Synthesis And Properties Of Novel Polyaryls

Currently,polyaryls are materials of considerable interest for chemists,physicists, and material scientists,which are found at the core of a wide variety of interesting organic molecules,ranging from pharmaceutical agents,liquid-crystalline molecules, pesticides,dyes,nano-matefials to OLED materials.Polyaryls,which contained functional groups such as nitro group and thiol group,have been the focus of intense research because of their interesting optical and electrical properties.For instance, polyaryls containing nitro group could be transformed to polyindolocarbazole and polydiindolocarbazole,which showed good optical and electrochemical properties. Polyaryls containing thiol group can form self-assembled monolayers(SAMs) on the surface of Au,Ag or other metals.SAMs plays an important role in the construct ordered nanostructure in molecular electronics.Substituting conjugated organic thin-film-based electronic devices can be used in light-emitting devices,organic negative resistance devices,molecular circuit components and ultra-micro-chip, ultra-high density information records technology,and so on.Now,the main synthetic methods of polyaryls were cross-coupling reaction.Thirty-nine novel polyarylenes were synthesized using Suzuki cross-coupling reaction and Sonogashira cross-coupling reaction catalyzed by palladium.Their structures were characterized by IR,NMR,EA and HRMS.The ultraviolet absorption spectra and fluorescence spectra were investigated and the relationship between molecular structure and spectra properties were studied.The thermal properties were tested by thermo-gravimetric analysis(TGA) and the electrochemical properties were investigated by cyclic voltammetry(CV).The geometric molecular structures were calculated by the software of Gaussian 03 and the corresponding HOMO and LUMO energies were optimized using the density functional theory(DFT) with correlation functional(B3LYP) and the 3-21G basis set.Seventeen novel unsymmetrical terphenyls with nitro group and methylthio group were prepared in good yields by regio-selective double Suzuki cross-coupling reaction which employed Pd(PPh₃)₄ as catalyzer,K₂CO₃ as base and 1,2-dimethoxyethane (DME) as solvent.4-Bromo-1-iodo-2-nitrobenzene react with 4-(methylthio)phenylboronic acid to give single cross-coupling product of (4'-bromo-2'-nitrobiphenyl-4-yl)(methyl) sulfane(3) in high yields,which then reacted with various boronic acids to give unsymmetrical terphenyls of(4a-q).The ultraviolet absorption and fluorescence properties of these compounds were recorded in CHCl₃.It was found that UV-vis maximal absorption spectra were in the range of 241～318 nm.Theλ_abs^max of 4"-formyl-4-methylthio-2'-nitro- 1,1 ',4',1"-terphenyl(4j) was 299 nm and gave a larger red shift than other unsymmetrical terphenyls. Introducing heterocycles(such as thiophene,benzothiophene) showed a large red-shifted absorption compared with unsymmetrical terphenyls.The largest red shift (λ_abs^max = 318 nm) occurred when benzothiophene is introduced to the compounds. These compounds showed good thermal stabilities(＞200℃) as determined by thermo-gravimetric analysis(TGA).From the figure of cyclic voltarnmetry(CV) we can see that the compounds show two obvious reduction curve and the first reduction curve(reduction potential is -1.22 V) is quasi-reversible.Four novel functional symmetrical oligophenylenes(7a-d) are prepared by Pd(PPh₃)₄ catalyzed double Suzuki cross-coupling reaction from 1,4-bis(4,4,5, 5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene and substituted 4-bromo-2-nitrobiphenyls(6a-d) in DME with K₂CO₃ as base in 44-75%yields. Four novel functional symmetrical oligoarylenes bearing heteroaryl group(9a-d) are prepared by Pd(PPh₃)₄ catalyzed double Suzuki cross-coupling reaction from 2, 5-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophene and substituted 4-bromo-2-nitrobiphenyls in 1,4-dioxane with Caesium fluoride(CsF) as base in 30-80%yields.Substituted groups had a great effect on spectral properties.It was found that UV-vis maximal absorption spectra of 7a-d were in the range of 295～307 nm.Introducing electron donating group caused bathochromic shift of the absorption maximum and the sequence were H(7a)＜Et(7b)＜OMe(7c)＜SMe(7d).The UV-vis maximal absorption spectra of 9a-d were in the range of 343～348 nm.Introducing electron donating group also caused bathochromic shift of the absorption maximum and the sequence were H(ga)＜Et(9b)＜OMe(9c)≈SMe(9d).Introducing heterocycles caused bathochromie shift compared maximal absorption spectra of 7a-d with 9a-d. These compounds show good thermal stabilities as determined by TGA and the temperature of losing 5%weight is above 200℃.Cyclic voltammetry(CV) of the synthesized compounds show two obvious reduction curve and the first reduction curve(reduction potential is -1.22 V) is quasi-reversible.Fourteen novel OPEs derivatives are prepared by convergent synthetic methodologies that are based on Suzuki and Sonogashira cross-coupling reaction for aryl-aryl and aryl-ethynyl bond formations.Firstly, ((4-bromo-2-nitrophenyl)ethynyl)trimethylsilane(10) reacted with substituted phenylboronic acid to furnish compounds 11a-m.Reactions was carried out using tetrakis(triphenylphosphine) palladium(0) as catalyst and potassium carbonate(K₂CO₃) as base in 1,2-dimethoxyethane(DME) and H₂O at reflux temperature.Then compounds 11a-m were desilylated using tetrabutylammonium fluoride(TBAF) to furnish the terminal alkynes 12a-m.Secondly,OPEs derivatives 14a-m can readily be achieved by reaction of the corresponding terminal alkynes 12a-m with S-4-iodophenyl ethanethioate(13) using palladium catalyzed Sonogashira cross coupling reaction.Reactions was carried out using tris(dibenzylideneacetone)dipalladium(0) as catalyst,copper(â… ) iodide as co-catalyst and triphenyl phosphine as ligand with N,N-diisopropylethylamine as base.The synthetic route of 17 was similar to 14a-m.It was found that UV-vis maximal absorption spectra of 14a-m and 17 were in the range of 304～321 nm.Introducing substituted groups both electron-donating(R= F,CF₃,C1,CN,acetyl,formyl,vinyl) and electron-withdraw groups(R= methoxy,thiomethyl,ethyl,2,5-dimethoxy) caused bathochromic shift except 14a(R=2,3-dimethoxy) which caused hypsochromic shift.It was found that the largest UV-vis maximal absorption wavelength was 321 nm when R was methylthio group.These compounds show good thermal stabilities as determined by TGA and the temperature of losing 5%weight is above 200℃.Cyclic voltammetry(CV) of the synthesized compounds show two obvious reduction curve and the first reduction curve(reduction potential is -1.10 V) is quasi-reversible.