Self-Assembly of Lanthanide-Based Metallogel Nanoplates into Microcubic Blocks as Self-Calibrating Luminescent Methanol Sensors

Abstract

Because of the serious physiological toxicity of methanol, detection of methanol in ethanol medium is tremendously significant. Herein, excellent luminescent lanthanide-based supramolecular metallogels were prepared with the conventional low-molecular-weight-gelator 1,3,5-benzenetricarboxylic acid (BTC) and the lanthanide trivalent cations (Tb 3+ and Eu 3+ ), which exhibit distinctive characteristic photoluminescent emission of lanthanides. These metallogels were synthesized depending on the one-step method of a high-concentration reaction synergized with heat-assisted ultrasound. The mechanical characteristics of the supramolecular metallogels were investigated through a rheological study. The scanning electron microscopy study revealed the supramolecular interconnection structure of microcubic blocks formed through irregular self-assembly of nanoplates. The bi-metallogel (Eu/Tb-G) with an obvious brilliant yellow emission signal was favorably fabricated via utilizing the lanthanide co-doping strategy and manifests the characteristic emission bands of lanthanide trivalent ions (Eu 3+ and Tb 3+ ) simultaneously. The energy-transfer behavior between Tb 3+ and Eu 3+ was systematically studied. What is striking is that methanol facilitates the increase of Tb 3+ fluorescence intensity without affecting the characteristic emission of Eu 3+ , and this phenomenon induces a unique emission proportion between Tb 3+ and Eu 3+ ions. Inspired by this, a self-calibrated fluorescence sensor of methanol is acquired, which adopts the dynamic emission of Tb 3+ that can vary continuously and regularly as the target identification detection signal and utilizes the static emission of Eu 3+ as the internal reference system. The change of fluorescence lifetime and quantum yield confirmed that this obvious visual optical color signal varying phenomenon can be ascribed to the internal energy-transfer process conversion caused by the unique host−quest interaction between methanol and Eu/Tb-G. In addition, the prepared Eu/Tb-G paper-based sensor has good stimulation response and recyclability to methanol vapor. The above discussion can establish Eu/Tb-G as a ratiometric and colorimetric fluorescent sensor for the detection of methanol and its vapor.

Engineering of Metal–Organic Frameworks as Ratiometric Sensors

“…The metallogels showed a typical photoluminescent emission of lanthanides (Figure 42). 135 The optical properties of all the metallogels showed comparable excitation spectra with a maximum at 300 nm as a result of the π−π* transition of BTC. 136 Under UV light, the metallogels Tb-G, Eu-G, and Eu/Tb-G showed green, pink, and yellow luminescence, which designated the antenna behavior of BTC for the sensitization of both Tb 3+ and Eu 3+ ions, 137,138 and additionally the emission of Eu 3+ ions can be precisely sensitized by Tb 3+ ions in Eu/Tb-G. 139,140 Upon excitation at 492 nm, the emission spectrum of Eu/Tb-G illustrates the energy transfer among Tb 3+ and Eu 3+ ( 5 D 4 → 7 F 6 43b), whereas in EtOH, the color remained unchanged.…”

“…Synthetic procedure for Xerogel Ln-G (Eu-G, Tb-G, and Eu/Tb-G) with their color under UV lamp (302 nm). Reproduced with permission from ref . American Chemical Society, Copyright 2021.…”

“…(Inset: Color of Eu/Tb-G xerogel in MeOH (right) and EtOH (left) under UV light). Reproduced with permission from ref . American Chemical Society, Copyright 2021.…”

“…Emission spectra of strip paper of Eu/Tb-G upon exposure of methanol vapor (green, inset: strip paper) and without methanol vapor (orange, inset: strip paper). Reproduced with permission from ref . American Chemical Society, Copyright 2021.…”

Switchable Supramolecular Configurations of Al3+/LysTPY Coordination Polymers in a Hydrogel Network Controlled by Ultrasound and Heat

“…Controlling the coordination-driven self-assembly of ligands in aqueous media, especially in hydrogels, provides a good platform to investigate intelligent materials in the fields of drug delivery, microsensors, catalysis, pharmaceutical crystal growth, tissue engineering, and biomaterials. − Especially, the coordination interaction changes of metallogels including association and dissociation, metal valence, and metal cores controlled by stimuli feature an array of exciting, reversible optical and electrochemical properties. − The resulting structural changes serve as a highly efficient approach to generate different kinds of self-assembled architectures and phases with multiple functions. For example, Yang has acquired a multiphase transition of Pt-based gels controlled by temperature-induced aggregation changes; Ishiwata has reported the transformation of hard MOF crystals to soft polymer gels, leading to chimera-type hybrid materials; and Zhang and Wei have demonstrated a coordination competition control in metallogels that is utilized for multiple analyte sensing. , These gels could be applied in many fields such as sensing platforms, simulation of biofunctions, information safety, and memory devices.…”