Visible-light excitable thermally activated delayed fluorescence from hydrogen-bonded D-A aromatic N-heterocycle/polymer material and the application for anti-counterfeiting

Thermally activated delayed fluorescence (TADF) polymer materials have shown promising potential in the optical information encryption. However, these materials still face challenges related to complex and toxic fabrication processes for guest molecules, transitional metal doping, expensive catalysts, toxic organic solvents, and the requirement of UV light excitation. To address these challenges, we present the facile synthesis of a crystalline intramolecular hydrogen-bonded D-A aromatic N-heterocycle crystal (DI-1) with suitable energy splitting between singlet and triplet excited states (ΔEST), which is achieved using a slow solvent diffusion method with ethanol as the resolvent. Furthermore, we propose a green and straightforward host-guest doping strategy by coupling DI-1 with water-soluble PVA (DI-1/PVA-0.3 wt%) through a water-promoted dispersion method. The DI-1/PVA-0.3 wt% composite exhibits high quantum efficiency and long TADF lifetime when excited by visible light at room temperature. These desirable properties are attributed to the appropriate ΔEST of DI-1 with D-A structure and the establishment of a hydrogen bonding network between DI-1 and PVA. Additionally, we demonstrate the facile fabrication of an anti-counterfeiting 2D code pattern using environmentally friendly and cost-effective screen printing techniques with DI-1/PVA-0.3 wt%. This pattern can be easily deciphered using white light, offering insights into commercial production for dual optical and digital security protection. Our work provides a strategy for the development of TADF materials that can be excited by visible light, showcasing their potential application in information encryption and decryption.