Photochromism of metal–organic frameworks based on carbazole-dicarboxylic acid and bipyridine: sensing adjustment by controlling strut-to-strut energy transfer

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Abstract
In this paper, two energy-transfer photochromic metal–organic frameworks (MOFs) {[Zn(L)0.5(bpy)]·H2O·DMF}n (1) and {[Zn(L)0.5(bpe)]·2H2O·DMF}n (2) (H4L = 9,9′-(1,4-phenylenebis(methylene))bis(9H-carbazole-3,6-dicarboxylic acid), bpy = 4,4′-bipyridine, bpe = 4,4′-vinylenedipyridine) were designed and synthesized. Both 1 and 2 showed similar pillared-paddle wheel type frameworks with bpy and bpe as the chromophore, respectively, and L4− as the antenna-type light harvester, yielding strut-to-strut energy transfer (antenna behavior) within the well-ordered structures. Among them, 1 displayed excellent energy-transfer photochromic behavior under UV light accompanied by color transformation from colorless to purple. In addition, the photochromic behavior of 1 has obvious, fast, controllable and reversible characteristics. On the other hand, 2 showed a different energy-transfer photochromic behavior in the aspects of color changing, gamut, and sensitivity. The variation has been ascribed to the substitution of chromophore bpy in 1 with bpe in 2, which influences the efficiency of energy transfer within the MOFs. Therefore, with the structural diversity and tunability of MOFs, the sensitivity, color, and gamut of energy-transfer of the photochromic MOFs can be tuned by the appropriate choice of the constitutions of MOFs. This work will provide useful guidance for developing novel energy-transfer photochromic MOF materials.
Funding Information
  • National Natural Science Foundation of China (21771163, 21671174)
  • Zhengzhou University (2019cxcy474)

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