Regensburg 2025 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 13: Molecular Electronics and Excited State Properties I

CPP 13.1: Vortrag

Montag, 17. März 2025, 17:15–17:30, H38

Revealing the Origin of low-energy Excited State Absorption in the nonlinear Optical Properties of Thiophene — •Mustapha Driouech, Michele Guerrini, and Caterina Cocchi — Carl von Ossietzky Universität Oldenburg

Optical nonlinearities in organic molecules are useful for advanced applications. Among them, optical limiting is particularly relevant to prevent critical damage to the human eyes and artificial sensors from intense radiation. In this ab initio study, we investigate the nonlinear optical properties of thiophene oligomers with a non-perturbative approach based on real-time time dependent density functional theory [1]. We study the optical absorption spectra obtained after applying a broadband instantaneous electric field. For sufficiently high intensities, we observe the appearance of absorption peaks at low energies that are not present in the linear spectra. To investigate in more details the nonlinear mechanisms involved, we perform pump-probe simulations combined with analysis of the population dynamics revealing that the emerging features are due to excited state absorption in the visible region. Our results show that this fully ab initio methodology is able to capture and unravel the fundamental mechanisms of optical nonlinearities in organic molecules.
[1] C. Cocchi, et al., Phys. Rev. Lett. 112, 198303 (2014).

Keywords: Real-Time Time Dependent Density Functional Theory; Thiophene Oligomers; Transient Absorption Spectra; Nonlinear Optics