Modeling Dark- and Light-Induced Crystal Structures and Single-Crystal Optical Absorption Spectra of Ruthenium-Based Complexes that Undergo SO2-Linkage Photoisomerization
A family of coordination complexes of the type [Ru(SO2)(NH3)4X]Y exhibit optical-switching capabilities in their single-crystal state. This striking effect is caused by photoisomerization of metastable photoinduced states, which are metastable if kept at suitably low temperatures. This illustrates the possibility of these materials to operate as nanotechnological devices themselves, with the potential for optical actuation, optical-signal processing and nano-optomechanical function. This thesis presents a Plane-Wave (PW) – Density Functional Theory (DFT) based periodic methodology that can effectively model the dark- and light-induced structures, and single-crystal optical absorption spectra of these complexes. Initially, these crystalline materials are modeled via PW-based periodic and Molecular Orbital (MO)-DFT based molecular fragment models, and time-dependent DFT (TDDFT), to calculate their structural and optical properties, which are compared with experimental data. Both the periodic and molecular fragment models simulate these complexes effectively, with small deviations in key bond lengths, successfully replicating experimentally-determined structures. Both models also simulate trends in experimentally-determined optical absorption spectra effectively, with optical absorbance and coverage of the visible region increasing with the formation of the photoinduced geometries. This represents the first study of the optical properties of materials from this family of complexes via DFT-based methods. The PW-DFT study is then expanded to consider more complexes, including both photoswitches and transducers. Periodic models are shown to appreciate the competing chemical and crystallographic forces present in these complexes, namely the possible effects of the trans-influence and intermolecular interactions on the simulated optical absorption spectra. Density of states calculations are also showed to appreciate these forces, whilst illustrating the potential for optical tuning capabilities. The periodic models are also used to conduct a study of the photoisomerization process from the dark to the light-induced structures via the Nudged Elastic Band (NEB) method; thereby a ‘cause-and-effect’ relationship between photoisomerization and transduction is suggested to be dependent heavily on the intermolecular forces present. Synthetic work has also been carried out in parallel, resulting in the development of a more sustainable precursor-synthesis route and the synthesis of two new complexes. This thesis demonstrates that PW-TDDFT should be considered as a more than viable method for simulating the optical and electronic properties of this family of single-crystal optical switches whose functionality is based on linkage photoisomerism. It also illustrates the potential for optically tuning these complexes so that they can be developed with desired properties for tailored applications
