Nonaromatic Persistent Room-Temperature Phosphorescent Hydrogels with Shape Memory Behavior and Ultrahigh Elastic Moduli Based on Partially Hydrolyzed Polyacrylonitrile

Abstract

Organic room-temperature phosphorescent (RTP) hydrogels, especially those based on nontraditional luminogens, hold great potential for various applications. However, developing nonaromatic hydrogels with excellent mechanical properties and multifunctionality alongside long lifetimes remains challenging. Herein, a series of nonaromatic hydrogels with RTP are prepared by utilizing the hydrophobic interactions and coordinate bonding based on partially hydrolyzed polyacrylonitrile (PHPAN). The initial hydrogel exhibits strong fluorescence yet weak and short-lifetime RTP. When the hydrogel is treated by immersing in Zn²⁺ solution and a heating–cooling process, the obtained hydrogel exhibits significant RTP with a lifetime of 178.5 ms, excellent mechanical properties with an elastic modulus of 161.6 MPa, and a tensile strength of 10.9 MPa, as well as thermally stimulated shape memory behavior and anti-swelling property. The weak RTP emission of the initial hydrogel originates from the hydrophobic aggregation of cyano groups, and the dramatically improved RTP and mechanical properties arise from the formation and optimizing of Zn²⁺-carboxylate coordinate bonds during the immersing and heating–cooling processes and the enhanced hydrophobic interactions of cyano groups, which stiffens the hydrogel network and suppresses nonradiative decay. This work provides a reliable strategy for the development of mechanically strong multifunctional nonaromatic RTP hydrogels.