Synthesis And Properties Of Novel Photochromic Compounds Containing Bipyridyl Groups

Functional materials that can modulate the physical properties between two states by optical,electrical or chemical agents have potential application background in information storage,where diarylethene photochromic molecules have excellent fatigue resistance and characteristics,thermal stability,high cyclization quantum yield,fast response time and solid state reactivity,and can adjust fluorescence emission,ultraviolet absorption,electrochemical properties,optical rotation,magnetic properties,electron transfer,refractive index and dielectric constant by illumination.It is therefore recognized as having special application potential in ultra-high density optical data storage and light-controlled molecular switches.The design and synthesis of novel multifunctional diarylethylene molecule having excellent properties is the key to its application.A novel bipyridyl group-containing compound,3-bromo-2-methyl-5-（5’-bipyridyl）thiophene（BM-5-BPT）and photochromic molecule 1,2-double-[2’-Methyl-5’-（5"-bipyridyl）3’-thiophene]perfluorocyclopentene（BM-5-BP-3-TP or LO）was designed and synthesized.The closed-loop Lc formed by L_o conversion was obtained by column chromatography,and the structure of BM-5-BPT and the open-loop state LO and the open-loop state L_C of BM-5-BP-3-TP was characterized by infrared spectroscopy,nuclear magnetic resonance hydrogen spectroscopy,mass spectrometry and elemental analysis.The photochromic properties and solvent dependence of BM-5-BP-3-TP in the liquid phase were investigated by UV-Vis spectroscopy.The photochromic properties and fatigue resistance of PMMA film phase were also disscussed.Changes in wettability of the solid surface before and after the photochromic reaction were further studied.The main findings of this paper are as follows:（1）Elemental analysis,infrared spectroscopy,nuclear magnetic resonance hydrogen spectroscopy and mass spectrometry were used to prove that the structure of the synthesized product was consistent with the expected.（2）The molar absorption coefficients of the open-loop LO and the closed-loop L_C are calculated to be 4.1×10⁴ L·moL^-1·cm^-1 and 1.1×10⁴ L·moL^-1·cm^-1,respectively.The conversion rate of closed loop reaction is 73%.（3）UV-visible spectroscopy study shows that BM-5-BP-3-TP changes its color from colorless to blue after being exposed to ultraviolet light in methylene chloride and a new absorption peak appears at 607 nm in the visible region,whose location is consistent with that of the maximum absorption peak of the pure closed-loop Lc in the visible region of methylene chloride.It proves that the structure of BM-5-BP-3-TP is converted from hexatriene to cyclohexadiene,which completes the photoinduced cyclization reaction.（4）UV-Vis spectroscopy study shows that BM-5-BP-3-TP has reversible photochromic properties in the liquid phase and solid state,and the maximum absorption peak of the closed-loop state increases with the polarity of the solvent in different solvents.The maximum absorption wavelengths in n-hexane,dichloromethane,tetrahydrofuran and methanol were 596 nm,607 nm,608 nm and 612 nm,respectively,which showed a positive effect of solvent.（5）Molecular reaction kinetics study shows that the BM-5-BP-3-TP photocyclization reaction conforms to the zero-order reaction kinetics in a certain range when irradiated with constant intensity light,whose rate is independent of the molecular concentration,relatively speaking,the ring-opening reaction conforms to a first-order reaction kinetic process.（6）BM-5-BP-3-TP has reversible photochromic properties in the PMMA film phase,and the maximum absorption peak of whose closed-loop state in the visible region is 608 nm,and it has good fatigue resistance.After 20 reversible open-closed loop reaction cycle,there is no significant change in absorbance.（7）The photoinduced cyclization reaction causes changes in the structure and conjugation of the material,which leads to a change in surface wettability.As a result,after UV irradiation,the water contact angle was reduced from 81°±2 to 71°±2 for the surface of BM-5-BP-3-TP solid phase powder,and from 87°±2 to 80°±2 for the surface of PMMA film,respectively.