Cyclophanes comprise aromatic groups and aliphatic linkers bridging the aromatic moieties. Photoluminescent
cyclophanes have been mainly investigated in solution because formation of inclusion complexes with guest ions or
molecules changes the photophysical properties. In contrast, stimuli-responsive luminescent properties of luminescent
cyclophane in the crystalline or liquid-crystalline states have not been explored well, though cyclophanes would be
promising candidates of thermo- and/or mechanoresponsive luminescent materials. In this contribution, recent research
progress concerning luminescent cyclophanes prepared in my group is introduced. A 1,6-bis(phenylethynyl)pyrene-based
cyclophane featuring hexaethyleneglycol linkers shows a nematic liquid-crystalline phase showing blue-green emission
due to the excimer formation. Rapid cooling from the nematic phase leads to appearance of a supercooled nematic phase
and both the blue-green emission and the nematic molecular order are well retained. Subsequent annealing procedure
induces a phase transition to a crystalline phase showing blue emission. A 9,10-bis(phenylethynyl)anthracene-based
cyclophane having tetraetylene glycol linkers have been found to form two different quasipolymorphs. One crystalline
state exhibits two-step mechanochromic luminescence. Another crystal contains chloroform as the guest molecules and
mechanical or thermal stimuli induces release of the guest molecules. Differential scanning calorimetry and
thermogravimetric analysis clarified the phase transition behavior of the luminescent cyclophanes.
Keywords:cyclophane, fluorescence, liquid crystal, stimuli-responsive luminescence, excimer
Publication Date: 2022-10-25