Reaction Activity And Stabilizing Of The P-quinodimethane Intermediates And Their Application

During the past decades, considerable attention has been focused onp-quinonoid intermediate and its derivatives. A large and important class ofreactive molecules such as substituted p-quinodimethanes, and p-quinodimethanesderivates based on other aromatic systems including naphthalene, anthracene,furan and thiophene have been prepared by a number of different methods. Itshigh reactivity and unique structure have attracted the interests of organicchemists and quantum chemists. An explosive amount of activities in the area ofthe quinoid chemistry has been developed in a variety of fields such as their use asbuilding blocks in the synthesis of organic and polymeric materials, materialsscience, fullerene chemistry and electrochemical studies.In the first section of Chapter 1, we reviewed the reaction activities andpolymerizations of p-quinonoid intermediates, including the polymerizationmechanism of the p-quinodimethane intermediates in solution. In the secondsection, we describe several synthetic routes which have been developed toincrease the solubility of PPV and modify its luminescent properties. In the lastsection, we reviewed the synthesis and properties of conjugated quinoidcompounds and polymers.In Chapter 2, we developed a novel copolymerization betweenp-quinodimethane active intermediates and vinyl monomers by adding styrene toa reaction performed via the typical chlorine precursor route toward the synthesisof poly(p-phenylene vinylene) (PPV). The copolymerization mechanism andproperties of the resultant copolymers were investigated. In the presentcopolymerization, the p-quinodimethane intermediate acts as both initiator andmonomer, which is quite different with traditional free-radical copolymerizationbetween two vinyl monomers. A new family of conjugated/nonconjugatedcopolymers are synthesized by copolymerization between p-quinodimethaneactive intermediates and styrene. The resulting copolymers show improvedsolubility and blue-shifted photoluminescence as compared with thecorresponding PPV derivatives. The composition, structure andphotoluminescent(PL) properties of the obtained copolymers can be adjusted bythe feed ratio of the two monomers. A series of amphiphilicconjugated/nonconjugated copolymer was synthesized also by copolymerizationbetween p-quinodimethane active intermediates and acrylic acid. In Chapter 3, the self-assembly behaviors and luminescent properties of thecongjugated/nonconjugated copoymers were investigated. It was found that theamphiphilic conjugated/nonconjugated copolymers poly(2,5-dimethoxy-p-phenylenevinylene-co-Acrylic acid) could form nanospheres or multiphasenanostructures in water or selective solvents, which indicated the novelamphiphilic copolymers can be used as building blocks for supramolecularself-assembly. High performance green-yellow light copolymer electroluminescent deviceshave been fabricated by using a soluble copolymer material,poly(2,5-dimethoxy-p-phenylenevinylene-co-styrene) (DMeO-PPV-co-PS). Abilayer device of configuration ITO/DMeO-PPV-co-PS/BBOT/Al exhibited amaximum luminance of 1550 cd m-2 and a turn-on voltage of 6.2 V. Comparedwith the single-layer copolymer device ITO/DMeO-PPV-co-PS/Al, the turn-onvoltage decreases from 13.0 to 6.2 V and the maximum luminance increases from230 cd m-2 to 1550 cd m-2. The incorporation of both biphenyl group and nonconjugated polystyrenesegments into the main chain of the copolymer can modify the band structure andmolecular conformation, which might induce torsion of the main chain andconsequently reduce the planarity of the copolymer. All these can lead toshortening of the effective conjugation length and result in a blue shift in PLemission. Blue light emission with a maximum at 457 nm and a turn-on voltage of9.0 V were observed from a single-layer device of solublepoly(p-biphenylenevinylene-co-styrene) copolymer in which the copolymer wasused as an emitting material. Electroluminescent studies show that theseconjugated/nonconjugated copolymers are suitable materials for the preparation ofpolymeric LEDs. In Chapter 4, we developed a convenient method to prepare new conjugatedquinoid compounds containing electron-poor oxadiazole aromatic units bystabilizing the oxadiazolequinodimethane intermediates. By incorporation ofelectron-poor oxadiazole aromatic units into π-conjugated system, a series ofnovel quinoid compounds were synthesized and their structures werecharacterized by means of elemental analysis, H-NMR, ESR and mass spectrum. 1The relationship between the chemical structures of the conjugated quinoidcompounds and reaction activities were investigated. Our experimental resultsshowed that incorporation of electron-poor aromatic ring in the quinoid structureand tert-butyl benzene in each side of the quinoid structure could keep highthermal and chemical stability while still achieving small band-gap and high...