Linker Engineering toward Full-Color Emission of UiO-68 Type Metal–Organic Frameworks

Abstract

Luminescent metal–organic frameworks (LMOFs) demonstrate strong potential for a broad range of applications due to their tunable compositions and structures. However, the methodical control of the LMOF emission properties remains a great challenge. Herein, we show that linker engineering is a powerful method for systematically tuning the emission behavior of UiO-68 type metal–organic frameworks (MOFs) to achieve full-color emission, using 2,1,3-benzothiadiazole and its derivative-based dicarboxylic acids as luminescent linkers. To address the fluorescence self-quenching issue caused by densely packed linkers in some of the resultant UiO-68 type MOF structures, we apply a mixed-linker strategy by introducing nonfluorescent linkers to diminish the self-quenching effect. Steady-state and time-resolved photoluminescence (PL) experiments reveal that aggregation-caused quenching can indeed be effectively reduced as a result of decreasing the concentration of emissive linkers, thereby leading to significantly enhanced quantum yield and increased lifetime.

Tuning and Directing Energy Transfer in the Whole Visible Spectrum through Linker Installation in Metal–Organic Frameworks

“…Both HOMO and LUMO of HIAM-4001 resemble those of the BTTC linker without any contribution from Zr metal, which is similar with our previous work. [36] Agradual bathochromicshift was observed in the UV-vis absorption spectra from HIAM-4000 to HIAM-4004, which is also consistent with their corresponding emission energies (Figure 2e). It should be noted that HIAM-4003 and HIAM-4004 exhibit am uch broader light absorption range,which could be used as bluelight excitable phosphors or photocatalysts.A ll five HIAM-400X compounds show excellent thermal stability with the framework remaining intact up to % 500 8 8C( Figure S6).…”

“…As shown in Figure 2b,t he PXRD patterns of the assynthesized HIAM-400X compounds exhibit an excellent agreement with the simulated patterns of HIAM-4001, confirming their isoreticular nature as well as the phase purity.T he solid-state PL spectra and the transient PL decay of HIAM-400X show similar trend as observed for UiO-68 type MOFs with the same Ar core (Figure 2c and d). [36] Tu nable emission from blue to red was recorded for HIAM-400X with peak maxima at 470, 505, 522, 595 and 645 nm for HIAM-4000, HIAM-4001, HIAM-4002, HIAM-4003 and HIAM-4004, respectively,w hich is consistent with the emissive colors of their single-crystals (Figure 2a and c). The corresponding PL quantum yields (PLQYs) of the HIAM-4000 to HIAM-4004 are 21.1 %, 44.0 %, 28.4 %, 17.6 %a nd 7.70 %u nder 365 nm excitation.…”

“…As expected, the emissions from DTTC to NSTC cover the whole visible light range from blue to red (Figure S1), which is similar to what we have observed in linkers with the same Ar core in our previous work. [36] Density functional theory (DFT) was utilized to calculate the molecular orbital energies of the linkers.A sd epicted in Figure S2, the highest occupied molecular orbital (HOMO) energies gradually increases while the lowest unoccupied molecular orbital (LUMO) energies monotonically decreases from DTTC to NSTC, resulting in ad ecrease of HOMO-LUMO energy gap, consistent with the observed emission energies and previously reported work. [37,38] Scheme 1.…”

“…Them ain challenge lies in synthesizing organic linker-based full-color emissive MOFs or second linkers,and tuning the ET in the whole visible spectrum. We have recently discovered that full-color emissive UiO-68 type MOFs can be prepared using 2,1,3-benzothiadiazole and its derivative-based dicarboxylic acids, [36] which inspires us to extend this strategy to the design of LMOFs with multi-fold tunability using similar organic linkers to systematically control and direct ET process.…”

Encapsulation of Dyes in Luminescent Metal-Organic Frameworks for White Light Emitting Diodes

“…From fundamental views, it is necessary to develop novel organic dyes and MOF structures considering factors such as topology, luminescence, charge transfer and stability. Moreover, in-depth research on mechanism Recently, Liu and Li applied a mixed-linker strategy to successfully synthesize a series of UiO-68 MOFs with full color emission by changing the ratios of chromophore and non-fluorescent linkers [59]. Obviously, introducing of non-fluorescent linkers is helpful in reducing the concentration of emissive linkers and increasing the spatial distances between fluorescent linkers, which effectively suppresses the π-π stacking interactions and thus enhances the emission efficiency.…”