Design, Synthesis And Research Of Photochromism Molecular Switches

Information technology has revolutionized daily life in the last decades andthe continuously increasing amount of data to be stored and manipulated stronglystimulated the search for switching and memory elements as tiny as a singlemolecule. Molecular switches can be converted from one state to another by anexternal stimulus such as light, electricity or a chemical reaction. Like with theirmacroscopic counterparts, one is able to control numerous functions and propertiesof materials and devices.Some of the optical molecular switches emerged from well-knownphotochromic dyes, others are based on entirely new design principles. In abroader context, the design of molecular switches present a formidable challengeon the road toward miniaturization in future nanotechnology.Azobenzene and many of its derivatives are characterized by reversibletransformations from the generally more stable trans form to the less stable cisform upon irradiation with UV or visible light to yield a photostationarycomposition that is wavelength and temperature dependent. Azobenzene is thus atextbook representative demonstrating the rotoresistant property of the N=Ndouble bond, and spectroscopists and photochemists have long been aware of theinversion-rotation mechanistic dichotomy. Many theoretical and experimentalpapers deal with this subject.In this thesis, we synthesized three kinds of molecular switches and a novelelectroactive azo polyamide and the properties of these compounds were studied.The thesis could be summarized as the points shown below:1. Synthesis of a "light-driven molecular butterfly": rigid macrocyclicoligomer with double azo moietiesA novel "light-driven molecular butterfly" was synthesized successfully andcharacterized with MS, IR and 1H NMR. When this compound was exposedwith different wavelength light, azobenzene moieties underwent trans/trans tocis/cis photoisomerization, resulting in the open-close motion just like abutterfly. Its three structural isomers were modelized by theoreticalcalculations and their thermal stabilities were also investigated. The potentialapplication of such light-induced mechanical motions at the molecular levelcould provide some insight into the workings of a molecular machine.2. Synthesis of a rigid macrocyclic oligomer with one azo group.A novel "light-driven" rigid macrocyclic oligomer with one azo group wassynthesized successfully and characterized with MS, IR and 1H NMR.Azobenzene moiety in the cyclic chain underwent trans/cis photoisomerizationwhen it was exposed with different wavelength light. The isomerization ofazobenzene group can change into the motion of the entire molecule andchange the shape of the central cavity. Characterization of the shape, size andproperties of nanometer-scale macrocyclic molecules obtained from variousamphiphiles is of great importance not only for the study of the structure andfunction of nanostructured membrane systems, but also for the potentialapplications, such as drug entrapment and release, and photochemical solarenergy conversion3. Synthesis and characterization of a Novel Azo Compound with"Dumbbell" SharpA novel azo compound with "dumbbell" shape was synthesized successfullyand characterized with MALDI-MS,FT-IR,elemental analysis,1H NMR and13C NMR. UV-Vis spectrum was used to monitor the trans-cis isomerization.The trans and cis isomers of the "dumbbell" shape azo compound are bothstable in room temperature because of the big end group. The molecularstructures were estimated by ab initio quantum chemical calculations. TheHF/6-31G* method was used, and the geometrics were fully optimized.4. Synthesis and Characterization of Electroactive azo Polyamide withAmine-Capped Aniline Pentamer in the Main ChainAn alternating copolymer, electroactive azo polyamide was prepared byoxidative coupling polymerization of oligoaniline macromonomer andp-phenylenediamine. The molecular structure of the copolymer wascharacterized with FTIR, 1H NMR spectroscopy, elemental analysis and gelpermeation chromatography (GPC). UV-Vis spectra was used to monitor thechemical oxidation process and cyclic voltammetry (CV) was used to checkthe electrochemical activity of the polyazoamide. In addition TGA was used toprobe the thermal characteristics of the copolymers. The photoisomerization ofthe polymer occurred with the irradiation of different wavelength light.