Synthesis And Structure-Property Relationship Study Of Fluorene Based Conjugated Polyelectrolytes/Polymers

Conjugated polymers are a novel class of materials that combine the optical and electronic properties of semiconductors with the attractive mechanical properties and processing advantages of polymers. These days, conjugated polymers have been widely used in optoelectronic devices and sensors. Conjugated polyelectrolytes (CPEs) are polymers that contain aπconjugated backbone and functional groups that ionize in high dielectric media. Because of combining the semiconducting and light harvesting properties characteristic of electronically delocalized polymers with the charge-mediated behavior of polyelectrolytes,conjugated polyelectrolytes exhibit some unique properties and functionalities as compared with neutral conjugated polymer, and thus become more and more attractive in recent years. Because the properties of conjugated polymers can be fined-tuned by manipulation of their chemical structures, considerable research efforts have been directed towards the preparation of well-defined conjugated polymers. This thesis mainly focused on the design and synthesis of novel conjugated polyelectrolytes/polymers. On one hand, we aimed on increasing the water solubility of conjugated polyelectrolytes and adjusting conjugated polyelectrolytes properties by modification of the structure. On the other hand, we designed and synthesized several conjugated polymers/oligomers with functionalized groups on the side chains which can combine a fluoride ion and form conjugated polyelectrolytes. By application of this property, these polymers can be used for fabrication of chemically fixed p-n junction polymer semiconducting bilayers.Conjugated polyelectrolytes (CPEs) presumably tends to come together and aggregate to minimize exposure of the backbone to polar solvent such as water due to the extremely hydrophobic nature of the conjugated backbone. Lots of reported conjugated polyelectrolytes behave with low solubility and low fluorescence in water, which badly limited their applications. So it is most important to design and synthesize water-soluble conjugated polymers with high solubility. By introducing high charge density to the side chains of the polymer and adopting appropriated side chain length, we synthesized a water soluble conjugated polymer with excellent water solubility up to 100 mg ml-1 as well as high PL quantum yield of 44% in water. The standard NPB/Alq3 device using this polyelectrolyte as the electron injection layer shows nearly 3 times enhancement in the EL efficiency. Through controlling of the reaction time we have synthesized a series of conjugated polyelectrolytes with different quaternization degrees. The relationships of the solubility and the PL quantum yield with the quaternization degree have also been demonstrated. AFM was used to investigate the aggregation behavior of the polyelectrolytes in films. By rational incorporation of functional group-bipyridyl to the conjugated backbone, we have prepared a series of fluorene based bipyridine containing water soluble conjugated polymers. The aqueous solution behavior and ion responsive properties of these polyelectrolytes were studied.In LECs, the ion motion that is required for the operation of these devices leads to long temporal responses and a dynamic electronic structure. So, the development of new materials and new methods to fix the ions is desirable. We designed and prepared a new conjugated polymer PFP-BMes which composed of poly (fluorene-co-phenylene) PFP conjugated backbone and dimesitylboron functionality attached to its side chains. The dimesitylboryl group in PFP-BMes can be modified by a fluoride source in solution, and thus form a polyelectrolyte. A permanently-fixed organic p-n heterojunctions can thus be achieved by using this polymer with dimesitylboron functionality (anion-trapping functional groups) and an uplayer of a cationic conjugated polyelectrolyte (CPE) with fluoride counteranions. The devices show no delay in the turn on of light-emitting electrochemical behavior and excellent current rectification.The ionic conducting polymer poly(ethylene oxide) (PEO) is usually used to facilitate the ion motion in a typical LECs. However, due to the polarity difference of the PEO and the EL polymers, phase separation between these two polymers occurs as they mixed together, which can significantly degrade the device performance. In order to solve this problem, we sought to incorporate short PEO chains into dimesitylboryl functionality containing conjugated polymers. However, the desired polymer encountered a solubility problem. Different synthetic strategies were tried and a variety of polymer structures were designed to make this kind of polymer soluble. Finally, by rational incorporation of a unit with branched structures, we got a conjugated polymer with very good solubility. To better understand the relationship between the property and structure of this kind of polymers, we synthesized an oligomer combining both of the functionalities, and studied its optical properties and thermal properties.