Competitive Excimer Formation and Energy Transfer in Zr‐Based Heterolinker Metal–Organic Frameworks

Abstract

The spectroscopy and dynamics of a series of Zr-based MOFs in dichloromethane suspension are reported. These Zr-NADC MOFs were constructed by using different mixtures of 2,6-naphthalenedicarboxylate (NDC) and 4-amino-2,6-naphthalenedicarboxylate (NADC) as organic linkers. The fraction of NADC relative to NDC in these heterolinker MOFs ranges from 2 to 35 %. The results indicate two competitive photoprocesses: NDC excimer formation and an energy transfer (ET) from excited NDC linkers to NADC linkers. Increasing the fraction of NADC linkers in the Zr-NADC nanostructure decreases the mean time constant of NDC excimer formation, while the NADC emission intensity experiences a drop at the highest fraction of this linker in the MOF. The first observation is explained by an increase in the energy-transfer probability between the two linkers, and the second by emission quenching in the NADC linkers due to ultrafast charge transfer assisted by the amino group. Femtosecond time-resolved emission studies showed that the ET process (recorded as decaying and rising components) from excited NDC to NADC takes place in 1.2 ps. Direct excitation of the NADC linkers (at 410 nm) shows a decaying, but not rising, component of 250-480 fs, which could reflect the formation of a nonemissive charge-separation state. The results show that by using MOFs having heterolinkers it is possible to trigger and tune excimer formation and ET processes.

New OLEDs Based on Zirconium Metal‐Organic Framework

“…In this scenario, both, ET between the MOF and the fluorophores, and/or a recombination directly on the fluorophores can happen, allowing a change in the intensity and tunability of the emission color. It has been previously reported in several studies that for this particular MOF, the inclusion of C153 and DCM in the Zr‐NDC materials allows efficient ET from the NDC linkers to the dyes, modifying the color from blue to yellow or even white light emission, respectively . Although the ET could be affected by the surrounding environment, our present photophysical study shows that when going from a neat MOF in the solid to a MOF dispersed in a PS matrix, the extension of the ET is not altered, suggesting the use of C153@Zr‐NDC and DCM@Zr‐NDC composites as potential candidates to tune the color of the Zr‐MOFLEDs.…”

“…Previously, we have focused on the photoluminescence (PL) of Zr‐NDC MOF (Zr 6 O 4 (OH) 4 (NDC) 12 ), which presents a high emission quantum yield (30%), and elucidated a ligand‐to‐cluster charge transfer (LCCT) process with the subsequent formation of a long‐lived charge‐separated state in the MOFs . These studies inspired us to fabricate and study a LED using this MOF as electroactive layer.…”

Understanding metal–organic frameworks for photocatalytic solar fuel production

“…70 In the case of very weak absorbance but reasonable fluorescence, this is usually done in an emission fashion. 71,72 Here, time-correlated single-photon counting (TCSPC) is the most popular method, measuring picosecond emission decays. For the case of femtosecond emission transients, the fluorescence up-conversion technique is often used.…”

RhB‐Embedded Zirconium–Naphthalene‐Based Metal–Organic Framework Composite as a Luminescent Self‐Calibrating Platform for the Selective Detection of Inorganic Ions

“…In addition, the red emission of the composites from R@D1 to R@D3 occurred with ap artial redshift (from 595 to 607 nm), which may be due to the enhanced interactions between RhB molecules with the increasing loading quantity.A ss hown in Figure 2b,a significant spectralo verlap between thea bsorption of RhB and emission of DUT-52 is observed, which illustrates the occurrence of resonance energy transfer from DUT-52 to RhB. [35][36][37] To further confirm this case, the fluorescence lifetime of the RhB@DUT-52 composites and RhB was measured by monitoring their individual red emission peaks ( Figure 2c). The lifetime is 11.60, 5.16, and 2.01 ns for the R@D1, R@D2, and R@D3 composites, respectively,w hereas this value is 1.43 ns for RhB in aqueous solution.T he longerl ifetimef or the RhB@DUT-52 composites further demonstratest he existence of resonance energy transfer from DUT-52 to RhB.…”

“…Notably,R hB in the solid state is nearly nonfluorescent due to an aggregation-induced quenching effect, and its solution shows concentration-dependent fluorescence( FiguresS6a nd S7, Supporting Information). [35][36][37] To further confirm this case, the fluorescence lifetime of the RhB@DUT-52 composites and RhB was measured by monitoring their individual red emission peaks (Figure 2c). With increasing encapsulation quantity of RhB, the peak-to-heightr atio of the two emissions changed continuously,i nw hich the intensity of the blue emission is weakeneda nd the red emission is strengthened.…”