Study On Fluorescent And Phosphorescent Materials Based On Aromatic Ketone-lewis Acid Complexes

Fluorescent and phosphorescent materials have great potentials in many fields such as chemical sensing, photoelectronic displaying and bioimaging. Thus developing novel fluorescent and phosphorescent materials remains hot in the whole science community. The Nobel Prize in Chemistry 2014 was awarded jointly to Eric Betzig, Stefan W. Hell and William E. Moerner "for the development of super-resolved fluorescence microscopy", indicating the cruitial importance of the novel fluorescence detection methods. I am honored to conduct reseach in the field of fluorescence and I have developed a series of fluorescent and phosphorescent materials based on aromatic-Lewis acid complexes as follows.1. We investigated the hydrochromic fluorescence of organo-boronium-avobenzone complexes. Commercially available avobenzone readily reacts with boron trichloride or tribromide to afford boron-bisavobenzone salts. The complexes were found to exhibit unusual solvent-dependent fluorescence in solution and hydrochromic fluorescence in the solid state:a blue-to-orange emission colour change was observed upon water vapour exposure. The phenomenon was likely caused by interference of the boron coordination sphere by water molecules.2. We investigated the sensitization of europium(Ⅲ) luminescence in water with β-diketone-poly(ethylene glycol) macroligand. Poly(ethylene glycol)-modified β-diketone macroligand is developed to sensitize europium(Ⅲ) ions in water. High luminescence intensity characteristic of Eu3+was achieved due to spontaneous formation of micelle-like structure in which the hydrophobic core prevents luminescence-quenching by water molecules. The pH is found to induce a quantitative ratio change in two fluorescence bands from both ligand and Eu3+.3. Primary alcohol-functionalized β-diketones (bdks) are successfully synthesized via facile one-step Claisen condensation between aromatic monoketones and ε-caprolactone (ε-CL). To demonstrate application potentials, these bdk alcohols are used to chelate with various Lewis acids, including Tb (Ⅲ), Eu (Ⅲ), and B (Ⅲ). It is discovered that the resulting Tb (Ⅲ) and Eu(Ⅲ) diketonate complexes can serve as both catalysts and initiators for ring-opening polymerization (ROP) under solvent-free conditions, using lactide monomer as an example. The polylactides (PLAs) thus obtained exhibit luminescence properties characteristic of Tb (Ⅲ) and Eu (Ⅲ), respectively. On the other hand, boron-chelated diketone can initiate ROP of lactide in the presence of Sn(oct)2, and affords a PLA material with dual-emission, i.e., fluorescence and room temperature phosphorescence. The synthesis described here represents a shortcut for the preparation of bdk-based macroligands and subsequent functional materials.4. Materials with both fluorescence and roomtemperature phosphorescence (RTP) can be useful in the field of optoelectronics. Here we present a general strategy, taking advantage of carbonyl compounds, which have been known to possess efficient intersystem crossing with high triplet state yield, as well as a strongly fluorescent intramolecular chargetransfer (ICT) state, to produce materials with both fluorescence and RTP at the same time, or dual-emission. In the presented model systems, in order to generate a suitable ICT state, Lewis acid binding to aromatic ketone derivatives has been proved to be a viable method. We have selected AICl3, BCl3, BF3, and GdCl3 as binding Lewis acids, in that they exhibit sufficiently strong binding affinity toward thearomatic ketone derivatives to afford stable complexes and yet do not possess low-lying electronic transitions vs the ligands. We have successfully observed dual-emission from these designed complexes in polymers, which act to suppress competitive thermal decay at room temperature. One of the complexes is particularly interesting as it is dual-emissive in the crystalline state. Single-crystal XRD reveals that the molecule forms multiple hydrogen bonds with its neighbors in crystals, which may significantly enhance the rigidity of the environment.