Supramolecular main chain liquid crystalline polymers utilizing azopyridine derivatives

Abstract

A series of main chain liquid crystalline polymers were formed through intermolecular hydrogen bonding between a functionalized bisazopyridine phenol and aromatic bisacids. The behaviour of these complexes was studied through differential scanning calorimetry and thermal polarizing optical microscopy. The presence of the hydrogen bonds was confirmed through infrared spectroscopy. These complexes formed thermotropic mesophases. The phases were determined to be nematic in nature from the schlieren textures of the optical micrographs. As the length of flexible spacer groups separating the mesogenic portions increased, the clearing temperatures of the mesophases decreased. As the length of the rigid component increased, the clearing temperature increased. A new bisacid species based on 2-hydroxy-6-naphthoic acid was used to increase clearing temperatures while remaining within an acceptable temperature window.

Recent Progress in Azopyridine-Containing Supramolecular Assembly: From Photoresponsive Liquid Crystals to Light-Driven Devices

“…During the slow evaporation of the mixed solution of 4-butoxybenzoic acid and one foursubstituent pyridine derivative, a new and extended mesogen was unexpectedly obtained through intermolecular H-bonding, with the molecular geometry directed along the long axis of the individual rod-like molecules. Other AzPy-carboxylic acid liquid-crystalline systems with small molecules were subsequently reported [30][31][32][33]. For example, Song and co-workers obtained a supramolecular liquid-crystalline complex from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid, where none of the pyridine-based derivatives were mesomorphic, but the H-bonded complexes were [34].…”

Azopyridine: a smart photo- and chemo-responsive substituent for polymers and supramolecular assemblies

“…Carboxylic acid/AzPy liquid crystal systems are superior to their azobenzene analogues as fast responsive dopants of liquid crystals. 26,27,55,56 Unlike liquid crystals doped with azobenzene-derived mesogens, which bend on the macroscopic scale and keep their shape in the dark, [57][58][59] heteroaryl azo chromophores such as AzPy can control the shape of films of a liquid crystal mesophase. This effect was demonstrated a few years ago in the case of a photoactive liquid crystalline polymer film doped with an azopyridine derivative.…”

Photochromic supramolecular azopolyimides based on hydrogen bonds

“…The drawback of these systems is the fact that for each combination of a polymer and an active molecule an organic synthesis is required which makes the sample preparation slower and more expensive. Alternative and thus the another way of preparation of azobenzene-containing polymers is the utilization of different nonconvalent intermolecular interactions hydrogen bond [5,27,[39][40][41][42][43][44][45][46][47]. Such approach offers a new convenient way to link the active molecules to the polymer chains thereby problems with often complicated synthetic routes for the preparation of the polymers with covalently bonded chromophores are eliminated.…”