Synthesis And Characterization Of A Novel Azo-containing Polymer Both In Main-and Side-chain With Photocontrolled Isomerization By UV-Visible Light

In recent years,azo-containing polymers have attracted much attention due to the unique physical and chemical properties and reversible optical response characteristics.The researchers have reported many side-chain azo-containing polymers.Recently,researchers have also reported some work on main-chain azo-containing polymers.However,the reversible trans-cis photoisomerization of azo group in these azo-containing polymers were generally photoinduced by irradiation with UV light.More recently,visible light-driven photoisomerization of azo-containing polymers has attracted great attentions.At the same time,it was also possible for us to design and synthesize a full wavelength(from UV to visible)light-driven photoisomerization of azo-containing polymers,that is,the introduction of two kinds of azo groups by irradiation with UV/visible and visible/visible light-driven reversible trans-cis photoisomerization into one polymer chain.The photoisomerization of azo groups in polymers was achieved by irradiation with different wavelength light.In this thesis,we have synthesized a series of azo-containing polymers with different topological structures via Suzuki polycondensation reaction.And their photoisomerization behaviors were also investigated.The detailed results were summarized as following:(1)In this work,we mainly studied the photocontrolled trans-cis structural changes of both side-chain and main-chain azo-containing polymer by irradiation with UV-visible light,which has not been reported in the previous literature.Firstly,we prepared two functional monomers containing fluorene and fluorenazobenzene with bromide substituents at both ends and bifunctional azobylate.Then,we used Suzuki polycondensation reaction to prepare azo-containing polymers,such as poly[(9,9-di(4-methoxyazobenzene-4-oxy)octylfluorenyl-2,7-diyl)](AZOF8),poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-4,4'-azobenzene](F8-alt-AZO)and poly[(9,9-di(4-methoxyazobenzene-4-oxy)octylfluorenyl-2,7-diyl)-alt-4,4'-azobenzene](AZOF8-alt-AZO).Firstly,we studied the synchronous and cross isomeric changes of the single-azobenzene at main-chain of F8-alt-AZO and the single-azobenzene at side-chain of AZOF8 by irradiation with same wavelength light.We found the differences between the two types of trans-cis reversible structure changes by comparison.Then we selected the appropriate wavelength to selectively control trans-cis structural changes of azo groups of AZOF8-alt-AZO in the light-driven process.We have developed two light-driven methods to control trans-cis structural changes of azo groups in AZOF8-alt-AZO.The first one was the utilization of light wavelength at 365 nm,435 nm and 546 nm in order.Firstly,side-chain azo group of AZOF8-alt-AZO underwent the trans-to-cis isomerization and main-chain azo group of AZOF8-alt-AZO underwent no isomerization upon irradiation with UV light wavelength at 365 nm(Side-chain Cis-Main chain Trans,SC-MT).Secondly,side-chain azo group of AZOF8-alt-AZO underwent the cis-to-trans isomerization and main-chain azo group of AZOF8-alt-AZO underwent trans-to-cis isomerization upon irradiation with blue light wavelength at 435 nm(Side-chain Trans-Main chain Cis,ST-MC).Finally,main-chain azo group of AZOF8-alt-AZO underwent the cis-to-trans isomerization upon irradiation with green light wavelength at 546 nm and side-chain azo group of AZOF8-alt-AZO underwent no isomerization(Side-chain Trans-Main chain Trans,ST-MT).In this light-driven process,we successfully controlled the reversible cis-trans structure changes and obtained three different structural polymers(SC-MT,ST-MC and ST-MT).We optimized the method in order to obtain the other different structural polymers.The second one was the utilization of light wavelength at 313 nm,405 nm,435 nm and 546 mm in order.Firstly,side-chain azo group of AZOF8-alt-AZO underwent the trans-to-cis isomerization and main-chain azo group of AZOF8-alt-AZO underwent no isomerization upon irradiation with UV light wavelength at 313 nm(ST-MC).Secondly,both side-chain and main-chain azo groups of AZOF8-alt-AZO underwent the trans-to-cis isomerization simultaneously upon irradiation with blue purple light wavelength at 405 nm(SC-MC).Thirdly,side-chain azo group of AZOF8-alt-AZO underwent the cis-to-trans isomerization and main-chain azo group of AZOF8-alt-AZO underwent no isomerization upon irradiation with blue light wavelength at 435 nm(ST-MC).Finally,main-chain azo group of AZOF8-alt-AZO underwent the cis-to-trans isomerization and side-chain azo group of AZOF8-alt-AZO underwent no isomerization upon irradiation with green light wavelength at 546 nm(ST-MT).In this light-driven process,we successfully controlled the cis-trans photoisomerization and obtained polymers with different structural trans and cis Azos in the same polymer chain.(2)In the previous chapter,the absorption band intensity of the cis-isomers of the main-chain azo group of AZOF8-alt-AZO was too weak to control their photoisomerization behaviour by irradiation with different wavelength light.Therefore,we introduced four fluoro groups into the main-chain ortho-azobenzene to enhance the absorption intensity of cis-isomer of main-chain azo group in polymer chain.We studied the reversible cis-trans photoisomerization of alterning copolymer with the main-chain tetrafluoroazo side-chain azo groups under irradiation with different wavelength light.Firstly,we prepared two functional monomers containing fluorene and fluorenazobenzene with bromide substituents at both ends and bifunctional borate and o-fluorine azobenzene bifunctional boric acid ester.Furthermore,we used Suzuki polycondensation reaction to prepare azo-containing polymers such as poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-4,4'-o-terafluroazobenzene](F8-alt-o-FAZO)and poly[(9,9-di(4-methoxyazobenzene-4-oxy)octylfluorenyl-2,7-diyl)-alt-4,4'-o-terafluroazobenzene](AZOF8-alt-o-FAZO).Firstly,we studied the synchronous and cross isomeric changes of the single-azobenzene at main-chain o-terafluroazobenzene group of F8-alt-o-FAZO and the single-azobenzene at side-chain azo group of AZOF8 by irradiation with same wavelength light.We found the differences between the two types of trans-cis photoisomerization by a detailed comparison.Then we selected the appropriate wavelength light to selectively control own trans-cis photoisomerization of two kinds of azo groups of AZOF8-alt-o-FAZO,to obtain several different structural polymers in the light-driven process.Finally,we developed a light-driven way to control trans-cis photoisomerization of AZOF8-alt-o-FAZO.The light-driven way was the utilization of light wavelength at 546 nm,365 nm and 435 nm in order.Firstly,main-chain o-terafluroazobenzene group of AZOF8-alt-o-FAZO underwent the traps-to-cis isomerization and side-chain azo group of AZOF8-alt-o-FAZO underwent no isomerization upon irradiation with green light wavelength at 546 nm(ST-MC).Secondly,main-chain o-terafluroazobenzene group and side-chain azo group of AZOF8-alt-o-FAZO underwent the trans-to-cis isomerization simultaneously upon irradiation with UV light wavelength at 365 nm(SC-MC).Finally,main-chain o-terafluroazobenzene group and side-chain azo group of AZOF8-alt-o-FAZO underwent the cis-to-trans isomerization simultaneously upon irradiation with blue light wavelength at 435 nm.In this light-driven process,we successfully controlled the cis-trans structural changes and obtained three different structural polymers.We successfully overcame the drawback of slight cis-trans photoisomerization of main-chain azo group as reported in previous chapter.