Unravelling the role of various interactions in mechanochromism induced polymorphism: acid fumes sensor kit and double encryption decryption technologies

Abstract

Majority of previously reported mechanochromic materials display crystalline to amorphous transition, thereby, inhibiting the detailed investigation of their mechanistic insight. Additionally, developing a multi-stimuli responsive system is critical in sensor and security technologies. In this context, a pyrene-based derivative (E)-N'-(anthracen-9-ylmethylene)furan-2-carbohydrazide (PCFH) displays aggregation induced emission (AIE), mechanochromism and acidochromism. It exhibits a relatively rare occurring reversible red-shifted enhanced emission upon mechanical force. The mechanochromism induced crystal to crystal transition is reported and the structural changes at molecular level is investigated with the aid of PXRD, SCXRD, DSC and Hirshfeld surface analysis. This study is among the rare reports that present single crystals of both polymorphs in pyrene-based materials. The mechanically-induced enhancement of molecular planarity facilitates ICT processes and alters the supramolecular arrangement from robust π–π stacking to C–H···π interactions leading to red-shifted enhanced emission. The acid sensitive property of PCFH has been successfully utilized in devising portable sensor kit for acidic fumes. Additionally, the acidochromism and mechanochromism has been synergistically exploited to design a multi-level data encryption decryption system. Furthermore, PCFH-coated papers enable the practical utility in pressure sensing and rewritable pressure printing technologies.