Preprint Article Version 1 This version is not peer-reviewed

Stacks of Azobenzene Stars: Self-Assembly Scenario and Stabilising Forces Quantified in Computer Modelling

Version 1 : Received: 12 November 2019 / Approved: 13 November 2019 / Online: 13 November 2019 (03:34:24 CET)

A peer-reviewed article of this Preprint also exists.

Savchenko, V.; Koch, M.; Pavlov, A.S.; Saphiannikova, M.; Guskova, O. Stacks of Azobenzene Stars: Self-Assembly Scenario and Stabilising Forces Quantified in Computer Modelling. Molecules 2019, 24, 4387. Savchenko, V.; Koch, M.; Pavlov, A.S.; Saphiannikova, M.; Guskova, O. Stacks of Azobenzene Stars: Self-Assembly Scenario and Stabilising Forces Quantified in Computer Modelling. Molecules 2019, 24, 4387.

Journal reference: Molecules 2019, 24, 4387
DOI: 10.3390/molecules24234387

Abstract

In this paper, the columnar supramolecular aggregates of photosensitive star-shaped azobenzenes with benzene-1,3,5-tricarboxamide core and azobenzene arms are analysed theoretically applying a combination of computer simulation techniques. Without a light stimulus, the trans-stars build one-dimensional columns of stacked molecules during the first stage of the noncovalent association. These columnar aggregates represent the structural elements of more complex experimentally observed morphologies -- fibers, spheres, gels and others. Upon UV light exposure, the azobenzene arms isomerise from thermodynamically stable planar trans- to a metastable kinked cis-state influencing the aggregate morphology. Here, we determine the most favourable mutual orientations of the \textit{trans}-stars in the stack in terms of (i) the pi-pi distance between the cores lengthwise the aggregate, (ii) the star slipped displacements and (iii) the rotation promoting the helical twist and chirality of the aggregate by calculating the binding energy diagrams using density functional theory. The model predictions are further compared with available experimental data. The intermolecular forces responsible for the stability of the stacks made of trans-azobenzene stars in crystals are quantified using Hirshfeld surface analysis. Finally, to characterize the self-assembly mechanism of such stars in solution, we calculate the hydrogen bond lengths, the normalized dipole moment and the binding energies as the functions of the columnar length using molecular dynamics trajectories, and conclude about the cooperative nature of this process.

Subject Areas

azobenzenes; self-assembly; cooperativity; hydrogen bonding; computer simulations

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