Unusual Aggregation‐Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion |
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| Authors: | Fan Bu Ruihong Duan Yujun Xie Dr. Yuanping Yi Dr. Qian Peng Dr. Rongrong Hu Prof. Anjun Qin Prof. Zujin Zhao Prof. Ben Zhong Tang |
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| Affiliation: | 1. State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China);2. Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China);3. Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (China) |
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| 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. |
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| Keywords: | aggregation‐induced emission coumarins density functional calculations excited‐state decay intramolecular twisting |
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