Zirconium Metal–Organic Frameworks Containing a Biselenophene Linker: Synthesis, Characterization, and Luminescent Properties

Abstract

The bicyclic ditopic linker 2,2′-biselenophene-5,5′dicarboxylic acid (H 2 SpSp), specifically designed for metal−organic framework (MOF) construction, has been synthesized in good yield and fully characterized. The corresponding zirconium MOF (Zr-MOF) [Zr 6 O 4 (OH) 4 (SpSp) 3.8 Cl 4.4 ] (1; where missing linkers are replaced by chloride anions as shown by X-ray fluorescence and elemental analysis) is isostructural with its bithiophene and bithiazole analogues. Starting from 1, an extension of the biselenophene-based Zr-MOF family has been successfully achieved, exploiting the structural analogy of the fivemembered heterocycles selenophene, thiophene, and thiazole. Thus, three mixed-linker MOFs containing variable amounts of different bis(heterocyclic) dicarboxylic acids have been prepared and fully characterized: the two double-mixed [Zr 6 O 4 (OH) 4 (SpSp) 2.6 (TpTp) 1.3 Cl 4.2 ] (2; H 2 TpTp = 2,2′-bithiophene-5,5′-dicarboxylic acid) and [Zr 6 O 4 (OH) 4 (SpSp) 2 (TzTz) 1.8 Cl 4.4 ] (3; H 2 TzTz = 2,2′-bithiazole-5,5′-dicarboxylic acid) materials, as well as the triple-mixed [Zr 6 O 4 (OH) 4 (SpSp) 1.6 (TpTp) 1.2 (TzTz) 1.4 Cl 3.6 ] (4) compound. The four MOFs are luminescent under UV irradiation, exhibiting emission wavelengths falling in the blue-green visible region, as observed for their constitutive linkers. These materials open new horizons in the preparation of porous luminescent sensors or multicolor emitters for light-emitting diodes.

Nanoporous Organic Frameworks as Light-Emitting Diodes: A Review

“…13,36 In addition, solid-state luminescence has shown great challenges in practical applications due to relatively low photoluminescence quantum yield (PLQY) values as a result of quenched fluorescence, aggregation, and phase separation. 37 The assembly and dispersion of molecules in rigid frameworks can tackle the issue by eliminating their aggregation, thus enhancing the luminescence of solid-state materials. Different porous materials have already been reported in LED applications, including silver nanoclusters confined in zeolites, 38 rare-earth-ion-doped porous glass ceramics, 39 porous silicon, 40 porous graphene, 41 and porous polymer films.…”

“…In traditional GaN LED chips, the large difference in the refractive indexes between GaN and air encloses most of the emitted light in the reflecting cavity by total internal reflection (TIR), and at least 18% of the produced light is reflected by the cavity back into the chip rather than being scattered around . Porous materials allow the scattering of photons, thus lowering the TIR and increasing the transmission of light, creating a greater light extraction capacity with respect to traditional LEDs. , In addition, solid-state luminescence has shown great challenges in practical applications due to relatively low photoluminescence quantum yield (PLQY) values as a result of quenched fluorescence, aggregation, and phase separation . The assembly and dispersion of molecules in rigid frameworks can tackle the issue by eliminating their aggregation, thus enhancing the luminescence of solid-state materials.…”