Butterfly-Shaped Thiophene-Pyridine Hybrids: Green Electroluminescence and Large Third-Order Optical Nonlinearities.

A set of four symmetric, butterfly-shaped 4-(4-(decyloxy)phenyl)-2,6-di(thiophen-2-yl)pyridine (TPY) derivatives 2TPA-TPY (TPY center and triphenylamine end groups), 2CBZ-TPY (TPY center and N-ethyl carbazole end groups), 2TPY-TPA (triphenylamine center and TPY at the periphery) and 2TPY-CBZ (N-ethyl carbazole center and TPY at the periphery) was synthesized. The molecules show reverse saturable absorption (RSA) which is consistent with two-photon absorption (2PA) associated with excited-state absorption (ESA) when excited using a 532 nm laser beam. The molecules 2TPA-TPY and 2TPY-TPA possess extremely low limiting thresholds of 1.73 and 2.68 J cm-2 , respectively. An organic light-emitting diode (OLED) fabricated from 2TPA-TPY exhibits green emission with a maximum luminance of 207 cd m-2 , a current efficiency (ηCE ) of 1.51cd A-1 , a maximum power efficiency (ηPmax ) of 0.46 lm W-1 and an external quantum efficiency (ηEQE ) of 0.48 % at 100 cd m-2 .

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, whereas 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. The oligomers exhibited anisotropic conductivity in the self-assembled state as an outcome of the preferred orientation, revealed by the conducting AFM experiment.