Water-soluble Conjugated Polymer Light-emitting Materials

The dissertation is related to light-emitting materials based on conjugated polymers. Since the 1990's,light-emitting conjugated polymers have attracted much interest owing to their wide-ranging application potential in the development of polymer light-emitting diodes.And in the late 1990's,water-soluble conjugated polymers conjugated polyelectrolytes became new highlights.At our research group,our long-term interest focuses on conjugated polymers,and we are also interested in the investigation on conjugated polyelectrolytes.To prepare water-solubleÏ€-conjugated polymers,the use of conventional synthetic chemistry via covalent bonding interactions is complex,tedious and time-consuming.The ordered nanostructures arising from the supramolecular assembly via noncovalent bonding interactions offer a simple and convenient method to prepare the alternative water-soluble conjugated materials,which will reserve the corresponding optical properties of theÏ€-conjugated polymers and can be good replacers for them.Recently,our interests lie in some new approaches to macromolecular assembly ofÏ€-conjugated polymer blends in water especially by noncovalently bonded self-assembly.Based on our early work related to conjugated polymers,we have mainly been engaged in the research works as following:In chapter 2,a series of amino-functionalized phenyl-substituted poly(p-phenylenevinylene)(PPV) related copolymers were synthesized by Wittig reaction. Their corresponding cationic conjugated polymers were successfully obtained via a post-polymerization approach.On the basis of FT-IR and ¹H NMR spectra,it was found that phenyl-substituted PPV related copolymers containing alkoxylated benzene(neutral polymer P1 and quaternized polymer P1'),phenylated benzene(neutral polymer P2 and quaternized polymer P2') and fluorene(neutral polymer P3 and quaternized polymer P3') moieties are of 55%,80%,and 45%cis-vinylic linkage respectively while the polymer containing thiophene moiety(neutral polymer P4 and quaternized polymer P4') is primarily of trans-vinylic linkage.Their photoluminescence(PL) were conveniently tuned from blue color to yellow color by introducing units with different optoelectronic properties into the PPV backbones.The polymer with fluorene unit and bulky phenylene-substituted benzene unit in the backbone exhibited the highest PL efficiency among these neutral and quaternized PPVs. In chapter 3,we studied the quenching effect of Fe(CN)₆^4- on cationic PPV derivatives with cis- and/or trans-vinylic linkage.Downward Stern-Volmer curves were found in PPVs with cis-/trans-vinylic linkage while upward Stern-Volmer curves in PPVs with all trans-vinylic linkage.Electron transfer,not energy transfer,was the major way to result in quenching of PPVs with cis-linkage and those downward curves presented the incomplete quenching from inaccessible fluorophore.After considering the inaccessible fluorophore and sphere-of-action effect,a modified Stern-Volmer equation was obtained to well fit the downward Stern-Volmer curve of PPVs with cis-linkage.The cis-vinylic linkage and the bulky side groups were considered to be the major factor to produce such inaccessible fluorophore.In chapter 4,a new water-soluble cationic ammonium-functionalized poly(p-phenylenevinylene)(PPV-NEtMe₂⁺) was successfully synthesized via Glilch method and this cationic conjugated polymer exhibited highly sensitivity on rubredoxin,an anionic ET protein.Further investigation showed that the biosensitivity of the cationic conjugated polymer is strongly dependent on the nature of the buffer solution and the concentration of the conjugated polymer used in the analyses.Considering the important role of iron-sulfur centered Rd as an ET relay in vivo and the efficient fluorescent quenching of cationic conjugated polymers observed here,our results afforded new opportunities for potentially greatly improved PPV-based biosensors.In chapter 5,we have successfully induced the formation of strawberry-like nanoparticles based on the interpolymer hydrogen-bonding interactions between P(FOH) and PGAL.In the aqueous solution of the nanoparticles the conjugated polymers formed a unimolecule structure and the primary optical properties of them in THF still remained.The strawberry morphologies observed in the new water-soluble nanoparticles are different from that of our previous work,which is probably related to the hydroxyl contents.A more comprehensive study is necessary to explain this difference and understand the photophysical properties of single conjugated polymer chains.These carbohydrate-functionalized assemblies of fluorescent polymers may be used to detect some bacteria,which is also our future work.