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) (P PP) derivatives. The first approach, involving lactam bridges, was uns uccessful due to the insolubility of the 6(5H)-phenanthridinonyl moiet ies. The second approach, which utilized imine bridges, worked excelle ntly since the compounds were generally soluble and the bridge formati ons were highly efficient. The main PPP backbone was synthesized via P d(0)-catalyzed coupling of an arylbis(boronic ester) with an aryl dibr omide. Imine bridges, which are formed by exposure of the polymer to t rifluoroacetic acid or HCl, force the consecutive units into planarity . The bridging units are sp(2) hybridized, thus allowing for greater p i-electron flow between the consecutive phenyl units. The polymers, up on 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. Additiona lly, an improved method is described in which a common intermediate, a n 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 sel ective alkylation or arylation of the acyl portions was accomplished u sing lower order cyanocuprates or Pd(0)-catalyzed ketone formation. Fo r the second monomer, a bis-Curtius rearrangement, in the presence of tert-butyl alcohol, converted both carbonyl moieties to BOC protected amines.