2 research outputs found
Photochemistry and spectroscopy of molecules at surfaces: Insights from ab initio molecular dynamics
Resumen del trabajo presentado al 2nd CECAM Workshop: "Challenges in reaction dynamics of gas-surface interactions and methodological advances in dissipative and nonadiabatic processes", celebrado en Toulouse (France) del 27 al 30 de septiembre de 2021.Peer reviewe
The Photoinduced <i>E</i> → <i>Z</i> Isomerization of Bisazobenzenes: A Surface Hopping Molecular Dynamics Study
The photoinduced <i>E</i> → <i>Z</i> isomerization of azobenzene is a prototypical
example of molecular
switching. On the way toward rigid molecular rods such as those for
opto-mechanical applications, multiazobenzene structures have been
suggested in which several switching units are linked together within
the same molecule (Bléger et al., <i>J. Phys. Chem. B</i> <b>2011</b>, 115, 9930–9940). Large differences in
the switching efficiency of multiazobenzenes have been observed, depending
on whether the switching units are electronically decoupled or not.
In this paper we study, on a time-resolved molecular level, the E→
Z isomerization of the simplest multiazobenzene, bisazobenzene (BAB).
Two isomers (<i>ortho-</i> and <i>para-</i>BAB),
differing only in the connectivity of two azo groups on a shared phenyl
ring will be considered.To do so, nonadiabatic semiclassical dynamics
after photoexcitation of the isomers are studied by employing an “on-the-fly”,
fewest switches surface hopping approach. States and couplings are
calculated by Configuration Interaction (CI) based on a semiempirical
(AM1) Hamiltonian (Persico and co-workers, <i>Chem. Eur. J.</i> <b>2004</b>, 10, 2327–2341). In the case of <i>para-</i>BAB, computed quantum yields for photoswitching are
drastically reduced compared to pristine azobenzene, due to electronic
coupling of both switching units. A reason for this (apart from altered
absorption spectra and reduced photochromicity) is the drastically
reduced lifetimes of electronically excited states which are transiently
populated. In contrast for <i>meta-</i>connected species,
electronic subsystems are largely decoupled, and computed quantum
yields are slightly higher than that for pristine azobenzene because
of new isomerization channels. In this case we can also distinguish
between single- and double-switch events and we find a cooperative
effect: The isomerization of a single azo group is facilitated if
the other azo group is already in the <i>Z</i>-configuration