  We analyze how the photorelaxation dynamics of a molecule can be controlled
by modifying its electromagnetic environment using a nanocavity mode. In
particular, we consider the photorelaxation of the RNA nucleobase uracil, which
is the natural mechanism to prevent photodamage. In our theoretical work, we
identify the operative conditions in which strong coupling with the cavity mode
can open an efficient photoprotective channel, resulting in a relaxation
dynamics twice as fast than the natural one. We rely on a state-of-the-art
chemically-detailed molecular model and a non-Hermitian Hamiltonian propagation
approach to perform full-quantum simulations of the system dissipative
dynamics. By focusing on the photon decay, our analysis unveils the active role
played by cavity-induced dissipative processes in modifying chemical reaction
rates, in the context of molecular polaritonics. Remarkably, we find that the
photorelaxation efficiency is maximized when an optimal trade-off between
light-matter coupling strength and photon decay rate is satisfied. This result
is in contrast with the common intuition that increasing the quality factor of
nanocavities and plasmonic devices improves their performance. Finally, we use
a detailed model of a metal nanoparticle to show that the speedup of the uracil
relaxation could be observed via coupling with a nanosphere pseudomode, without
requiring the implementation of complex nanophotonic structures.
