Photochromic
materials are constructed with molecules accompanied
by structural change after triggering by light, which are of great
importance and necessity for various applications. However, because
of space-confinement effects, molecule stacking of these photoresponsive
chromophores within coordination polymers (CPs) always results in
an efficiency decrement and a response delay, and this phenomenon
will lead to a poor photochromic property. Herein, a CP (named CIT-E)
with a 3-fold-interpenetrating network structure, which was prepared
with (Z)-1,2-diphenyl-1,2-bis[4-(pyridin-3-ylmethoxy)phenyl]ethene
(1Z) and a CuI cluster, showed fast reversible photochromic
behavior. Under UV-light illumination, the color of CIT-Z changed
from pale yellow to reddish brown. With the illumination of green
light, the polymer could return to its initial color within 10 s.
To reveal the mechanism of reversible photochromic behavior of CIT-Z,
single-crystal structures of each color state were fully studied,
and other scientific study methods were also used, such as time-dependent
density functional theory calculation and control experiments. It
was found that, with light illumination, this behavior of CIT-Z was
the result of a ligand-to-metal charge-transfer process, and this
process was triggered by subtle molecular conformation variation of
tetraphenylethylene. It should be noted that CIT-Z has high thermal
and chemical stability, which are excellent advantages as smart photoresponsive
materials. As a proof of concept, a uniform thin film with such a
fascinating photochromic property allows applications in invisible
anticounterfeiting and dynamic optical data storage. Overall, the
present study opens up a new avenue toward reversible photochromic
materials.
Constructing varied dimensional coordination polymers (CPs) from the same chemical components is interesting but rare, which holds back to building the relationship between spatial topological structures and properties. Designing ligands with unequal coordination sites is a possible strategy to construct CPs with distinct spatial topologies. Herein, a novel planar ligand 2,7‐di(pyridin‐4‐yl)acridine (DPA) with two kinds of coordination N sites is prepared for coordinating with copper(I) iodide (CuI). 1D‐, 2D‐, and 3D‐CPs (named α‐, β‐, and γ‐CuI–DPA, respectively) are constructed by similar [Cu2I2] dimers and DPA building blocks but different CuI‐to‐DPA ratios. Interconversions among three CPs are verified. According to property characterization and structural analysis, 3D γ‐CuI–DPA with unique chains possesses charge movement pathways for higher electrical conductivity than those of the others. In addition, π–π stacking interactions are observed to play a significant role in promoting nonradiative migration and triggering photothermal conversion. This work presents a set of objects for investigating the structure‐to‐property connection of CPs in conductivity and photothermal conversion, as well as a roadmap for designing potential functional CPs materials in future.
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