Carmelo Naim
Laboratoire CEISAM, Nantes
Electronic spectroscopy is widely used across chemistry, materials science, and biology to probe the structure and dynamics of molecular systems. Computational modeling plays a central role in the interpretation of these experiments. Standard approaches are typically based on the calculation of excitation energies and vertical properties, such as oscillator strengths, evaluated at the Franck–Condon geometry. Although highly valuable, these approaches are often insufficient to achieve a quantitative reproduction of experimental observables [1]. In particular, the accurate prediction of spectral shapes and positions, as well as radiative and nonradiative rates, requires theoretical models that explicitly account for the coupling between electronic and nuclear motion, as well with explicit solvent effects.
A fully quantum treatment provides a rigorous description of the coupled electronic and nuclear dynamics. However, the computational cost of such approaches often limits their routine applicability. A widely used alternative is therefore to focus on the relevant regions of the potential energy surfaces and approximate them locally within the harmonic framework, while explicitly accounting for electronic–nuclear coupling (vibronic effects). This provides an efficient and robust description for semi-rigid systems and has proven successful for the description of a broad range of spectroscopies and excited-state decay processes [2]. Its practical implementation, however, depends on several choices, including the underlying electronic structure method, the vibronic model and the treatment of coupling terms.
In this seminar, I will discuss the main capabilities and limitations of harmonic vibronic approaches in standard applications, and I will highlight recent advances from my work on complex spectroscopic phenomena, including two-photon absorption, chiroptical properties, and decay rates in novel radicals materials for OLED applications [3].
Finally, I will discuss emerging applications of these approaches to rationalize the photophysics of high-spin systems (S > 1). Of particular interest will be radical–chromophore systems, where the radical character can be exploited to promote triplet-state generation and give rise to unconventional photophysical pathways [4]. Multiscale computational strategies will also be presented to incorporate environmental effects and assess how the surrounding medium influences the photophysical behavior of these challenging materials.
Bibliography
[1] Santoro, F. and Jacquemin, D. , WIREs Comput Mol Sci, 2016, 6, 460-486.
[2] Cerezo, J. and Santoro, J. Chem. Phys. 2023, 44, 626–643.
[3] Sarkar, R. et al., J. Chem. Theory Comput. 2025, 21, 3587–3599; Naim, C. and Jacquemin, Phys. Chem. Chem. Phys. 2025, 27, 19970–19986; Naim et al., Phys. Chem. Chem. Phys. 2025.
[4] O’Shea, J. M. et al., J. Am. Chem. Soc, 147, 1, 1017–1027 (2025)