Steric Control of Conductivity in Highly Conjugated Polythiophenes

A series of 4-alkylidene-, 4-alkyl-, and 4,4‘-dialkyl-substituted 4H-[5,1-b;1,5-b‘]cyclopentabithiophenes was designed in which the substituents in position 4 occupy well-defined areas in the space around the bithiophene unit to evaluate the effects played by their steric properties on the electrical conductivity of the materials resulting from anodic polymerization. The geometry of all the monomers was either inferred from X-ray diffractometric analysis or calculated through molecular modeling techniques. The polymers were prepared under identical experimental conditions and characterized by CV, IR, and UV−vis spectroscopy and in situ conductivity. Various types of molecular descriptors were utilized to create QSPR models, which demonstrated a good relationship between the molecular structure of the monomers and the conductivity of the corresponding polymers.