Fig. 7: MOF films with anisotropic fluorescence and controlled micropore alignment.
From: Low-dimensional assemblies of metal-organic framework particles and mutually coordinated anisotropy
a Schematics showing DMASM dye molecules (orange rods) selectively recruited on (002) facets of MIL-96 particles (Step 1). The molecular structure of the dye is shown, and its transition dipole moment is labeled with black double arrow. The randomly oriented dye molecules in solution are encapsulated in the ellipsoidal pores of MIL-96 (structure shown) and their transition dipole moments are aligned to the pore (the [002] direction, purple double arrow). The dye-encapsulated particles (MIL-96-2) with random orientations are assembled to form MOF films with mutually oriented dye arrays (Step 2). The side view of dye orientation (angle with respect to substrate is 42°) and their spatial arrangement in a centered rectangular lattice are shown. b, c Fluorescence microscope images of dye-encapsulated MIL-96-2 particles before (b) and after (c) self-assembly. Inset (b) shows a large MIL-96 particle with fluorescence located at the (002) faces; inset c is the zoomed-in MOF film. d Illustration of the angle-dependent emission of MIL-96-2 films excited by linearly polarized light (blue double arrows). The direction of polarization is parallel (left) and perpendicular (right) to the dye orientation to turn on and off the emission. e Azimuthal plot of the fluorescence intensities (IFl) of MIL-96-2 films as a function of θ, angle between polarization direction and dye orientation (also c axis of MIL-96). f Representative fluorescence images show strong, intermediate, and weak fluorescence of the MIL-96-2 film in response to the polarized light at θ of 0°, 45° and 90°. g Fluorescence image displays grains of MIL-96-2 film with diverse orientations and their boundaries (yellow dotted lines). Scale bars: 5 μm (b, c, f, g), 2 μm (b, inset), and 1 μm (c, inset).
