Anion−π Interaction-Directed Assembly of Polyoxometalate-Based Host–Guest Compounds and Its Contribution to Photochromism

Two rare copper-based host–guest
crystalline compounds were
synthesized with different photoresponsive reversible visible light
photochromism as a result of blending of distinctively different functional
components, naphthalenediimides (NDIs) tectons and polyoxometalates.
A slight adjustment of the substituent of the diimide nitrogens, from
rigid to semirigid ligands, will result in different modes of anion−π
interactions, which eventually lead to different structures and different
sensitivities to visible light. The unique anion−π interactions
impart significant impacts on the structures of the compounds and,
to some extent, the ability to gain or lose electrons of the NDIs
of the compounds, which is evident from subtle changes in photochromic
sensitivity and reduction potentials; if compounds bear more and stronger
anion−π interactions, this might dramatically enhance
the compounds’ stability and diminish the π-electron-deficient
property of the core naphthalene ring of the NDIs.