Variable temperature studies on mesogenic polythiophenes using 2D-IR and WAXS

Abstract

We synthesized and investigated the molecular ordering of 4-{(E)-[(4-alkoxy phenyl imino] methyl} phenyl] thiophene-3-carboxylate (APTC) oligomers of varying alkoxy chain lengths using polarised Infrared spectroscopy (IR) and wide-angle X-ray scattering (WAXS). Infrared polarisation study shows maximum dichroic ratio for Phenyl CC stretching for Decyloxy (PDPTC) at room temperature. During heating C–O–C shows higher dichroic ratio in dodcecyloxy (PDDPTC) due to the restrains in the torsional angle and hindered rotation of it. By using temperature as perturbation, IR correlation (2D-IR) was performed. 2D-IR analysis results are classified into three parts. First, at phase temperature, CO splits into two peaks due to dipole–dipole interaction; second, chain bending in CH2 alkyl chain and variation in CH2 stretching with molecular environment and third, thiophene out of plane bending vibration shows main chain thiophene flipping with respect to alkoxy chain length. In addition to that, an intriguing evidence of liquid crystalline phase stability by CO dipole moment over alkyl chain is seen. 2D-IR analysis of thiophene region also shows “four-leaf clover pattern” on increasing alkoxy chain length and a change in phenyl group C–H in plane bending vibration along with it is evidenced. Hetero correlation between WAXS and IR shows interlayer packing variation with zigzag alignment for lower homologues and linear alignment for higher homologues with lower ‘d’ spacing value plotting with change in CH2 stretching vibration of alkoxy chain length.