Exciplex-based multi-stimuli-responsive luminescent materials: photo-recoverable mechanochromic luminescence for reusable paper applications

Abstract

Stimuli-responsive luminescent materials can respond to external stimuli, exhibiting dynamic changes in their luminescent properties, and thus show broad application prospects in various fields such as optical sensing, security anti-counterfeiting, and information storage. The reversible recovery capability of luminescent response performance and the ease of implementation of recovery conditions are the core indicators for evaluating its practical application value. Herein, a complex (Cd2(9-AC)4(IM)2, 9-HAC for anthracene-9-carboxylic acid and IM for imidazole) system based on exciplex luminescence have been constructed. By disrupting the interactions between donor (9-HAC) and acceptor (IM) molecules through force-induced action or acid-induced action, mechanochromic luminescence (MCL) and acidochromic luminescence (ACL) properties are achieved. All these stimulus-induced luminescent changes can be reversibly restored through conventional solvent or alkali vapor fumigation. Notably, MCL performance can also be restored via ultraviolet irradiation, which is more cost-effective, convenient and environmentally friendly. This process is achieved through the repair of charge transfer pathways between donor and acceptor molecules by photogenerated free radicals. Leveraging the reversible MCL and photo-recoverable luminescence of this complex, we have ultimately designed a reusable paper capable of ink-free writing and solvent-free erasing, opening an entirely new path for promoting environmentally friendly and sustainable paper applications.