Electronic structure of protonated aromatic and chiral molecules

本项目旨在通过激光光谱、质谱和量子化学表征选定尺寸的质子化芳香分子及其在气相分离的簇，以确定它们在基态和激发态的几何和电子结构。目标分子是质子化（多环）芳烃分子，范围从苯到冠烯，以及简单的衍生物和非极性和极性配体（稀有气体原子，氮，水）的簇，以模拟疏水和亲水溶剂化。所考虑的分子在有机化学、燃烧、生物化学和天体化学中具有基本的相关性。质子化对电子和几何结构的影响是巨大的，因为它降低了芳族pi-电子系统的对称性和芳香性，并产生了低洼的电荷转移态。因此，质子化在很大程度上改变了这些芳香分子的光化学和光物理性质，这在实验和理论上都是很大程度上未被探索的。此外，与溶剂分子的相互作用在质子化和电子激发下发生了巨大的变化，并且将特别关注微水合团簇中质子与溶剂之间的转移。要解决的基本问题包括能量、结构、电荷分布、分子轨道、质子化位点和质子亲和、弛豫和断裂机制，以及质子化、电子激发、微溶剂化和官能团取代的影响。光谱和量子化学结果的分析将在分子水平上详细了解这些基本物种的光物理和化学性质。此外，我们沿着质子化手性分子及其相互作用的新研究方向扩展了这些研究。手性和手性辨别在生命和材料科学的许多领域发挥着重要作用，其中许多现象在分子水平上还没有被理解。虽然在带电配合物中，相互作用和产生的手性辨别很强，但手性离子配合物的光谱信息很少。为此，我们将通过考虑(i) 1-氨基-2-吲哚醇（用于不对称合成）和（ii）谷氨酸（一种蛋白质原氨基酸和神经递质）的原型质子化（芳香）配合物来探索手性离子配合物中的相互作用。要解决的基本手性特定问题包括质子化对手性辨别强度的影响，单个力（斥力，静电，感应，色散）的重要性，以及极性和非极性溶剂化的影响，最终目标是提供分子水平上对带电手性配合物分子间相互作用和手性辨别的理解。

This project aims at the laser spectroscopic, mass spectrometric, and quantum chemical characterization of size-selected protonated aromatic molecules and their clusters isolated in the gas phase, to determine their geometric and electronic structure in the ground and excited electronic states. Target molecules are protonated (polycyclic) aromatic hydrocarbon molecules ranging from benzene to coronene, as well as simple derivatives and clusters with nonpolar and polar ligands (rare gas atoms, nitrogen, water) to mimic both hydrophobic and hydrophilic solvation. The considered molecules are of fundamental relevance in organic chemistry, combustion, biochemistry, and astrochemistry. Protonation has a huge impact on the electronic and geometric structure, because it reduces the symmetry and aromaticity of the aromatic pi-electron system and generates low-lying charge-transfer states. Hence, protonation largely changes the photochemistry and photophysics of these aromatic molecules, which are largely unexplored both experimentally and theoretically. In addition, the interaction with solvent molecules changes drastically upon protonation and electronic excitation, and a particular focus will be on proton transfer to/from solvent in microhydrated clusters. Fundamental questions to be addressed include the energy, structure, charge distribution, molecular orbitals, protonation site and proton affinity, relaxation and fragmentation mechanisms, as well as the effects of protonation, electronic excitation, microsolvation, and substitution of functional groups. The analysis of the spectroscopic and quantum chemical results will provide a detailed understanding of the photophysical and chemical properties of these fundamental species at the molecular level. In addition, we extend these studies along a new research line toward protonated chiral molecules and their interactions. Chirality and chiral discrimination play a fundamental role in a plethora of areas in life and materials sciences, and many of these phenomena are not understood at the molecular level. Although in charged complexes the interactions and resulting chiral discrimination are strong, little spectroscopic information is available for chiral ionic complexes. To this end, we will explore interactions in chiral ionic complexes by considering prototypical protonated (aromatic) complexes of (i) 1-amino-2-indanol (used in asymmetric synthesis) and (ii) glutamic acid (a proteinogenic amino acid and neurotransmitter). Fundamental chirality-specific questions to be addressed include the effects of protonation on the strength of chiral discrimination, the importance of the individual forces (repulsion, electrostatic, induction, dispersion), and the effects of polar and nonpolar solvation, with the ultimate goal of providing a molecular-level understanding of the intermolecular interactions and chiral discrimination in charged chiral complexes.