Temperature and Solvent Dual Switch Photochromic Chiral Ionic Hydrogen Bonded Organic Framework for Circularly Polarized Luminescence and Advanced Encryption

Abstract

Multi-response encryption materials with temperature control and time resolution have attracted widespread attention due to their unique response characteristics and higher application security. The design and development of photochromic crystalline materials with multiple stimulus responses remain challenging. In this study, we report a pair of responsive photochromic chiral ionic hydrogen bonded organic framework (iHOF) R/S-iHOF-19 controlled by both temperature and solvent through charge-assisted synthesis. The chromophore tetrakis(4-sulfophenyl)ethylene (H4TPE) acts as an electron donor and (1R/S,2R/S)-1,2-diphenylethylenediamine (R/S-DPEN) as an electron acceptor and chiral source. Water and methanol molecules connect the donor and acceptor and interact to build a 3D supramolecular framework. Notably, water and methanol molecules form independent hydrogen-bonding channels within the iHOF structural framework providing a transfer path for the photoinduced electrons. Surprisingly, the formation of a continuous chiral supramolecular framework by R/S-DPEN while generating photo-induced radicals under ultraviolet (UV) irradiation at -20 °C imparts excellent circularly polarised luminescence (CPL) properties to R/S-iHOF-19. The glum values reach -1.8 × 10-3 and +3.75 × 10-3, respectively, and show an enhancement of the circular polarisation of light with decreasing temperature. This CPL with unique low-temperature stimulus-responsive photochromism provides new guidance and perspectives for the development of information security and multiple encryption materials.