Kochman Michał Andrzej, Durbeej Bo
Division of Theoretical Chemistry, Department of Physics, Chemistry and Biology (IFM) , Linköping University , 581 83 Linköping , Sweden.
J Phys Chem A. 2019 Aug 8;123(31):6660-6673. doi: 10.1021/acs.jpca.9b02962. Epub 2019 Jul 25.
Donor-acceptor systems based on fulvene as the electron-accepting moiety are typified by exotic, strongly polar electronic structures. In this contribution, ab initio calculations have been performed to explore the ground- and excited-state properties of an archetypal compound of this class, which incorporates the exocyclic carbon atom of fulvene into a tetramethylimidazoline-like five-membered ring. In the electronic ground state, the compound under study has a pronounced zwitterionic character and is best described as consisting of a negatively charged cyclopentadienyl ring linked covalently to a positively charged tetramethylimidazolium ring. Both of these rings can be considered as aromatic. The excess negative charge localized on the cyclopentadienyl ring is highly labile in the photochemical sense: the low-lying valence excited states exhibit varying degrees of reverse charge transfer, whereby electron density is transferred from the cyclopentadienyl ring back onto the tetramethylimidazolium ring. The topographies of the excited-state potential energy surfaces favor rapid and efficient internal conversion at an extended, fulvene-like S/S conical intersection seam. As a consequence, the excited-state lifetime of this compound is predicted to be on the order of 100 fs.
以富烯作为电子接受部分的给体-受体体系具有奇特的、强极性的电子结构。在本论文中，我们进行了从头算计算，以探索这类典型化合物的基态和激发态性质，该化合物将富烯的环外碳原子并入类似四甲基咪唑啉的五元环中。在电子基态下，所研究的化合物具有明显的两性离子特征，最好描述为由一个带负电荷的环戊二烯基环与一个带正电荷的四甲基咪唑鎓环共价连接而成。这两个环都可被视为芳香性的。在光化学意义上，定域在环戊二烯基环上的过量负电荷非常不稳定：低能量的价激发态表现出不同程度的反向电荷转移，即电子密度从环戊二烯基环转移回四甲基咪唑鎓环上。激发态势能面的形貌有利于在一个扩展的、类似富烯的S/S锥形交叉缝处进行快速有效的内转换。因此，预计该化合物的激发态寿命约为100飞秒。
