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Unusual Aggregation‐Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion
Author(s) -
Bu Fan,
Duan Ruihong,
Xie Yujun,
Yi Yuanping,
Peng Qian,
Hu Rongrong,
Qin Anjun,
Zhao Zujin,
Tang Ben Zhong
Publication year - 2015
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201506782
Subject(s) - intramolecular force , rigidity (electromagnetism) , aggregation induced emission , chemistry , propeller , quenching (fluorescence) , photochemistry , excited state , ring (chemistry) , coumarin , molecule , fluorescence , stereochemistry , materials science , atomic physics , organic chemistry , physics , optics , marine engineering , composite material , engineering
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.