Tuning of the mesogenic, electronic, and optical properties of new conjugated 3,3 '-bipyridine derivatives

We present two series of new 6,6'-distyryl-3,3'-bipyridine derivatives synt hesized via a Knoevenagel condensation reaction of 6,6'-dimethyl-3,3'-bipyr idine in the first series, and 5,5',6,6'-tetramethyl-3,3'-bipyridine in the second one, with aromatic aldehydes para-substituted with electron donor o r acceptor groups. These molecules were characterized by spectroscopic meth ods (NMR, UV-vis, photoluminescence), and cyclic voltammetry. Some compound s were found to exhibit thermotropic liquid crystalline (LC) phases, whose structures were analyzed by DSC and optical microscopy. The effects of mole cular design on the mesogenic behavior, redox potentials, and fluorescence (nature and lifetimes of the excited states) were investigated. The high de gree of conjugation and the mesogenic character of these molecules can lead to nonlinear optical (NLO) applications for the "push-pull" compounds. Abs orption in the UV range and high fluorescence are other characteristics of some members of this group. The latter property, associated with high elect ron affinity, opens up light-emitting diode (LEDs) applications.