Snythesis And Properties Of Extended Conjugated Structure Of Boron-Nitrogen Aromatic Hydrocarbons

Boron(B)and nitrogen(N)are adjacent elements to carbon(C)in the periodic table.The difference in electronegativity leads to significant differences in electronic structure,self-assembly behavior and delocalization resonance between BN hetero and traditional PAHs.Especially,BN unit,as an isoelectronic body with CC double bond,can be used to construct conjugated structures,which are similar to that of carbon molecules but with different physical properties.BN embedded PAHs have broad prospects in organic electronics,such as organic light emitting diodes(OLEDs),organic field effect transistors(OFETs)and organic photovoltaic(OPVs).So far,the reported BN embedded PAHs were mainly synthesized via the electrophilic substitution or addition reaction Electrophilic substitution or addition reaction by boron Lewis acid,and,the nitrogen atom were used as the orientation to realize the intramolecular ring closing reaction.The leaving group was often needed to enhance the regioselectivity and electrophilic reaction activity of the ring closing.These limit the expansion of molecular structures and hinder the systematic understanding and in-depth study of the functions of these molecules.In addition,the post-functional modification of BN embedded PAHs molecular structure is very limited,which also affects the diversification of molecular structure extension.For example,NB embedded polymers are still rare.A variety of effective synthesis strategies were established to obtain novel BN embedded PAHs with extended conjugated structure from small molecules to polymers,and their photoelectric properties were systematically studied.Furthermore,the applications of these molecules in electroluminescence and chemical sensors were preliminarily explored.The dibenze[a,j]anthracence derivatives were synthesized via intramolecular bronsted acid induced phenylalkynyl cyclization.By extending the conjugated structure of the precursor,the regioselectivity and activity of the electrophilic substitution of aromatic ring molecules can be improved effectively.A series of heteropolycyclic aromatic hydrocarbons with NBN units embedded in the molecular skeleton were prepared by intramolecular C-H-activated electrophilic cyclization of boron.The photophysical and electrochemical behaviors of these molecules,as well as the strong blue-green fluorescence properties,were revealed.The electroluminescent devices with these molecules as the light-emitting layer showed low starting voltage and strong luminescence characteristics(the brightness 8095cd/m~2).The 6,8-diiododibenz[a-,j]anthracenes derivatives were synthesized via iodine chloride(ICl)activated intramolecular phenylalkynyl cyclization.A series of heteropolycyclic aromatic hydrocarbons with NBN units embedded in the molecular skeleton were prepared by nitro reduction and intramolecular C-H activated electrophilic cyclization of boron.Furthermore,a series of NBN embedded PAHs derivatives with extended conjugation structure were prepared by using transition metal catalyzed coupling reaction.The accurate structure of these molecules was determined by single crystal.The spectra and showed that these molecules exhibits rich semiconductor activity.A series of alternating conjugated polymers containing NBN embedded PAHs were prepared via suzuki coupling copolymerization of key functional monomers(NBN embedded PAHs)with various boric acid/borate ester substituted(hetero)aromatic derivatives.The semiconductor properties of conjugated polymers can be precisely controlled by introduction of different comonomers.For example,the introduction of strong electron-withdrawing unit can effectively reduce the band gap of polymer.At the same time,the electron-withdrawing monomer can also reduce the charge density around boron atom and improve its Lewis acidity.Therefore,the polymer exhibited polarity dependent reversible fluorine ion response and color change behaviors,and can be used as colorimetric method to identify halogenated and non halogenated solventsA series of amino substituted alternating conjugated polymers with2,5-dibromo-1,4-diphenylamine derivatives as key monomers were prepared via stille coupling copolymerization catalyzed by transition metals.A series of BN embedded lader-type polymers were synthesized via B-N lewis acid base pair directed continuous boron-nitrogen condensation and direct C-H activated electrophilic cyclization of boron.The~1H NMR clearly revealed that these polymers have the characteristics of aromatization and less junction defects.The band gap of these kind of these polymers can be adjusted introduction of different comonomers,and shows higher thermal stability compared with non fully condensed conjugated polymer(decomposition temperature>382℃),narrow emission half peak width,high quantum yield and long fluorescence lifetime.