Enhancement of Long-Lived Persistent Room-Temperature Phosphorescence and Anion Exchange with I^– and SCN^– via Metal–Organic Hybrid Formation

Abstract

An in-depth understanding of structure–property relationships and the construction of multifunctional stimuli-responsive materials are still difficult challenges. Herein, we discovered a 4,4′-bipyridinium derivative with both photochromism and dynamic afterglow at 77 K for the first time. A one-dimensional (1D) Cd­(II) coordination polymer (1) assembled by only a 4,4′-bipyridinium derivative and cadmium chloride showed photochromism, room-temperature phosphorescence (RTP), and electrochromism. Interestingly, we found that 1 underwent single-crystal-to-single-crystal transformation during the anion exchange process, and the color of the crystal changed from colorless to yellow (1-SCN – ) within 10 min. Complex 1 exhibited photochromism, whereas 1-SCN – did not. The difference in the photochromic behavior between the two complexes was ascribed to the electron transfer pathway between the carboxylate groups and viologen. The DFT calculation based on the crystal structure of 1-SCN – indicated that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were mainly located on bipyridine and cadmium atoms, eliminating the possibility of electron transfer, whereas for complex 1, electron transfer was probable from O and Cl atoms to pyridinium N atoms in viologen as demonstrated by density of states (DOS) calculations. In addition, complex 1 was successfully made into test paper for the rapid detection of I– and SCN– and displayed potential applications in inkless printing, multiple encryption, and anticounterfeiting.

Light‐Induced Electron Transfer Toward On/Off Room Temperature Phosphorescence in Two Photochromic Coordination Polymers

“…However, only a few electron transfer photochromic complexes were reported with RTP properties. [25,55,56] To achieve the switchable RTP behavior with this electron transfer photochromism, the structural factors with electron transfer and RTP activity is deserving prior attention. Suitable electron donor/acceptor units should be selected in the construction of electron transfer photochromic complexes, and a special organic phosphor should be incorporated into the photochromic complexes to achieve the RTP function.…”

Photo‐Controllable Ultralong Room‐Temperature Phosphorescence: State of the Art

“… [20–23] Moreover, the photo‐stimulus switchable RTP is mainly associated with the changes in chemical structure or absorbance induced by photo‐irradiation. These results have been proved in several pyridine‐based MOCs as reported by our group, [20] Zheng's group [21–25] and Wang's group [26,27] …”

Series of Viologen-Based Metal–Organic Polyhedra with Photo/Electrochromic Behavior for Inkless Printing and UV Detection

“…A possible strategy to fabricate sr-MOPs is incorporating photoactive organic ligands with lanthanide ions under acidic conditions. Among the photoactive moiety, viologen derivatives as typical representatives have been widely used in the field of chromic materials due to their extraordinary redox activity and good modifiability. − In addition, the radicals generated from external stimuli could trigger the coupling interaction with lanthanide ions, causing significant changes in the luminescence, , magnetic, − catalytic, , and electrical behavior, − which provides an ideal platform for the construction of smart responsive materials. Indeed, our group and several others have reported a few crystalline molecular materials whose physical properties can be controlled by photoirradiation. − Though these materials offer promising applications in optical switching devices and optical switches as well as other frontier areas, they are hampered by complicated external environments due to the need for multiple stimulus responses.…”

“…Among the photoactive moiety, viologen derivatives as typical representatives have been widely used in the field of chromic materials due to their extraordinary redox activity and good modifiability. 15−19 In addition, the radicals generated from external stimuli could trigger the coupling interaction with lanthanide ions, causing significant changes in the luminescence, 20,21 magnetic, 22−24 catalytic, 25,26 and electrical behavior, 26−28 which provides an ideal platform for the construction of smart responsive materials. Indeed, our group and several others have reported a few crystalline molecular materials whose physical properties can be controlled by photoirradiation.…”