the molecules in the respective electronic states, from which the structures can be deduced. In this cooperation with the group of Leonardo Alvarez in León we aim to surmount the restriction to singlet states and record rotationally resolved electronic spectra of molecules in their triplet states after direct excitation from the ground state. The technique comprises a change of the observation geometry, which makes in possible to detect the phosphorescence for a longer time. The higher laser power of modern single mode ring-dye lasers allows for higher excitation rates. The evaluation of the spectra will be performed with an updated version of our fitting program using evolutionary algorithms, what will facilitate the determination of additional molecular parameters like spin-spin and spin-rotation coupling constants.