Multistimuli-Responsive Chromic Behaviors and Proton Conductivity within a Viologen-Based Hydrogen-Bonded Organic Framework

Abstract Hydrogen-bonded organic frameworks (HOFs) integrating stimuli-responsive properties and proton transport are promising functional materials; however, systems that combine reversible chromism with proton conduction remain rare. Herein, we report a viologen-based HOF (HOF-1) assembled from 1,1′-dibenzyl-4,4′-bipyridinium cations and 2,7-naphthalenedisulfonate anions via cooperative π–π stacking and hydrogen-bonding interactions. Single-crystal analysis reveals an ordered donor–acceptor arrangement with continuous hydrogen-bonded channels. HOF-1 exhibits good stability toward water, acidic/basic media, and thermal treatment, together with multistimuli-responsive chromic behaviors, including reversible photochromism, thermochromism, and ammonia-induced vapochromism. Its rapid light-yellow-to-green photochromic transition enables potential applications in QR-code anticounterfeiting. The chromic mechanism is supported by ESR, XPS, and DFT analyses. In addition, HOF-1 shows a proton conductivity of 1.07 × 10–3 S cm–1 at 80 °C and 98% RH, with an activation energy of 0.40 eV, attributed to the continuous hydrogen-bonded transport pathways. This work provides a viable strategy for developing multifunctional HOFs that integrate chromic response with proton conduction for sensing, information security, and ion-transport applications.