Mechanochromic Luminescence of π-Conjugated Polymer Based on Pyridylenolate Boron Complexes: Molecular Design and Application to Shear-Force Memory
Yuto Aoyama, Shunichiro Ito, Kazuo Tanaka
Abstract
Mechanochromic luminescent (MCL) materials show emission color changes in response to external force. Although the development of MCL conjugated polymers is one of the hot topics because of their wide applicability for fabricating film-type mechanical and pressure sensors, it is still challenging to observe MCL behaviors from single-component polymer films. Herein, we report the MCL properties of the conjugated polymer consisting of boron pyridylenolate in film and its mechanism. We prepared copolymers involving pyridylenolate complexes bearing difluoride and diphenyl groups on boron and investigated their optical properties. Consequently, we found that the fluorine-substituted complex and especially its conjugated polymer showed clear MCL. From the mechanistic studies, we concluded that the degree of intermolecular interactions should play a key role in MCL behaviors. The boron complex units in the polymer main chain can detect microenvironmental changes in polymer morphology as luminescent color changes caused by the mechanical treatments owing to high environmental sensitivity. Finally, based on the sensitive MCL behaviors of the polymer, it was demonstrated that the polymer film was able to work as a shear-force memory at the tiny spot for needle puncture marks.