posted on 2023-11-04, 13:20authored byTristan
H. Borchers, Filip Topić, Mihails Arhangelskis, Jogirdas Vainauskas, Hatem M. Titi, Oleksandr S. Bushuyev, Christopher J. Barrett, Tomislav Friščić
Cocrystallization of a cis-azobenzene
dye with
volatile molecules, such as pyrazine and dioxane, leads to materials
that exhibit at least three different light-intensity-dependent responses
upon irradiation with low-power visible light. The halogen-bond-driven
assembly of the dye cis-(p-iodoperfluorophenyl)azobenzene
with volatile halogen bond acceptors produces cocrystals whose light-induced
behavior varies significantly depending on the intensity of the light
applied. Low-intensity (<1 mW·cm–2) light
irradiation leads to a color change associated with low levels of cis → trans isomerization. Irradiation
at higher intensities (150 mW·mm–2) produces
photomechanical bending, caused by more extensive isomerization of
the dye. At still higher irradiation intensities (2.25 W·mm–2) the cocrystals undergo cold photocarving; i.e.,
they can be cut and written on with micrometer precision using laser
light without a major thermal effect. Real-time Raman spectroscopy
shows that this novel photochemical behavior differs from what would
be expected from thermal energy input alone. Overall, this work introduces
a rational blueprint, based on supramolecular chemistry in the solid
state, for new types of crystalline light-responsive materials, which
not only respond to being exposed to light but also change their response
based on the light intensity.