Mechanical Force Induced Reversible Fluorescence Switching Of3-Aryl-2-Cyano Acrylamide Derivatives

Organic solid fluorescent materials have attracted much attention due to their excellent photoelectric properties, especially on the fields of organic optoelectronic devices、organic fluorescent sensors、anti-fake label. To tune and control the color of fluorescent materials is the key point of the researchers work now. Nowadays it can be achieved by changing the molecular chemical structures or the modes of solid state molecular packing. As changing the molecular chemical structures always needed chemical reactions, the insufficient reaction and mean reaction conditions restricted the development greatly. So more efforts were spent on the second way. Stimuli responsive fluorescent materials always have two or more than two kinds of color, which means they have different molecular stacking. It’s much easier for people to changing the molecular stacking by altering the weak molecular interaction, and the chemical structure won’t be destroyed which means the color can be switched reversibly many times without fatigue. Stimulate responsive materials included gasochromic materials、photochromic materials、 thermochromic material and piezochromic materials. Though piezochromic materials come to our sight in rescent years, much attention were paid because of its wide application prospect. As we don’t have an insight in the mechanism of the piezochromic phenomenon, these materials are still rare and the investigation of the influence between its structure and piezochromic ability is deeply needed. In this paper, a series of3-aryl-2-cyano acrylamide derivatives were synthesized and the relationship between structure and piezochromic behavior were investigated.In chapter2, two structural-simple3-aryl-2-cyano acrylamide derivatives (CDPA-E and CDPA-P) were synthesized and characterized by NMR, MS, IR and single crystal. It was found that both of them exhibited obvious piezofluorochromic properties. The as-prepared yellow-green compounds were both converted to orange-red after grinding with a spatula. All the ground samples can be recovered to its original color by heating at80℃over5mins or fuming with solvents like DCM, ethanol, ethyl acetate etc. The changes in fluorescence color can be attributed to the phase transition between crystalline (order) state and amorphous (disorder) state according to the Powder XRD spectrum. At the molecular level, the extension of the conjugation length and the formation of excimers are confirmed to account for the colors transition of CDPA-P and CDPA-E respectively. In addition, CDPA-P exhibited AIE activity which was caused by the restricted rotation of the molecules in the crystal state.In chapter3, the homolog CDPA-M was studied. It emitted orange-red but converted to bright-yellow when mixed with hydantoin. The complex was a piezochromic luminescent material while the CDPA-M was not. When ground by a spatula, the color of the complex was converted from bright-yellow to orange-red. And it can be recovered by heating or solvent fuming. As it’s revealed by XRD experiment, the different molecular stackings before and after grounding were responsible for the color change and the conversion between crystalline and amorphous state made the color change to be reversible.Finally, a series of3-aryl-2-cyano acrylamide derivatives with different length of alkoxy group were synthesized by Williamson ether reaction and Knoevenagel condensation. They all exhibited pizochromism properties. As the PL spectrum revealed, the PFC spectral shifts (APFC) decreased with the extension of alkyl length. The XRD spectrum demonstrated that the change of color can be attributed to the different molecular stacking.