In Silico Discovery of Multistep Chemistry Initiated by a Conical Intersection: The Challenging Case of Donor–Acceptor Stenhouse Adducts

Detailed mechanistic understanding
of multistep chemical reactions
triggered by internal conversion via a conical intersection is a challenging
task that emphasizes limitations in theoretical and experimental techniques.
We present a discovery-based, hypothesis-free computational approach
based on first-principles molecular dynamics to discover and refine
the switching mechanism of donor–acceptor Stenhouse adducts
(DASAs). We simulate the photochemical experiment in silico, following the “hot” ground state dynamics for 10
ps after photoexcitation. Using state-of-the-art graphical processing
units-enabled electronic structure calculations we performed in total
∼2 ns of nonadiabatic ab initio molecular
dynamics discovering (a) critical intermediates that are involved
in the open-to-closed transformation, (b) several competing pathways
which lower the overall switching yield, and (c) key elements for
future design strategies. Our dynamics describe the natural evolution
of both the nuclear and electronic degrees of freedom that govern
the interconversion between DASA ground-state intermediates, exposing
significant elements for future design strategies of molecular switches.