Synthetic routes to soluble planar poly(phenylenethiophene)s and polythiophenes are described. The main polymer backbones are synthesized via Pd(0)-catalyzed couplings of the electron-rich N,N'-(bis-tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-n-butylstannyl)thiophene with electron-deficient aryldibromodiones. The prebridged polymers have bathochromically shifted absorptions due to donor/acceptor interactions between the consecutive repeat units. Upon exposure of the polymers to trifluoroacetic acid or titanium tetrachloride, imine bridges are formed that force the consecutive units into planarity. The bridging units are sp(2)-hybridized, thus allowing for greater electron delocalization between the consecutive aryl units. The syntheses of model trimeric systems were conducted to provide further data for assessing the optical properties of the polymers. Protonation of the imine moieties causes bathochromic shifts of >100 nm in several cases. The effect is explained by an intramolecular charge transfer. Thus these arrangements of planar structures with imine bridges serve as optically based proton sensors with spectral shift differences far-exceeding those of nonplanar imine-containing polymers.