Ionic Hydrogen-Bonded Organic Frameworks with a Two-Photon Synergistic Color Change and Their Information Encryption Applications

Photochromic hydrogen-bonded organic
frameworks (HOFs)
can introduce
different luminescent functional groups to achieve synergistic controlled
multiple color change properties, which are in great demand for diverse
information encryption applications. We report in this paper switchable
photochromic and photoluminescent dual luminescent functional group
HOFs constructed with synergistic effects by N,N′-bis(2-phenylalanine)-1,4,5,8-naphthalenediimine
(H2PheNDI) and benzenecarboximidamide 4,4′-azobis(hydrochloride)
(AZBH). The crystal powder of iHOF-41 is orange–red
in color, which can be changed to black under the irradiation of a
365 nm ultraviolet (UV) light source for 15 min. The photoisomerization
rate of the crystal solution under continuous UV irradiation for 5
h was close to 99%. The composite membranes can achieve the properties
of photochromism and photoluminescence when they are discolored under
365 nm UV irradiation and, at the same time, excite red bright fluorescence.
This work achieves the construction of HOFs based on switching biluminescent
functional groups and explores the synergistic mechanism of the photoisomerization
process and photochromism as well as its practical application in
information encryption.