Dynamic simulations of stimuli-responsive switching of azobenzene derivatives in self-assembled monolayers: reactive rotation potential and switching functions

Abstract

Although the force field (FF)-based molecular dynamics (MD) simulation has been widely applied to rationalise the experimental observations and measurements in chemistry, physics, materials and life science for years, traditional FF suffers from the incapability for describing chemical reactions, which are crucial in many important transformation processes. In order to simulate the collective switching process in azobenzene-based self-assemble monolayers on Au (111) surface, reactive MD simulations with alternative FF were implemented. The classic torsion function has been modified to depict the diabatic potential energy curves for cis and trans isomers, respectively. A switching function is further introduced to connect two NvN rotation functions, and the surface hopping between the cis and trans curves is allowed. By using the reactive rotation potential and switching function, the collective effect of numerous reaction centres and the influence of environment on the quantum yield in the complex system were explored at mesoscopic dimension and timescales. The reactive FF may be also applicable for other complicated systems containing stilbene derivatives. Limitation and perspective for further developments for the other complicated reactions are also addressed.

Do Columns of Azobenzene Stars Disassemble under Light Illumination?

“…46 In PCFF the potential energy is composed of bonded terms such as pairwise bonds, angles, torsions, Wilson out-of-plane angle coordinates, and cross-coupling terms, as well as nonbonded terms, which consist of the 9−6 Lennard-Jones (LJ) potential for the van der Waals interactions and of the electrostatic (Coulombic) interactions. This force field has been thoroughly tested and used extensively on azobenzene-containing systems such as azobenzene complexes, 47 azobenzene monolayers, 48,49 azobenzene chromophores in solutions, 50 azobenzene polymers, 51 and polymer networks. 52 In addition to the tabulated parameters of PCFF, a small number of parameters related to the azobenzene and dimethylamino groups have been supplemented from additional sources.…”

“…We therefore use a force field description of the azo-containing molecules and their isomerization behavior, which is compatible with established equilibrium force fields. Several approaches to implement the photoisomerization process of azobenzene in MD simulations that meet those requirements have been reported in the literature. − ,− …”

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars

“…Thus, switching between the trans and cis geometry of azobenzene can be incorporated. Out of multiple reported MD implementations of the photoisomerization reaction [39,42,43,[66][67][68][69][70][71][72][73], we employ the model of Heinz et al [42]. It has been used in various other simulation works [39,42,[73][74][75][76][77] and is consistent with the most important features of the isomerization of azobenzene.…”

Electrically Responsive Surfaces: Experimental and Theoretical Investigations

“…In those multiresponsive SAMs, theoretical models need some modifications, because those complex systems may consist of thousands of atoms and the switching is triggered by quantum-mechanical events under stimuli. A reactive molecular dynamics (RMD) method is well suited to deal with the light-driven switching of azobenzene-based SAMs, where the reactive potential energy curve for conformational transition, such as cis/trans conversion, is fitted from electronic structure calculations. − The MD simulations were also carried out on the novel pH/voltage/photoresponsive SAMs, whose functions depend on the formation of multiple salt bridges and guest release upon protonolysis modulated by the surface potential …”

“…We describe how surface sensitive vibrational sum-frequency generation (SFG) spectroscopy can be used to gain insights into the mechanistic principles underpinning electrically driven surfaces . It follows by outlining how molecular dynamics (MD) simulations can most successfully be applied to elucidate dynamic molecular-level events occurring on the surface in response to stimuli, being it an electrical stimulus , or other stimulus such as light − and pH …”