Simulation Studies of Light-Induced Self-Assembly in Colloids

Photoresponsive ligands coated on nanoparticle-surfaces are often used to achieve Light-induced self-assembly (LISA), a technique useful to tuning material properties. For example, azobenzene dithiol (ADT), which is a photoresponsive ligand, can switch between trans-and-cis configurations on its exposure to ultraviolet light, allowing self-assembly in ADT-coated gold nanoparticles (NPs). This behavior is attributed to a higher dipole moment of cis-ADT over trans-ADT which leads to a dipole–dipole attraction facilitating self-assembly. More precisely, it is related to the interaction energy of a pair of ADT ligands in their cis and trans conformations when attached to NPs. We show that this interaction energy between ADT ligands can be quantified using quantum-chemistry calculations and the ligand–ligand interaction energy can be used to calculate the total effective interaction energy between a pair of cis as well as trans ADT-coated NPs. Using the effective interaction energy, we obtained a generalized potential energy function, which was applied in Langevin dynamics simulations to capture LISA in gold nanoparticles.