Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 205A, 69120 Heidelberg, Germany.
Physikalisch-Chemisches Institut, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.
Phys Chem Chem Phys. 2023 Jul 5;25(26):17079-17091. doi: 10.1039/d3cp01916k.
N-Heteropolycycles (NHPCs) represent a promising substance class for applications in functional organic materials, since their electronic structure and the resulting individual molecular properties are efficiently tuneable by number and position of nitrogen atoms in the aromatic structural backbone. The isosteric replacement of a C-H unit by N leaves the geometric structure unchanged, while ionization potential, electron affinity and absorption spectra are altered. In this prespective, we present the potent combination of two-photon photoelectron spectroscopy (2PPE) and high-resolution electron energy loss spectroscopy (HREELS) with quantum chemical calculations for the investigation of the electronic structure of NHCPs. In contrast to conventional optical spectroscopies, 2PPE provides insight into electron-detached and attached electronic states of NHCPs, while HREELS delivers the energetic position of the lowest triplet states. Based on our comprehensive investigations, an extension of Platt's famous nomenclature of the low-lying excited ππ* states could be suggested for NHPCs based on the physical properties of the corresponding excitons. Also, the influence of N-introduction onto the occurrence of the so-called α-band in NHPCs compared to the parent polycyclic aromatic hydrocarbons could be explained in detail. While N-substitution of C-H in polycyclic aromatic hydrocarbons (PAHs) is often seen as a simple isosteric replacement, it has a strong influence on the electronic structure and the resulting properties. Therefore rules derived for PAHs can often only be transferred to a limited extent or not at all.
杂多氮环化合物（NHPCs）是一类很有前途的功能有机材料，因为它们的电子结构和由此产生的单个分子性质可以通过芳香结构骨架中氮原子的数量和位置来有效地调节。用氮原子取代 C-H 单元不会改变几何结构，而电离势、电子亲和能和吸收光谱会发生改变。在这个观点中，我们提出了双光子光电电子能谱（2PPE）和高分辨率电子能量损失谱（HREELS）与量子化学计算相结合，用于研究 NHPCs 的电子结构。与传统的光学光谱相比，2PPE 提供了对 NHPCs 中电子脱附和附加电子态的深入了解，而 HREELS 提供了最低三重态的能量位置。基于我们的综合研究，可以根据相应激子的物理性质，为 NHPCs 提出扩展 Platt 著名的低能激发ππ*态命名法。此外，与母体多环芳烃（PAHs）相比，NHPCs 中 N 引入对所谓α带的出现的影响可以详细解释。虽然在多环芳烃（PAHs）中 C-H 的 N 取代通常被视为简单的等排取代，但它对电子结构和由此产生的性质有很大影响。因此，为 PAHs 推导的规则通常只能在有限的程度上或根本不能转移。
