Computational investigations of mechanisms, pathway complexity and dipole dynamics in supramolecular polymers

Abstract

Supramolecular chemistry is coined as ’chemistry beyond a molecule’ as it is based on interactions between molecules, contrary to traditional chemistry focusing on the formation of covalent bonding within a molecule. [1] The term ’supramolecule’ was introduced by Karl Lothar Wolf et al. in 1937. [2] The interactions between the molecules are non-covalent and weak. They include dipole-dipole, [3–8] van der Waals, electrostatic, [9–11] - , [12] hydrogen bonding, [13] hydrophobic, [14–16] metal-ligand coordination, [17–19] charge-transfer, [20, 21] integrated non-covalent interactions such as host-guest interactions [22, 23] and so forth. Although these interactions are weak, their combined effect can produce structurally and chemically stable structures of various architectures such as spheres, rods, cylinders, sheets etc. [24– 26] Non-covalent interactions, such as hydrogen bonds are highly directional and reversible in nature. Thus, materials formed through these interactions retain their polymeric properties in solution. [27, 28] Owing to the directionality and reversibility of these secondary interactions, these polymers have good material properties with low viscosity, which makes them easily processible. Besides, they possess some fascinating functionalities such as recyclability, ability to self-heal, and can be stimuliresponsive. [29] The characterisation of the supramolecular polymers is a daunting task due to their dynamic nature and cannot be done using standard techniques used for conventional polymers. A combination of several techniques including size exclusion chromatography, light scattering techniques, viscometry, fluorescence, circular dichroism (CD), ultraviolet-visible (UV/Vis), mass spectrometry, NMR spectroscopy, scanning probe microscopy, vapour pressure osmometry and electron microscopy can characterise supramolecular polymerisation.