Reaction Time Induced a Two-Step Dissolution and Recrystallization Structural Transformation with Three Eu Metal–Organic Frameworks: Crystal Structures and Multiresponsive Fluorescence Detection
Huan Dai, Ya Zhang, Xiaoping Jin, Wensu Yang, Yunjie Luo, Ke Yang, Yu Fu, Wei Xu
Abstract
Under solvothermal conditions, three 3D lanthanide metal–organic frameworks (Ln-MOFs): [Eu(H 2 DHTA) 1.5 (DMF) 2 ]·DMF ( 1 ), [Eu(H 2 DHTA) 0.5 (DHTA) 0.5 (DMF)(H 2 O)]·2H 2 O ( 2 ), and Eu(HCOO) 3 ( 3 ) (H 4 DHTA = 2,5-dihydroxyterephthalic acid) have been synthesized by different reaction times. Interestingly, induced by reaction time, compounds 1–3 underwent a two-step dissolution and recrystallization structural transformation (DRST) reaction. Investigations on the DRST processes were carried out, and the transformation pathway was deduced, which was verified by XRD analyses. Notably, compound 2 demonstrates pronounced luminescence as well as high stability in water and other organic solvents. The fluorescent detection of furan antibiotics can serve as turn-off effects, and glutamic acid (Glu), aspartic acid (Asp), and riboflavin (VB 2 ) can serve as the turn-on effect. To explain the enhancing and quenching mechanisms, XRD, UV–visible absorption spectroscopy, electrochemistry, IR spectra, theoretical calculation, fluorescence lifetimes, and XPS were discussed. Additionally, MOF-coated test strips were utilized to detect these analytes, exhibiting excellent agreement with fluorescence spectroscopy. This work provides an example for more effective designs to employ Ln-MOFs as multiresponsive fluorescent sensors for detection of environmental pollutants in aqueous solution.