微小な力を検出・可視化するシクロファン型超分子メカノフォア

抄録

Mechanochromic mechanophores are molecular structures that visualize applied force. The mechanophores, covalently incorporated into a polymeric material, are activated in response to force through the polymer chain, allowing evaluation and visualization of mechanical damage to the polymeric materials. Most mechanophores have been reported to change absorption and/or photoluminescence properties upon force-induced cleavage of covalent bonds. In contrast, our group has developed supramolecular mechanophores that are activated without covalent bond scission, resulting in instant and reversible mechanochromic behavior. To date, we have developed two types of cyclophane-based supramolecular mechanophores. One is based on switching between excimer and monomer emission. The prototype has two 1,6-bis(phenylethynyl)pyrene groups as fluorophores. The cyclophane mechanophore incorporated into a segmented polyurethane elastomer exhibits excimer emission in the force-free state. When the film is deformed, the fluorophores are separated and the excimer emission intensity decreases. When the force is removed, the initial emission spectrum recovers. The mechanophore also works in hydrogels. The other type uses emission from charge transfer（CT）complexes between an electron-rich luminophore and an electron-deficient pyromellitic diimide（PMDI). The polyurethane elastomer films containing the mechanophores change their photoluminescence properties from CT emission dominant to monomer emission dominant. In addition, the length of the linker between the luminophore and PMDI is found to affect the mechanoresponsive luminescence.