Study Of "2+2" Cycloaddition In Biphenyl-Based Center Swivel-Cruciform Oligo(Phenylenevinylene)s

Synthesis chemistry is the basis of material preparing science, and is the central issue of chemical science. New organic chemistry reactions and new methods play a key role in promoting the development of chemical science and progress of material science. Under light or heat, the two vinyl units or conjugated double bonds interact with each other, which can undergo a [2+2] cycloaddition to form a stable four-ring structure. Four-ring structure is an important part of a lot of functional materials and new drugs, and [2+2] cycloaddition is a very effective way to build a four-ring structure, so the experimental and theoretical research on [2+2] cycloaddition is very meaningful.The theory of energy relevance is used to correlate the symmetry of molecular orbitals in different energy levels of reactants and products to illustrate the stereochemistry selection rules in cycloaddition reaction. In 1930s, Atomic relevance diagram was put forward, and two limiting cases of "split atoms" and "joint atoms" expressed qualitatively the nature of the molecular orbital with the changes of distance between the nuclei. With the atomic relevance diagram, Scientists can get the information about molecular level structure in the transition zone according to the energy level structures of split atoms and joint atoms. In 1960s, Woodward-Hoffman promoted the established atomic relevance diagram and draw energy level relevance diagram of cycloaddition, and successfully applied energy level relevance diagram to describe the stereochemical selection principles in these reactions, and this is the theory of energy level relevance .[2+2] cycloadditions can be divided into the light-induced and thermal-induced. According to some selection rules of the cycloaddition reaction, we can understand initially when theπelectrons arrange in supra-supra form, the reaction is heat-permited and light-forbidden for 4n+2πelectrons, at the same time, the reaction is heat-forbidden and light-permited for 4nπelectrons. However, when theπelectrons arrange in supra-antara form, the situation is completely reversed. In the excited state permited light-induced cycloaddition reactions, the twoπelectrons usually arrange parallelly, and the distance between theπelectrons is less than 4 ?. There are many ways to let the twoπelectrons arrange in parallel form, such as the way of supramolecular chemistry: crown ether-metal ion interaction, hydrogen bonds interaction, metal ion complex interaction, et al, and the interaction can limit the spatial location of double bonds. In the ground state permited thermal-induced cycloaddition reactions,πelectrons are not parallel, Woodward-Hoffman had predicted that when the twoπelectrons in orthogonal form, they would undergo a thermal [2+2] cycloaddition reaction. However, these are few examples of such kind, because it does not only consider the dihedral angle between twoπelectrons, but also concern their distance. The dihedral anglea and distance can cause molecular torsion and results in the improvement of the molecular stress. In the accumulationπsystem or the high tension bicyclic triene system, this kind ofπarrangement is reasonable.Biphenyl-Based center swivel-cruciform oligo(phenylenevinylene)s are synthesized by author's group, and these compounds have excellent photoelectric properties. Such materials are based on biphenyl as the center, and band the two divinylbenzene together to form a cross-type molecular structure. Their derivative 7,8-di(4-N,N-diphenylaminophenyl)-2,3,4,5-di(4-N,N-diphenylamino)styrylbenzobic- yclo[4.1.1]octane (hereinafter referred to as DPA-TSB) in mild conditions (room temperature, no light) will generate 7,8-di(4-N,N-diph- enylaminophenyl)-2,3,4,5-di(4-N,N-diphenylamino)styrylbenzobicyclo[4.1.1]octane (hereinafter referred to asβ-DPA-TSB). This reaction has the following some characteristics: Firstly, mild experimental conditions, no high temperature or light, room temperature; Then, the yield up to 100%; Last, a high degree stereochemical specificity. And the dissertation will study the following aspects of these reactions.Firstly, these will be a in-depth investigation in the reaction kinetics and thermodynamics. In the work of development from a new phenomenon to a new valuable reaction to materials science, the recognition on the reaction mechanism and applicability is the key problem to be solved. Speed of a reaction fully reflects the reaction rate, and the reaction rate will also affect its usefulness. In the aspect of the reaction kinetics, according to the reaction characteristics, the author have used various methods such as NMR internal standard method, NMR external standard method, dual-wavelength spectrophotometry, and so on, to study the kinetics in different temperatures or different solvents. And the author did not only study the reaction characteristics of swivel-cruciform molecules, but also compare with non-swivel-cruciform molecules in order to further understand the supramolecular interaction catalytic cycloaddition.Further, According to the kinetics data, the author also studied the thermodynamics characteristics in details, such as reaction activation enthalpy, activation entropy and Gibbs free energy, in order to find out the possibility and degree of difficulty of the reaction.Finally, the author has further looked into the internal factors (biphenyl m-substituents, end substituents and biphenyl center) and external factors (temperature, light and solvent) from the experimental and theoretical aspects, and then put forward and proved the mechanism, so that these is a comprehensive scan on the reaction characteristics and a good base to the applicability of the reaction. Based on supramolecular interaction catalysis, the author has found and studied the [2+2] cycloaddition reaction in biphenyl-based center swivel-cruciform oligo(Phenylenevinylene)s. The author has researched the reaction kinetics, thermodynamics, effect factors and the mechanism, built a good foundation for the applicability of the reaction. In the way of intramolecular rotation characteristics to develop a new material synthesis method basing on supramolecular chemistry concept is the features and innovations of this dissertation.