Excited State Charge‐Transfer Complexes Enable Fluorescence Color Changes in a Supramolecular Cyclophane Mechanophore. (31st August 2022)

• Record Type: Journal Article
• Authors: Thazhathethil, Shakkeeb; Muramatsu, Tatsuya; Tamaoki, Nobuyuki; Weder, Christoph; Sagara, Yoshimitsu
• Is Part Of: Angewandte Chemie. Volume 134:Number 42(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-31
• Subjects: Charge Transfer -- Cyclophanes -- Elastomers -- Mechanochromic Luminescence -- Supramolecular Mechanophores; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202209225
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Mechanochromic mechanophores are reporter molecules that indicate mechanical events through changes of their photophysical properties. Supramolecular mechanophores in which the activation is based on the rearrangement of luminophores and/or quenchers without any covalent bond scission, remain less well investigated. Here, we report a cyclophane‐based supramolecular mechanophore that contains a 1, 6‐bis(phenylethynyl)pyrene luminophore and a pyromellitic diimide quencher. In solution, the blue monomer emission of the luminophore is largely quenched and a faint reddish‐orange emission originating from a charge‐transfer (CT) complex is observed. A polyurethane elastomer containing the mechanophore displays orange emission in the absence of force, which is dominated by the CT‐emission. Mechanical deformation causes a decrease of the CT‐emission and an increase of blue monomer emission, due to the spatial separation between the luminophore and quencher. The ratio of the two emission intensities correlates with the applied stress. Abstract : A new cyclophane‐based supramolecular mechanophore is developed. The mechanophore exhibits charge‐transfer complex emission in the force‐free state and exhibits monomer emission upon application of mechanical force due to spatial separation of the luminophore and quencher. Polyurethane elastomer films in which the mechanophore is covalently embedded exhibit instantly reversible emission color change. The emission change is correlated with the applied stress.