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 pos itions of the benzene ring with methyl, methoxy, and heptoxy groups, h as 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 co nductivities of 10(-1)-10(0) S/cm when electrochemically oxidized in t he 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 substituen t. These potentials are not substantially affected by the length of th e 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. Red ox thermodynamic studies, using Nernst plots of each system determined from an optical absorption technique, yield standard electrode potent ials that decrease with the donating ability of the substituent. Elect rogravimetric studies using a quartz crystal microbalance have demonst rated 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 resu lts, increase as the length of the pendant substituent is increased.