||Mechanoresponsive luminescence and liquid-crystalline behaviour of a cyclophane featuring two 1,6-bis(phenylethynyl)pyrene groups
Sagara, YoshimitsuTamaoki, Nobuyuki
47062 , 2017-11-17 , Royal Society of Chemistry
Cyclophanes have been attractive targets over recent decades because of their fascinating molecular structures and inherent ability to act as supramolecular hosts. However, cyclophanes that exhibit stimuli-responsive luminescence in their condensed states are still very rare, although luminescent cyclophanes could be suitable platforms for sophisticated photofunctional molecular assembled materials. We here report that a pyrenophane featuring two p-extended pyrene groups exhibits mechanoresponsive luminescence in the solid states and shows a nematic liquid-crystalline phase at elevated temperature. Two 1,6-bis(phenylethynyl)pyrene moieties form intramolecular excimers in a diluted chloroform solution, whereas no clear intra-and/or intermolecular excimer formation was observed for the solid state accessed through slow cooling from the nematic phase. Photoluminescence spectroscopic measurements, emission lifetime measurements, and X-ray diffraction patterns confirmed that mechanical stimuli result in conversion to much less ordered molecular assembled states in which some luminophores form excimers, leading to changes in photoluminescence colours.