SUBSTITUENT EFFECTS ON THE ELECTRICAL-CONDUCTIVITY AND ELECTROCHEMICAL PROPERTIES OF CONJUGATED FURANYL PHENYLENE POLYMERS

A series of 1,4-bis(2-furanyl)benzenes, substituted at the 2 and 5 positions of the benzene ring with methyl, methoxy, and heptoxy groups, has been synthesized and electropolymerized. Spin density calculations of monomer radical cations show relatively high spin densities on the external alpha positions of the furan rings. These polymers exhibit conductivities of 10(-1)-10(0) S/cm when electrochemically oxidized in the presence of ClO4-. Cyclic voltammetry of the polymers has revealed redox states with E1/2 potentials ranging from 0.43 to 0.56 V vs Ag/Ag+ (+0.34 V vs SCE) which are dependent on the nature of the substituent. These potentials are not substantially affected by the length of the alkoxy chain. The onset of the pi to pi* transition, commonly termed the band gap, of the polymers ranges from 2.3 to 2.5 eV as determined using optoelectrochemical techniques and follows a similar trend. Redox thermodynamic studies, using Nernst plots of each system determined from an optical absorption technique, yield standard electrode potentials that decrease with the donating ability of the substituent. Electrogravimetric studies using a quartz crystal microbalance have demonstrated that the longer chain alkoxy-substituted polymers have a larger amount of mass increase associated with electrochemical oxidation. The doping levels, calculated from mass-transfer and charge-transfer results, increase as the length of the pendant substituent is increased.