Institut für Anorganische und Analytische Chemie and NRW Graduate School of Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149, Münster, Germany.
Physikalisches Institut and Center for Nanotechnology (CeNTech), Westfälische Wilhelms-Universität Münster, Heisenbergstrasse 11, 48149, Münster, Germany.
Angew Chem Int Ed Engl. 2017 Mar 1;56(10):2785-2789. doi: 10.1002/anie.201610971. Epub 2017 Jan 27.
Two tetraphenylethylene (TPE) bridged tetraimidazolium salts, H L-Et and H L-Bu , were used as precursors for the synthesis of the dinuclear Ag and Au tetracarbene complexes Ag (L-Et) , Ag (L-Bu) , Au (L-Et) , and Au (L-Bu) . The tetraimidazolium salts show almost no fluorescence (Φ <1 %) in dilute solution while their NHC complexes display fluorescence "turn-on" (Φ 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).
