Ionic\nHydrogen-Bonded\nOrganic Frameworks with a Two-Photon\nSynergistic Color Change and Their Information Encryption Applications

Photochromic hydrogen-bonded organic\nframeworks (HOFs)\ncan introduce\ndifferent luminescent functional groups to achieve synergistic controlled\nmultiple color change properties, which are in great demand for diverse\ninformation encryption applications. We report in this paper switchable\nphotochromic and photoluminescent dual luminescent functional group\nHOFs constructed with synergistic effects by <i>N</i>,<i>N</i>′-bis(2-phenylalanine)-1,4,5,8-naphthalenediimine\n(H<sub>2</sub>PheNDI) and benzenecarboximidamide 4,4′-azobis(hydrochloride)\n(AZBH). The crystal powder of <b>iHOF-41</b> is orange–red\nin color, which can be changed to black under the irradiation of a\n365 nm ultraviolet (UV) light source for 15 min. The photoisomerization\nrate of the crystal solution under continuous UV irradiation for 5\nh was close to 99%. The composite membranes can achieve the properties\nof photochromism and photoluminescence when they are discolored under\n365 nm UV irradiation and, at the same time, excite red bright fluorescence.\nThis work achieves the construction of HOFs based on switching biluminescent\nfunctional groups and explores the synergistic mechanism of the photoisomerization\nprocess and photochromism as well as its practical application in\ninformation encryption.