Molecular dynamics simulations of alkyl substituted nanographene crystals

Abstract

Discotic polyaromatic molecules, similar to nanometric graphene flakes, constitute an interesting class of materials for organic electronic applications. Grafting flexible side chains around the periphery of such molecules enhances their processability and gives rise to diverse behaviours, such as the manifestation of liquid-crystalline character and anisotropic mechanical response. In this work, we examine by means of molecular dynamics simulations the properties of molecular crystals comprised of alkyl-substituted hexa-peri-hexabenzocoronene mesogens. Pristine and mono-substituted systems by hydrogen or iodine atoms are modelled, with variable side chain length. A general structural and mechanical robustness to peripheral substitution is reported, with the mesogens forming tightly packed molecular wires even at elevated temperature and pressure. In their discotic ordering, the molecules present relatively low translational mobility, a beneficial phenomenon for charge transport. A thermotropic dependence of the mechanical response is identified, with the systems behaving differently in their room-temperature crystalline phase and in their liquid-crystalline phase at elevated temperatures. The melting process is also examined, elucidating an initial negative expansion along a high symmetry direction and the existence of a metastable state, before falling into the final liquid-crystalline state.

Identifying high-mobility tetracene derivatives using a non-adiabatic molecular dynamics approach

“…This type of FF has been successfully used in the literature for simulating a variety of functionalized PAH molecular crystals. [51][52][53] The accuracy of united-atom FF representations for aliphatic nanophases for molecular crystals made up by soluble molecules with core-shell morphologies has been thoroughly demonstrated in the literature, starting from the early studies of Maliniak 54 and Bast and Hentschke 55 and leading up to recent implementations for either structural and dynamical properties 51,56,57 and charge transfer properties. [58][59][60][61] Its suitability for MD simulations of tetracene derivatives is confirmed via validation of structural properties with respect to the available experimental information.…”

Computational Studies of Nanographene Systems: Extended Discotics, Covalently Linked “Supermolecules,” and Functionalized Supramolecular Assemblies

“…Appropriate force field terms missing from the aforementioned compilation are taken from the work of Marcon et al 38 The validity of the latter hybrid force field has already been tested for functionalized HBC systems in the literature. 36,38,39 Molecular Dynamics (MD) simulations are carried out in the isothermal-isostress statistical ensemble for bulk molecular crystals with three-dimensional periodicity and for isolated molecular wires with one-dimensional periodicity by means of the Martyna-Tobias-Klein equation of motion. 83 An integration step of 1fs is adopted and the thermostat and barostat damping constants are taken as 100 fs and 2500 fs respectively.…”

“…From a structural point of view, our building procedure for C12 systems reproduces the reported end-to-end distance of approximately 1.23 nm at room temperature. 88 Explicit hydrogen configurations are subsequently mapped onto a well-tested for discotic systems hybrid united-atom/all-atom representation 36,39 via the unification of aliphatic hydrogen atoms with their first neighboring sp 3 carbon atoms.…”

“…[15][16][17][18] Regarding theoretical work on nanographene materials, an abundance of studies across multiple simulation scales have been carried out in the literature, including ab initio and Density Functional Theory (DFT) analyses for structural and electronic properties [19][20][21][22][23][24][25][26][27][28][29] and charge transfer properties. [30][31][32][33] At the level of molecular wires and bulk molecular crystals, atomistic simulations [34][35][36][37][38][39] have elucidated phenomena of structural, mechanical, thermodynamic and dynamical nature. Furthermore, a plethora of multiscale studies [40][41][42][43][44][45][46] have contributed to the understanding of aspects regarding the charge transfer capabilities of discotic materials with respect to supramolecular structure and dynamics.…”

Molecular Simulations of Nanographene Systems

“…Mesh based techniques are employed in order to account for the periodic nature of long range interactions [14]. The quantification of particle interactions is accomplished through an empirical force field capable of capturing the properties of such materials [15].…”