Photoswitchable Fluorescent Crystals Obtained by the Photoreversible Coassembly of a Nucleobase and an Azobenzene Intercalator

Self-assembled nucleobases,
such as G-quartets or quadruplexes,
have numerous applications, but light-responsive structures are limited
to small, noncrystalline motifs. In addition, the assembly of the
widely exploited azobenzene photochromic compounds can produce fluorescent
crystals of extended dimensions but at the prize of sacrificing their
photoswitchability. Here, we overcome inherent limitations of self-assembly
with a new concept of supramolecular coassembly leading to materials
with unprecedented properties. We show that the coassembly of guanosine
monophosphate (GMP) with an azobenzene-containing DNA intercalator
produces supramolecular crystals arranged through a combination of
π–π, electrostatic, and hydrogen-bond interactions.
The resulting crystals are 100 μm long, pH-sensitive, fluorescent,
and can be photoreversibly disassembled/reassembled upon UV/blue irradiation.
This allows us to perform operations such as dynamic photocontrol
of a single-crystal growth, light-gated permeability in membrane-like
materials, and photoswitchable fluorescence. We believe this concept
critically expands the breadth of multifunctional materials attainable
by self-assembly.