Methyl substituted, azine bridged poly thiophenes and their structure related surface characteristics

Abstract

Three semiconducting azine bridged thiophene based organic polymers have been synthesized and their surface conductivity has been evaluated as a function of the methyl group, both experimentally and theoretically. These semiconductive polymers, poly[(1,2-bis(thiophen-2-yl-methylene)hydrazine)], poly[(1,2-bis((3-methyl-thiophen-2-yl)methylene)hydrazine)] and poly[(1,2-bis(1-(thiophen-2-yl)ethylidene)hydrazine)] (abbreviated as PBTMH, PB3MTMH and PBTEH respectively) were prepared by chemical oxidative polymerization and characterized by NMR, UV–vis and IR spectroscopy. The molecular weight of the polymers was determined by Size exclusion chromatography (SEC). The surface conductivity and its isothermal stability were evaluated by Four-probe technique and the surface morphology was studied by SEM. Tafel polarization study revealed the exchange current density and cathodic characteristics of the polymers, and the theoretical calculation provided the pattern of electron delocalization in the polymers. Of the three polymers, PB3MTMH is found to have lower band gap, higher DC electrical conductivity and its isothermal stability, higher exchange current density than PBTMH and PBTEH. The characteristics of these polymers have been explained in terms of structure-activity correlation. The polymers have been evaluated to be semiconducting and the order of their electrical conductivity is PB3MTMH > PBTMH > PBTEH. This study demonstrates that the methyl substituent can suitably alter the conductivity of the polymer. The effect of substitution of the methyl (−CH3) group in various positions of azine bridged polythiophene revealed that the methyl substituted polymers showed improved conductivity and the one with methyl group substitution on thiophene ring showed higher electrical conductivity than the methyl group substitution on imine carbon. The synthesized polymers are reported for the first time and show higher electrical conductivity than already reported azine polymers.