Design of narrow-bandgap polymers. Syntheses and properties of monomers and polymers containing aromatic-donor and o-quinoid-acceptor units

A series of novel monomers and polymers containing aromatic-donor and o-quinoid-acceptor units was prepared, and the relationship between their spectral and electrochemical properties and their structures was investigated. X-ray structure analyses of the monomers possessing thiophene units revealed coplanar conformations, whereas calculations of the monomers containing N-methylpyrrole showed torsional conformations. Cyclic voltammetry showed amphoteric properties for all the monomers and p- and n-doping processes for most of the polymers. The reduction potentials were primarily dependent on the electron-accepting character of the o-quinoid-acceptor units. The electrochemical behavior of the polymers was characterized by cyclic voltammetry and suggested narrow-bandgap systems. The bandgaps determined from optical absorption spectra range from 0.5 to 1.4 eV. The polymer composed of thiophenes and benzo[1,2-c;3,4-c']bis[1,2,5]thiadiazole exhibited the narrowest bandgap.