Clark Aurora E, Qin Changyong, Li Alexander D Q
Department of Chemistry, Washington State University, Pullman, Washington 99164, USA.
J Am Chem Soc. 2007 Jun 20;129(24):7586-95. doi: 10.1021/ja0687724. Epub 2007 May 23.
The diimide perylene motif exhibits a dramatic intensity reversal between the 0 --> 0 and 0 --> 1 vibronic bands upon pi-pi stacking; this distinct spectral property has previously been used to measure folding dynamics in covalently bound oligomers and synthetic biological hybrid foldamers. It is also used as a tool to assess organization of the pi-stacking, indicating the presence of H- or J-aggregation. The zeroth-order exciton model, often used to describe the optical properties of chromophoric aggregates, is solely a transition dipole coupling scheme, which ignores the explicit electronic structure of the system as well as vibrational coupling to the electronic transition. We have therefore examined the optical properties of gas-phase perylene tetracarboxylic diimide (PTCDI) and its chromophoric dimer as a function of conformation to relate the excited-state distributions predicted by exciton theory with that of time-dependent density functional theory (TDDFT). Using ground- and excited-state geometries, the Franck-Condon (FC) factors for the lowest energy molecular nature electronic transition have been calculated and the origin of the intensity reversal of 0 --> 0 and 0 --> 1 vibronic bands has been proposed.
二亚胺苝基序在π-π堆积时，0→0和0→1振动带之间呈现出显著的强度反转；这种独特的光谱性质此前已被用于测量共价结合的低聚物和合成生物杂交折叠体中的折叠动力学。它还被用作评估π-堆积组织的工具，表明存在H-或J-聚集。零阶激子模型常用于描述发色团聚集体的光学性质，它仅仅是一种跃迁偶极耦合方案，忽略了系统的明确电子结构以及与电子跃迁的振动耦合。因此，我们研究了气相苝四羧酸二亚胺（PTCDI）及其发色二聚体的光学性质随构象的变化，以将激子理论预测的激发态分布与含时密度泛函理论（TDDFT）的激发态分布联系起来。利用基态和激发态几何结构，计算了最低能量分子自然电子跃迁的弗兰克-康登（FC）因子，并提出了0→0和0→1振动带强度反转的起源。
