Photoinduced processes of multichromophoric organic conjugated materials frequently involve concerted dynamics of coupled electronic and vibrational degrees of freedom (i.e. vibronic couplings) that can give rise to persisting phase relations or coherences. Fundamental insights into the coherence creation and destruction mechanisms can potentially allow the manipulation of photoexcited non-radiative pathways to achieve desired efficient transfer of energy and charges.

Direct quantum molecular simulations using the ab initio multiple cloning (AIMC) approach [1,2] is a controllable approximation to non-adiabatic dynamics and naturally includes electronic decoherence. Their modeling results can be used to predict nonlinear X-ray signals that track its coherent behavior.

Vibrational funnels may support persistent coherences. The ultimate confirmation of their role on the inter-chromophoric energy transfer can be achieved by performing nonadiabatic excited state molecular dynamics simulations by selectively freezing the nuclear motions in question[3]. This results a useful tool to identify and evaluate the impact of these vibrational funnels on the energy transfer processes and guide in silico design of materials with tunable properties and enhanced functionalities.

Herein, AIMC have been applied to analyze coherences during the inter-chromophore energy transfer of two different organic conjugated materials: (a) a rigid synthetic molecular heterodimer presenting persistent coherence[4,5]; (b) a flexible dendrimer whose initial ultrafast coherent dynamics is followed by incoherent mechanisms governed by thermal fluctuations that ultimately lead to a random molecular scrambling[6].

References
[1] “Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics” D. V. Makhov, W. J. Glover, T. J. Martinez and D. V. Shalashilin, J. Chem. Phys., 141, 054110 (2014).
[2] “An Ab Initio Multiple Cloning approach for the simulation of photoinduced dynamics in conjugated molecules” V. M. Freixas, S. Fernandez-Alberti*, D. V. Makhov, S. Tretiak, and D. Shalashilin, Phys. Chem. Chem. Phys. 20, 17762 - 17772 (2018).
[3] “Photoinduced dynamics with constrained vibrational motion: FrozeNM algorithm” H. Negrin-Yuvero, V. M. Freixas, B. Rodriguez-Hernandez, G. Rojas-Lorenzo, S. Tretiak, A. Bastida and S. Fernandez-Alberti, J. Chem. Theory Comput. 16, 12, 7289-7298 (2020).
[4] "Vibronic Quantum Beating between Electronic Excited States in a Heterodimer" V. M. Freixas, S. Tretiak, D. V. Makhov, D. Shalashilin, and S. Fernandez-Alberti, J. Phys. Chem. B, 124(19), 3992-4001 (2020).
[5] “Monitoring Molecular Vibronic Coherences in a Bichromophoric Molecule by Ultrafast X–Ray Spectroscopy” Daniel Keefer, Victor M. Freixas, Huajing Song, Sergei Tretiak , Sebastian Fernandez-Alberti and Shaul Mukamel, Chem. Sci,, 12, 5286-5294 (2021).
[6] “Ultrafast coherent photoexcited dynamics in a trimeric dendrimer probed by X-ray stimulated-Raman signals” Victor M. Freixas, Daniel Keefer, Sergei Tretiak, Sebastian Fernandez-Alberti, and Shaul Mukamel, Chem. Sci., 13, 6373-6384 (2022