title: Unusual Aggregation-Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion.
abstract: Aggregation-induced emission (AIE) is commonly observed for propeller-like luminogens with aromatic rotors and stators. Herein, we report that a coumarin derivative containing a seven-membered aliphatic ring (CD-7) but no rotors showed typical AIE characteristics, whereas its analogue with a five-membered aliphatic ring (CD-5) exhibited an opposite aggregation-caused quenching (ACQ) effect. Experimental and theoretical results revealed that a large aliphatic ring in CD-7 weakens structural rigidity and promotes out-of-plane twisting of the molecular backbone to drastically accelerate nonradiative excited-state decay, thus resulting in poor emission in solution. The restriction of twisting motion in aggregates blocks the nonradiative decay channels and enables CD-7 to fluoresce strongly. The results also show that AIE is a general phenomenon and not peculiar to propeller-like molecules. The AIE and ACQ effects can be switched readily by the modulation of molecular rigidity.
authors.affiliation: State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China).
authors.forename: Fan
authors.initials: F
authors.lastname: Bu
authors.affiliation: Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China).
authors.forename: Ruihong
authors.initials: R
authors.lastname: Duan
authors.affiliation: Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China).
authors.forename: Yujun
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China).
authors.forename: Yuanping
authors.initials: Y
authors.lastname: Yi
authors.affiliation: Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China). qpeng@iccas.ac.cn.
authors.forename: Qian
authors.initials: Q
authors.lastname: Peng
authors.affiliation: State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China).
authors.forename: Rongrong
authors.initials: R
authors.lastname: Hu
authors.affiliation: State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China).
authors.forename: Anjun
authors.initials: A
authors.lastname: Qin
authors.affiliation: State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China). mszjzhao@scut.edu.cn.
authors.forename: Zujin
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China). tangbenz@ust.hk.|Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (China). tangbenz@ust.hk.
authors.forename: Ben Zhong
authors.initials: BZ
authors.lastname: Tang
keywords: aggregation-induced emission; coumarins; density functional calculations; excited-state decay; intramolecular twisting