Preferential Face-on and Edge-on Orientation of Thiophene Oligomers by Rational Molecular Design.

Precise control over the supramolecular organization of organic semiconducting materials guiding to exclusive face-on or edge-on orientation is a challenging task. In the present work, we study the preferential packing of thiophene oligomers induced through rational molecular designing and self-assembly. The acceptor-donor-acceptor type oligomers having 2-(1,1-dicyano-methylene)rhodanine as acceptor (OT1) favored a face-on packing, while that of functionalized with N-octyl rhodanine (OT2) preferred an edge-on packing as evident from 2D-grazing incidence angle X-ray diffraction, tapping-mode atomic force microscopy (AFM) and Raman spectroscopy analyses. As an outcome of the preferred orientation, the oligomers exhibited anisotropic conductivity in the self-assembled state, revealed by the conducting AFM experiment.