Kim Jinseok, Oh Juwon, Park Seongchul, Zafra Jose L, DeFrancisco Justin R, Casanova David, Lim Manho, Tovar John D, Casado Juan, Kim Dongho
Spectroscopy Laboratory for Functional π-electronic Systems and Department of Chemistry, Yonsei University, Seoul, 03722, Korea.
Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan, 46241, Korea.
Nat Commun. 2019 Nov 1;10(1):4983. doi: 10.1038/s41467-019-12986-w.
The scientific significance of excited-state aromaticity concerns with the elucidation of processes and properties in the excited states. Here, we focus on TMTQ, an oligomer composed of a central 1,6-methano[10]annulene and 5-dicyanomethyl-thiophene peripheries (acceptor-donor-acceptor system), and investigate a two-electron transfer process dominantly stabilized by an aromatization in the low-energy lying excited state. Our spectroscopic measurements quantitatively observe the shift of two π-electrons between donor and acceptors. It is revealed that this two-electron transfer process accompanies the excited-state aromatization, producing a Baird aromatic 8π core annulene in TMTQ. Biradical character on each terminal dicyanomethylene group of TMTQ allows a pseudo triplet-like configuration on the 8π core annulene with multiexcitonic nature, which stabilizes the energetically unfavorable two-charge separated state by the formation of Baird aromatic core annulene. This finding provides a comprehensive understanding of the role of excited-state aromaticity and insight to designing functional photoactive materials.
激发态芳香性的科学意义涉及对激发态过程和性质的阐释。在此，我们聚焦于TMTQ，一种由中心的1,6-亚甲基[10]轮烯和5-二氰基甲基噻吩外围基团组成的低聚物（受体-供体-受体体系），并研究在低能激发态中由芳构化主导稳定的双电子转移过程。我们的光谱测量定量地观测到了两个π电子在供体和受体之间的转移。结果表明，这种双电子转移过程伴随着激发态芳构化，在TMTQ中产生了一个贝德芳香性的8π核心轮烯。TMTQ每个末端二氰基亚甲基基团上的双自由基特性使得8π核心轮烯具有类似准三重态的构型以及多激子性质，通过形成贝德芳香性核心轮烯来稳定能量上不利的双电荷分离态。这一发现为全面理解激发态芳香性的作用以及设计功能性光活性材料提供了见解。
