Synthesis Of Monodisperse Oligoanilines And Their Properties

Conjugated polymers (e.g., polyacetylenes, polythiophenes, polyanilines etc.)exhibit interesting properties for the development of lightweight batteries,electrochromic display devices, light-emitting diodes, optical switches, etc. However,these conjugated polymers like conventional polymers, have distribution ofmolecular weight, conjugated length and structure defects. The properties of theconjugated polymers are therefore the statistic averages of each structure. Thisrenders the difficulty of controlling properties of materials through tailoring of theirmolecular structure. By comparison, monodisperse conjugated oligomers,characterized by step-by-step increasing size of the π-system, can establish detailedstructure-properties relationship for their corresponding polymers. On the other hand,monodisperse conjugated oligomers could also act as excellent materials, becausestudies on the conjugated oligomers have revealed that the covergence limit ofoptical and electronic properties of many conjugated polymers [e. g.,poly(p-phenylenevinylene)s, ladder-type poly(p-phenylene)s, polythiophenes andpolyanilines] is already reached for oligomers containing only a few repeat units. In this thesis, we synthesized a series of monodisperse oligoanilnes and theproperties of these oligoanilines were studied. The thesis could be summarized asthe points shown below:1. One-step oxidative coupling reaction to synthesize parent anilinepentamer and hexamer Parent aniline pentamer and hexamer have been synthesized successfullythrough a novel method (oxidative coupling reaction), and were characterized by IR,MALDI-TOF-MS, elemental analysis and 1H-NMR. The chemical oxidation processof the pentamer and hexamer were studied by UV-Vis spectra. It was found thepentamer and hexamer were oxidized to EB form and then to the pernigranilineoxidation state.2. synthesis of amino-capped aniline tetramer and pentamer by themethod of amino terminal group protection Amino-capped aniline tetramer and pentamer were synthesized successfullythrough a novel method, this synthetic route protected the amino terminal group ofN-phenyl-1,4-phenylenediamine from further reaction. The tetramer and pentamerwere characterized by IR and MALDI-TOF-MS. The chemical oxidation process ofthe tetramer and pentamer were studied by UV-Vis spectra. It was found the(tetramer) pentamer was oxidized to its EB form and then to the pernigranilineoxidation state.3. Simple oxidative coupling reaction to synthesize phenyl-cappedaniline heptamer A convenient method has been reported for the synthesis of phenyl-cappedaniline heptamer. The method was accomplished by the reaction of parent anilinepentamer in the pernigraniline oxidation state withN,N-diphenyl-1,4-phenylenediamine in the leucoemeraldine oxidation state. Thephenyl-capped aniline heptamer in the leucoemeraldine oxidation state wascharacterized by IR, H-NMR, MALDI mass spectra and elemental analysis. Its 1chemical oxidation process was studied by UV-Vis spectra and the electrochemicalanalysis was studied by CV. It was found that the phenyl-capped aniline heptamershowed three oxidative waves in the cyclic voltammetry, different from polyaniline.We believed that the second peak was due to the occurring of nigraniline form.Phenyl-capped aniline heptamer in the EB state was synthesized and studied byUV/Vis spectra. We found the relative amount of amine and imine groups in theoligoanilines in the EB state bear the following relation with the ratio of the intensityof band a (π-π* transition) to the intensity of band b (exciton peak transition) mimine Intensityratio mimine + mamine Intensityratio stand for the ratio of the intensity of band b to that of band a. mamineis the amount of amine atom in the aniline oligomer in the EB state. mimine is theamount of imine atom in the aniline oligomer in the EB state. The intensityratio ofheptamer in the EB state equals to 0.27, so we considerd the heptamer in the EBstate only contain one quinoid ring4. The properties of oligoanilines The effect of chain length on position of excitonic peak was studied forphenyl-capped aniline oligomers and parent polyanilineamino-capped anilineoligomers. It was found that the λmax of exciton peak increased with the increase ofchain-length for the oligomers. However, the increasing rate of phenyl-cappedaniline oligomers was much faster than that of parent aniline oligomers. Obviously,end-groups have an extremely important effect on the properties of aniline oligomers.For phenyl-capped oligoanilines, it needs only eight repeat units to reach the sameλmax (exciton peak) as in polyaniline (250 repeat units). The λmax (599nm, measured...