Design, synthesis and characterization of new electron acceptors and materials based on 4,5-dicyanoimidazole and 4,4',5,5'-tetracyano-2,2'-biimidazole.
Apen, Paul Gregory
1990
Abstract
Several methods for functionalizing 4,5-dicyanoimidazoles have been developed. Nucleophilic aromatic substitution (NAS) on 1-methyl-2-bromo-4,5-dicyanoimidazole with piperidine, morpholine, imidazole, cyanide and other nucleophiles gives the corresponding 1-methyl-2-substituted-4,5-dicyanoimidazoles. NAS with 4-dimethylaminopyridine or pyridine gives novel betaine or internal salts. Reaction of 1-methyl-2-bromo-4,5-dicyanoimidazole with poly(4-vinylpyridine) gives the pyridinium-dicyanoimidazolate internal salt substituted along the polymer backbone. The structural, thermal and viscosity characterization of the substituted polymer(s) is described. Conditions for selective metallation of 1-protected-4,5-dicyanoimidazoles is described. Various protecting groups were used. Reaction of 1-methyl-2-lithio-4,5-dicyanoimidazoles with electrophiles gives low yields of 2-substituted products. Oxidative coupling of 1-protected-2-lithio-4,5-dicyanoimidazoles with cupric chloride gives new 1,1'-derivatives of 4,4',5,5'-tetracyano-2,2'-biimidazole (R$\sb2$Tcbiim where R = $\rm CH\sb3, CH\sb2OCH\sb3, CH\sb2Ph$). Ullmann coupling of 1-methyl-2-bromo-4,5-dicyanoimidazole gives Me$\sb2$Tcbiim. Deprotection of R$\sb2$Tcbiim (R = $\rm CH\sb3, CH\sb2OCH\sb3$) gives 4,4',5,5'-tetracyano-2,2'-biimidazole (H$\sb2$Tcbiim). Several new routes to H$\sb2$Tcbiim are now available. Reaction of H$\sb2$Tcbiim with dihaloalkanes gives 1,1'-alkyl bridged derivatives of Tcbiim. Intramolecular Ullmann coupling reactions give good yields of 1,1'-dimethylene Tcbiim, or (CH$\sb2$)$\sb2$Tcbiim. The chemistry and reactivity of H$\sb2$Tcbiim and its derivatives were studied. The physical, structural and electronic properties of these new cyanomidazoles have been investigated using UV-visible spectroscopy and cyclic voltammetry. (CH$\sb2)\sb2$Tcbiim forms a 1:1 adduct with tetrathiafulvalene(TTF). The donor(D)-acceptor(A) complex forms as red needles from acetonitrile. X-ray diffraction of the crystal shows extended alternate or "mixed" stacking (....DADADA...). Luminscence spectroscopy on the solid shows an emission band centered at 660nm. The onset of emission at 530nm is consistent with charge-transfer absorption in the blue region of the visible spectrum and the resulting red color of the donor-acceptor complex. Dehalogenation reactions of 1,2-dihalo-4,5-dicyanoimidazoles (IBrDcim or I$\sb2$Dcim) give materials with novel elemental compositions and high carbon and nitrogen contents. At 200$\sp\circ$C in air, pyrolysis of IBrDcim or I$\sb2$Dcim gives low molecular weight materials of ($\rm C\sb5N\sb4$) $\sb{\rm x}$ composition. At 300$\sp\circ$C in air, complete dehalogenation of IBrDcim occurs and a black glass with the empirical formula ($\rm (C\sb{10}N\sb9)\ \cdot\ 2H\sb2O$) $\sb{\rm x}$ remains. These materials exhibit high thermal stability and low flammability. The thermal and structural characterization of the monomers and polymers are described.Other Identifiers
(UMI)AAI9116114
Subjects
Chemistry, Organic Chemistry, Polymer
Types
Thesis
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