| Summary: | Computational molecular spectroscopy, as a sub-field of quantum chemistry, allows one to obtain a comprehensive picture of investigated molecules and systems in terms of their structure and properties. It not only helps in the interpretation and understanding of the experimental spectra or predicting spectroscopic properties of molecular systems but can also be a great tool in the development of new materials. Various theoretical and computational methods have been successfully applied to solve different problems in many branches of science, however applying them to the investigation of larger and more complex systems remains a challenge. This work focuses on using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) methods to investigate the quantum chemical and spectroscopic properties of larger-sized systems. Four different types of molecules were studied, quantum dot (QD) clusters, endohedral fullerenes with an encapsulated metal atom, endohedral fullerenes with diatomic molecules, and the secondary structures of proteins. Methods to accurately and efficiently simulate X-ray and UV-Vis spectroscopy to reproduce experimental data and provide insights into the underlying chemical and physical processes associated with these techniques and the systems studied are provided.
Using quantum chemical calculations, it has been possible to gain more understanding of the photophysical process underpinning the operation of QD-based fluorescent probes, and to support the design of QD-based optical sensors for the detection of biomolecules. Theoretical methods have been also successfully applied to achieve a better picture of super atomic molecular orbitals (SAMOs) within the endohedral fullerenes and to provide insights into the potential for design of novel advanced materials for molecular electronics. The non-resonant X-ray emission spectroscopy of amino acids and a dipeptide have been studied using TDDFT calculations at the nitrogen and oxygen Kedges. Calculations for the model α-helix and β-sheet structures showed the spectra to be relatively insensitive to the structure of peptide bond, with the greatest variation observed at the oxygen K-edge. Combining TDDFT with Franck–Condon simulations has allowed to simulate vibrationally resolved X-ray absorption spectra of nitrogen encapsulated within C60 (N2@C60). The studies have showed sensitivity of the spectra and spectroscopic properties of N2 to the presence of the C60 cage.
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