A 2D layered fluorescent crystalline porous organic salt†

Abstract

Crystalline porous organic salts (CPOSs), an emerging category of crystalline porous organic materials with potential applications in various fields, have garnered significant attention in recent years. However, the limited variety of building blocks, the non-directionality of ionic bonds, and the scarcity of design principles severely restrict the synthesis and widespread application of CPOSs, especially for two-dimensional (2D) CPOSs. Adopting suitable 2D building blocks is an effective way to construct 2D CPOSs with specific functions. Herein, a new CPOS (CPOS-9) with fluorescent properties has been synthesized by employing a four-node 2D fluorescent organic base and a linear two-node organic acid. Notably, CPOS-9 features a unique 2D layered structure formed by the aggregation of hydrophobic and hydrophilic groups, which stacks through electrostatic interactions rather than the conventional π–π stacking. With significant fluorescent characteristics and abundant binding sites within nanoconfined channels, CPOS-9 showcases high sensitivity and selectivity for Ce³⁺ detection, with a detection limit as low as 80 nM. Based on theoretical calculations, for the first time, an energy level matching mechanism is proposed to elucidate the fluorescence quenching observed during the detection of Ce³⁺ in porous organic materials. This work enriches the variety of 2D CPOSs and highlights their application in the detection of rare earth elements.