Höfener Sebastian, Günther Benjamin A R, Harding Michael E, Gade Lutz H
Institute of Physical Chemistry , Karlsruhe Institute of Technology (KIT) , P.O. Box 6980, D-76049 Karlsruhe , Germany.
Anorganisch-Chemisches Institut , Universität Heidelberg , Im Neuenheimer Feld 270 , 69120 Heidelberg , Germany.
J Phys Chem A. 2019 Apr 11;123(14):3160-3169. doi: 10.1021/acs.jpca.8b12296. Epub 2019 Mar 29.
The UV-vis absorption and emission spectra of halogenated tetraazaperopyrenes (TAPPs) have been investigated employing second-order approximate coupled cluster (CC2) and (time-dependent) density functional theory (DFT). We have found that the qualitative estimates of (vertical) absorption and excitation energies are possible within a single particle picture based on frontier orbitals, but the single particle picture is not sufficient to achieve quantitative accuracy. Going from the single-particle picture to the many-particle picture improves the agreement with experimental results, but still no satisfying correlation of theory and experiment is obtained. The comparison of CC2- and DFT-based methods reveals that deviations from the experimental results cannot be explained by deficiencies of the electronic-structure methods but rather stem from neglecting vibrational effects. An agreement of theoretical results and experimental spectra is found for adiabatic excitation energies, which are given as energy differences of vibronic states, which are directly accessible using both theoretical and experimental methods. The most pronounced vibronic influence is found for the Stokes shifts, which are significantly overestimated by computing the vertical electronic transitions only. Based on the vibronic contributions, the small Stokes shift of the TAPP compounds can be explained by the temperature dependence of the vibrationally resolved UV-vis spectra.
采用二阶近似耦合簇（CC2）和（含时）密度泛函理论（DFT）研究了卤代四氮杂苝（TAPPs）的紫外可见吸收光谱和发射光谱。我们发现，基于前沿轨道的单粒子图像可以对（垂直）吸收和激发能进行定性估计，但单粒子图像不足以实现定量精度。从单粒子图像过渡到多粒子图像提高了与实验结果的一致性，但仍然没有获得理论与实验之间令人满意的相关性。基于CC2和DFT方法的比较表明，与实验结果的偏差不能用电子结构方法的缺陷来解释，而更多地源于忽略了振动效应。绝热激发能的理论结果与实验光谱一致，绝热激发能以振动态的能量差给出，可通过理论和实验方法直接获得。在斯托克斯位移中发现了最显著的振动态影响，仅计算垂直电子跃迁会显著高估斯托克斯位移。基于振动态贡献，TAPP化合物的小斯托克斯位移可以通过振动分辨紫外可见光谱的温度依赖性来解释。
