Computational Investigation of Excited-State Dynamics in Charge-Donor-Acceptor SERS Systems Using Multiconfigurational Methods

• Grant number: 25/20806-7
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: January 01, 2026
• End date: August 31, 2030
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Rômulo Augusto Ando
• Grantee: Pedro Meireles Freire
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 22/11983-4 - Spectroscopy signal enhancement: nanomaterials, theory, and computer simulation, AP.TEM

Abstract

The description of excited states constitutes one of the main challenges in theoretical chemistry, as their multireference nature requires the use of multiconfigurational (MC) methods for accurate characterization. These states, arising from electronic transitions induced by electromagnetic radiation, are at the core of relevant chemical phenomena such as luminescence, photochemical reactions, and spectroscopies including resonance Raman and surface-enhanced Raman scattering (SERS). The SERS effect, resulting from the interaction between molecules and metallic nanoparticles, involves the amplification of the Raman signal through the resonance between surface plasmons and the incident radiation. However, the observed enhancement patterns are difficult to rationalize, since the molecule-metal interaction alters the electronic structure and may generate excited states, particularly metal-molecule charge-transfer states, that contribute to the resonance Raman effect. In this context, MC methods and multilevel (QM/QM) approaches offer a promising route to understand the so-called Chemical Effect (CE) associated with adsorption, resonance, and charge transfer in SERS spectra. This project proposes a systematic study of these excited states, modeling different electronic transitions in order to elucidate the role of CE in the selective enhancement of vibrational modes and to deepen the understanding of the fundamental mechanisms of surface-enhanced Raman spectroscopy. (AU)