Structure and photochemistry of fluorescent modified nucleobase

• Ano de defesa: 2024
• Autor(a) principal: Oliveira, Leonardo Miguel Farias de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Efeitos de solventes; Fotoquímica e fotofísica; Mecanismos de Relaxamento; Métodos multiconfiguracionais; Modified nucleobases; Multiconfigurational methods; Nucleobases modificadas; Photochemistry and photophysics; Relaxation Mechanisms; Solvent effects
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/46/46136/tde-15052025-121207/

In this thesis, we investigated the photochemistry of modified adenine nucleobases using multiconfigurational quantum chemistry methods. We focused on understanding how structural modifications influence the behavior of excited states in both gas phase and water. A static approach is employed to explore the relaxation pathways of excited states, while sequential quantum mechanics/molecular mechanics (s-QM/MM) is used to account for solvent effects. We employed methods such as CASSCF and MS-CASPT2 to accurately describe the electronic structures and potential energy surfaces (PESs) of two modified adenines: 26DAP (2,6-diaminopurine) and 8AZADAP (2,6-diamino-8-azapurine). We explored the photochemical relaxation pathways in detail, including fluorescence, conical intersections, and intersystem crossings. The results highlight the significant impact of structural modifications on the properties of excited states, which we correlated with experimental lifetime measurements. We found that modifications leading to higher energy barriers to crossing points, such as conical intersections, are associated with longer fluorescence lifetimes. Additionally, we explore the effects of tautomerism and solvent interactions on the photochemistry of 8AZADAP. This research offers valuable insights into the photoinduced mechanisms of modified nucleobases. By demonstrating how structural modifications affect the potential energy surfaces of excited states, we provide a detailed understanding of the photochemical events in these molecules. Additionally, we show that replacing a carbon atom with nitrogen in 8AZADAP enhances light emission.