Department of Chemistry, Indian Institute of Technology (Banaras Hindu University), Varanasi - 221005, U.P., India.
Phys Chem Chem Phys. 2018 Sep 19;20(36):23762-23772. doi: 10.1039/c8cp04579h.
A fluorescent metallogel (1% w/v) has been synthesized from non-fluorescent ingredients viz. the smallest possible low molecular weight aromatic symmetrical ligand H2SA (1) and LiOH in a chloroform and methanol mixture. The chelation of Li+ is not only responsible for the inhibition of excited state intramolecular proton transfer (ESIPT) or the origin of fluorescence through chelation enhanced fluorescence (CHEF) in 1, but also for aggregation leading to gelation. The metallogel obtained from 1/Li+ reveals a fibrous morphology while 1 with other, bigger size, alkali metal ions like Na+/K+/Cs+ demonstrates the growth of crystals with different shapes. The effect of the size of the alkali metal ion over gel formation is well explored by FTIR, UV-vis, fluorescence, average lifetime measurements, SEM and PXRD. The metallogel shows multi-stimuli responsive behaviour towards thermal and mechanical stress as well as reswelling properties. The regioisomer H2PBA (2) also shows emission upon treatment with LiOH due to the presence of intramolecular charge transfer (ICT), this is well established by various experiments. The mechanism of gel formation is well established by FTIR, 1H NMR, UV-vis, fluorescence, lifetime measurements, SEM and single crystal and powder XRD instrumental techniques. The involvement of various phenomena in gel formation has been further supported by other synthesized model compounds viz. H2MBA (3), PMO (4), H2SEA (5) and H2SPA (6). True gel phase material is proved by detailed rheological experiments.
已合成了一种荧光金属凝胶（1%w/v），其原料为非荧光成分，即尽可能小的低分子量芳香对称配体 H2SA（1）和 LiOH，在氯仿和甲醇混合物中。Li+的螯合不仅负责抑制激发态分子内质子转移（ESIPT）或通过螯合增强荧光（CHEF）在 1 中产生荧光的起源，而且还负责导致凝胶化的聚集。从 1/Li+获得的金属凝胶呈现纤维形态，而 1 与其他、更大尺寸的碱金属离子如 Na+/K+/Cs+则表现出不同形状的晶体生长。通过 FTIR、UV-vis、荧光、平均寿命测量、SEM 和 PXRD 充分探索了碱金属离子尺寸对凝胶形成的影响。金属凝胶对热和机械应力以及再溶胀性能表现出多刺激响应行为。由于存在分子内电荷转移（ICT），H2PBA（2）在与 LiOH 处理后也显示出发射，这通过各种实验得到了很好的确证。通过 FTIR、1H NMR、UV-vis、荧光、寿命测量、SEM 和单晶及粉末 XRD 仪器技术，很好地确定了凝胶形成的机制。通过其他合成模型化合物 H2MBA（3）、PMO（4）、H2SEA（5）和 H2SPA（6），进一步支持了凝胶形成中涉及的各种现象。通过详细的流变学实验证明了真正的凝胶相材料。
