IMINE-BRIDGED PLANAR POLY(P-PHENYLENE) DERIVATIVES FOR MAXIMIZATION OF EXTENDED PI-CONJUGATION - THE COMMON INTERMEDIATE APPROACH

Described are two approaches to planar conjugated poly(p-phenylene) (PPP) derivatives. The first approach, involving lactam bridges, was unsuccessful due to the insolubility of the 6(5H)-phenanthridinonyl moieties. The second approach, which utilized imine bridges, worked excellently since the compounds were generally soluble and the bridge formations were highly efficient. The main PPP backbone was synthesized via Pd(0)-catalyzed coupling of an arylbis(boronic ester) with an aryl dibromide. Imine bridges, which are formed by exposure of the polymer to trifluoroacetic acid or HCl, force the consecutive units into planarity. The bridging units are sp(2) hybridized, thus allowing for greater pi-electron flow between the consecutive phenyl units. The polymers, upon planarization, exhibit enormous bathochromic shifts of 210-240 nm. The optical spectra of the planar systems are compared to that of the parent nonplanarized polymers, oligo(p-phenylenes), and PPP. When the bridges were n-dodecyl- or n-octylphenyl-substituted, the fully planar structures could be made into flexible free-standing films. Additionally, an improved method is described in which a common intermediate, an aryl dibromo diacyl halide, could be used to prepare both the A and B units for the AB-type step growth polymerization. In one case, a selective alkylation or arylation of the acyl portions was accomplished using lower order cyanocuprates or Pd(0)-catalyzed ketone formation. For the second monomer, a bis-Curtius rearrangement, in the presence of tert-butyl alcohol, converted both carbonyl moieties to BOC protected amines.