Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations
Groenhof, Gerrit; Climent, Clàudia; Feist, Johannes; Morozov, Dmitry; Toppari, J. Jussi (2019). Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations. Journal of Physical Chemistry Letters, 10 (18), 5476-5483. DOI: 10.1021/acs.jpclett.9b02192
Published inJournal of Physical Chemistry Letters
© 2019 American Chemical Society
When photoactive molecules interact strongly with confined light modes in optical cavities, new hybrid light-matter states form. They are known as polaritons and correspond to coherent superpositions of excitations of the molecules and of the cavity photon. The polariton energies and thus potential energy surfaces are changed with respect to the bare molecules, such that polariton formation is considered a promising paradigm for controlling photochemical reactions. To effectively manipulate photochemistry with confined light, the molecules need to remain in the polaritonic state long enough for the reaction on the modified potential energy surface to take place. To understand what determines this lifetime, we have performed atomistic molecular dynamics simulations of room-temperature ensembles of rhodamine chromophores strongly coupled to a single confined light mode with a 15 fs lifetime. We investigated three popular experimental scenarios and followed the relaxation after optically pumping (i) the lower polariton, (ii) the upper polariton or (iii) uncoupled molecular states. The results of the simulations suggest that the lifetime of the optically accessibe lower and upper polaritons are limited by (i) ultra-fast photo-emission due to the low cavity lifetime and (ii) reversible population transfer into the 'dark' state manifold. Dark states are superpositions of molecular excitations but with much smaller contributions from the cavity photon, decreasing their emission rates and hence increasing their lifetimes. We find that population transfer between polaritonic modes and dark states is determined by the overlap between the polaritonic and molecular absorption spectra. Importantly, excitation can also be transferred "upwards" from the lower polariton into the dark-state reservoir due to the broad absorption spectra of the chromophores, contrary to the common conception of these processes as a "one-way" relaxation from the dark states down to the lower polariton. Our results thus suggest that polaritonic chemistry relying on modified dynamics taking place within the lower polariton manifold requires cavities with sufficiently long lifetimes and, at the same time, strong light-matter coupling strengths to prevent the back-transfer of excitation into the dark states. ...
PublisherAmerican Chemical Society
Publication in research information system
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Related funder(s)Academy of Finland
Funding program(s)Academy Project, AoF
Additional information about fundingThis work was supported by the Academy of Finland (Grants 289947 to JJT; 290677 and to GG) as well as the European Research Council (ERC-2016-StG-714870 to JF) and the Spanish Ministry for Science, Innovation, and Universities - AEI (RTI2018-099737-B-I00 to JF).
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