Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π–π Stacking Counterions

Abstract

Organic semiconductor materials composed of π–π stacking aromatic compounds have been under intense investigation for their potential uses in flexible electronics and other advanced technologies. Herein we report a new family of seven π–π stacking compounds of silver(I) bis-N-(4-pyridyl) benzamide with varying counterions, namely [Ag(NPBA)2]X, where NPBA is N-(4-pyridyl) benzamine, X = NO3− (1), ClO4− (2), CF3SO3− (3), PF6− (4), BF4− (5), CH3PhSO3− (6), and PhSO3− (7), which form extended π−π stacking networks in one-dimensional (1D), 2D and 3D directions in the crystalline solid-state via the phenyl moiety, with average inter-ring distances of 3.823 Å. Interestingly, the counterions that contain π–π stacking-capable groups, such as in 6 and 7, can induce the formation of mesomorphic phases at 130 °C in dimethylformamide (DMF), and can generate highly branched networks at the mesoscale. Atomic force microscopy studies showed that 2D interconnected fibers form right after nucleation, and they extend from ~30 nm in diameter grow to reach the micron scale, which suggests that it may be possible to stop the process in order to obtain nanofibers. Differential scanning calorimetry studies showed no remarkable thermal behavior in the complexes in the solid state, which suggests that the mesomorphic phases originate from the mechanisms that occur in the DMF solution at high temperatures. An all-electron level simulation of the band gaps using NRLMOL (Naval Research Laboratory Molecular Research Library) on the crystals gave 3.25 eV for (1), 3.68 eV for (2), 1.48 eV for (3), 5.08 eV for (4), 1.53 eV for (5), and 3.55 eV for (6). Mesomorphic behavior in materials containing π–π stacking aromatic interactions that also exhibit low-band gap properties may pave the way to a new generation of highly branched organic semiconductors.

Cyclotriphosphazenes as Scaffolds for the Synthesis of Metallomesogens

“…Although to far less an extent, isocyanides have been also described as versatile ligands for the preparation of mesogenic ionic Ag­(I) complexes either having calamitic or columnar mesomorphism depending on the number of peripheral aliphatic chains of the ligands . The mesomorphic arrangement of functional ligands connected with the particular properties introduced by silver atoms has recently been applied to the preparation of ion-conductive functional materials or organic semiconductors, among other applications . Nevertheless, the silver­(I) liquid crystalline complexes described so far have a conventional structure.…”

“…4 The mesomorphic arrangement of functional ligands connected with the particular properties introduced by silver atoms has recently been applied to the preparation of ion-conductive functional materials 5 or organic semiconductors, among other applications. 6 Nevertheless, the silver(I) liquid crystalline complexes described so far have a conventional structure. Cyclo-triphosphazenes provide new possibilities to the design of metallomesogens by using as a core with three nitrogen atoms able to coordinate metallic entities, e.g., silver(I) derivatives, and with additional substitution on the P atoms.…”