Irreversible Organic Crystalline Chemistry Monitored in Real Time
Peter R. Poulin and
Keith A. Nelson*
Because multiple laser shots are typically required to monitor
ultrafast photochemical reaction dynamics, sample depletion
and product accumulation have greatly restricted the range of
substrates and structural environments amenable to study. By
implementing a two-dimensional spatial delay gradient across
the profile of a femtosecond probe pulse, we can monitor in
a single laser shot organic crystalline reaction dynamics despite
the formation of permanent photoproducts that cannot be conveniently
removed. We monitored the photolysis of the triiodide anion,
I
3–, and subsequent recombination or relaxation of its
reaction products, in three very different pure organic molecular
crystals. The experimental results and associated molecular
dynamics simulations illustrate the intimate connection between
lattice structure and reaction dynamics, highlighting the role
of lattice constraints in directing phase-coherent geminate
recombination of photofragments within a crystalline reaction
cage.
* To whom correspondence should be addressed. E-mail: kanelson{at}mit.edu
