In situ generated dimethylamine constructs a robust hydrogen-bonded organic framework for selective fluorescence detection

Hydrogen-bonded organic frameworks (HOFs) are frameworks formed by organic building blocks through hydrogen bonding forces with promising applications in various fields. However, their development has been hindered by poor stability. In this work, a multiple hydrogen bond strategy with in situ generation of dimethylamine (DMA) is proposed to design robust HOFs. The protic acid HCl and Lewis acid Ag+ catalyze the cleavage of the amide C-N bond in the solvent N,N-dimethylformamide (DMF) molecules to generate dimethylamine (DMA) molecules in situ. Then, DMA molecules form multiple hydrogen bonds with dicarboxylic phenylporphyrin (DBP), and build a crystalline hydrogen-bonded organic framework (DBP-HOF), utilizing both their donor and acceptor on the N atom of each DMA molecule. Additionally, DBP's large pi conjugate structure contributes to stabilizing DBP-HOF through strong pi-pi stacking interactions. Notably, DBP-HOF demonstrates excellent fluorescence performance for selective detection of Cu2+, as well as responsiveness towards methylene blue (MB) and indigo carmine (IC). Interestingly, each analyte elicits distinct fluorescence behavior from DBP-HOF, enabling their effective differentiation. This study holds significant implications for designing stable HOF materials and advancing their application in optical sensing.