Syntheses And Property Modulation Of Photochromic Metal-Organic Frameworks Materials

Photochromic materials have manifested promising prospects for applications in optical memory devices, bioluminescence detection, molecular switches, military camouflage concealment and optical security identification because they can change their color after irradiation. Such materials mostly focused on inorganic-organic hybrid materials and non-porous coordination polymer. Their host structure usually tends to change with changed-template, the photochromic behavior and other property can not be regulated flexibly. Metal-organic framework materials (MOFs) as a very promising class of organic - inorganic hybrid materials, has been widespread concern in the last two decades because of excellent structural tunability. This paper select micro-porous MOFs for the study. Photochromic viologen molecules was locked within micro-porous MOFs. Herein, four Photochromic MOFs (PMOFs) was synthesized by regulating different host-guest interaction through change different host frameworks and viologen cations. Two PMOFs [In6(BTC)8]·(MV)3 (1) and [In(BPDC)2]2(MV)·4DMF (2) were constructed by methyl viologen cation (MV2+) as guest and different anion frameworks as host which assembled by In3+ and BTC or BPDC. We found a strong ?-? interaction between BPDC and MV2+ in compound 2, this contribute to radical stability and the reversible photochromic behavior. On the contrary, compound 1 was lacking of host-guest interaction, its photochromism was irreversible, and C-N bond cleavage on methyl violet was accompanied by photochromism which derived from radical generated by irradiation. As the same time, the influence of radical on adsorption properties was discussed briefly. Another two PMOFs [In6(BTC)8](EV)3 (3) and [In6(BTC)8](BzV)3 (4) were constructed by the same anion framework with compound 1 but different viologen cations ethyl viologen (EV) and benzyl viologen (BzV). The photochromism of Compound 3 was similar to Compound 1, but Compound 4 exhibited reversible wavelength-dependent photochromism in room temperature. After on the irradiation of UV (3650 A), Soft X-ray (Cu-Ka,1.5418 A) and Hard X-ray (Mo-Ka,0.71073 A), it exhibited different color. So it was a desirable material for differentiating Hard/Soft X-ray by the naked eye in room temperature. Besides, a novel two-dimensional NDI-PMOF [Zn(DTz-NDI)(DMF)2] (5) was constructed by the ligand which linked by 1,4,5,8-naphthalene dianhydride and 5-amino-tetrazole, and its fluorescent can modulate by photochromic process. This paper based on structure feature and construct principle of micro-porous MOFs provide a agile, structure controlled, photochromism adjustable strategy for photochromic materials.