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Turn‐On Fluorescence in Tetra‐NHC Ligands by Rigidification through Metal Complexation: An Alternative to Aggregation‐Induced Emission
Author(s) -
Sinha Narayan,
Stegemann Linda,
Tan Tristan T. Y.,
Doltsinis Nikos L.,
Strassert Cristian A.,
Hahn F. Ekkehardt
Publication year - 2017
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.201610971
Subject(s) - tetraphenylethylene , chemistry , fluorescence , tetra , intersystem crossing , intramolecular force , photochemistry , phosphorescence , moiety , aggregation induced emission , metal , turn (biochemistry) , singlet state , excited state , stereochemistry , medicinal chemistry , organic chemistry , physics , quantum mechanics , nuclear physics , biochemistry
Abstract Two tetraphenylethylene (TPE) bridged tetraimidazolium salts, [H 4 L ‐Et](PF 6 ) 4 and [H 4 L ‐Bu](PF 6 ) 4 , were used as precursors for the synthesis of the dinuclear Ag I and Au I tetracarbene complexes [Ag 2 ( L ‐Et)](PF 6 ) 2 , [Ag 2 ( L ‐Bu)](PF 6 ) 2 , [Au 2 ( L ‐Et)](PF 6 ) 2 , and [Au 2 ( L ‐Bu)](PF 6 ) 2 . The tetraimidazolium salts show almost no fluorescence ( Φ F <1 %) in dilute solution while their NHC complexes display fluorescence “turn‐on” ( Φ F up to 47 %). This can be ascribed to rigidification mediated by the restriction of intramolecular rotation within the TPE moiety upon complexation. DFT calculations confirm that the metals are not involved in the lowest excited singlet and triplet states, thus explaining the lack of phosphorescence and fast intersystem crossing as a result of heavy atom effects. The rigidification upon complexation for fluorescence turn‐on constitutes an alternative to the known aggregation‐induced emission (AIE).