Spiral Intramolecular Charge Transfer and Large First Hyperpolarizability in Möbius Cyclacenes: New Insight into the Localized π Electrons

• Published in: Chemphyschem Vol. 13; no. 9; pp. 2349 - 2353
• Main Authors: Zhong, Rong-Lin, Xu, Hong-Liang, Su, Zhong-Min, Li, Zhi-Ru, Sun, Shi-Ling, Qiu, Yong-Qing
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 18.06.2012; WILEY‐VCH Verlag; Wiley
• Subjects: Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); density functional calculations; Density-functional theory; Electric and magnetic moments (and derivatives), polarizability and magnetic susceptibility; electron transfer; electronic structure; Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Moebius compounds; Molecular properties and interactions with photons; Nonlinear optics; Optical susceptibility, hyperpolarizability; Optics; Physics; Properties of molecules and molecular ions; density functional calculations; Electronic structure; Unsaturated cyclic compound; electron transfer; Electric hyperpolarizability; Theoretical study; Density functional method; Moebius compounds; Möbius strip; Nonlinear optics; Pi electron system; Intramolecular charge transfer
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.201200213

Much effort has been devoted to investigating the unusual properties of the π electrons in Möbius cyclacenes, which are localized in a special region. However, the localized π electrons are a disadvantage for applications in optoelectronics, because intramolecular charge transfer is limited. This raises the question of how the intramolecular charge transfer of a Möbius cyclacene with clearly localized π electrons can be enhanced. To this end, [8]Möbius cyclacene ([8]MC) is used as a conjugated bridge in a donor–π‐conjugated bridge–acceptor (D–π–A) system, and NH2‐6‐[8]MC‐10‐NO2 exhibits a fascinating spiral charge‐transfer transition character that results in a significant difference in dipole moments Δμ between the ground state and the crucial excited state. The Δμ value of 6.832 D for NH2‐6‐[8]MC‐10‐NO2 is clearly larger than that of 0.209 D for [8]MC. Correspondingly, the first hyperpolarizability of NH2‐6‐[8]MC‐10‐NO2 of 12 467 a.u. is dramatically larger than that of 261 a.u. for [8]MC. Thus, constructing a D–π–A framework is an effective strategy to induce greater spiral intramolecular charge transfer in MC although the π electrons are localized in a special region. This new insight into the properties of π electrons in Möbius cyclacenes may provide valuable information for their applications in optoelectronics. Spiral π bridge: [8]Möbius cyclacene is used as a one‐sided π‐conjugated bridge in a donor–π–acceptor framework to induce large intramolecular electron transfer. For example, NH2‐6‐[8]MC‐10‐NO2 (see picture) shows dramatic enhancement of the first hyperpolarizability β0, because the difference in dipole moments Δμ between the ground and the crucial excited states is significantly increased.