Highly luminescent hetero-ligand MOF nanocrystals with engineered massive Stokes shift for photonic applications.

Abstract

A high efficiency emission with a massive Stokes shift is obtained by fluorescent conjugated acene building blocks arranged in nanocrystals. The two ligands of equal molecular length and connectivity, yet complementary electronic properties, are co-assembled by zirconium oxy-hydroxy clusters, generating highly crystalline hetero-MOF nanoparticles The fast diffusion of singlet molecular excitons in the framework, coupled with the fine matching of ligands absorption and emission properties, enables to achieve an ultrafast activation of the low energy emission by diffusion-mediated non-radiative energy transfer in the 100 ps time scale, by using a low amount of co-ligands. This allow to obtain MOF nanocrystals with a fluorescence quantum efficiency of ̴ 70% and an actual Stokes shift as large as 750 meV. This large Stokes shift suppresses the reabsorption of fast emission issues in bulk devices, pivotal for a plethora of applications in photonics and photon managing spacing from solar technologies, imaging, and detection of high energy radiation. These features allowed to realize a prototypal fast nanocomposite scintillator that shows an enhanced performance with respect to the homo-ligand nanocrystals, achieving benchmark. values which compete with those of some inorganic and organic commercial systems.

Photo-functionalized metal–organic frameworks for anti-counterfeiting applications

“…3a, Perego et al used two fluorescent ligands and zirconium oxygen clusters to form MOF nanocrystals with excellent fluorescence efficiency with the same connectivity and length (9,10-diphenyl-antracenedicarboxylate (DPA) and 5,12-diphenyl-tetracenedicarboxylate (DPT)). 53 Benefitting from the emission of anthracene matching the absorption of tetrobenzene monomer, MOFs can achieve 97% energy transfer efficiency and 60% fluorescence quantum yield. However, high-density aggregation of ligands in rigid MOF structures often leads to self-quenching.…”

Nanographene-based Metal-Organic Frameworks for Engineering Energy Transfer Pathways

“…In particular, we envisioned that UMOF-2, assembled through a mixed-linker strategy of HPB and HBC linkers could exhibit efficient energy transfer between the linkers, LLET, due to the strong spectral overlap features with identical molecular length and connectivity, referring to previously reported studies. 40,44,45 To examine the photophysical properties of HPB and HBC linkers, the absorption and emission spectra were investigated in DMF solution. (Figure 3a and b, with photophysical parameters summarized in Table S2).…”

“…We find that nanographene-based 3D MOFs are excellent materials for the exploration of energy transfer phenomena because such systems can fine-tune fluorescence by avoiding aggregation-caused quenching (ACQ) in the framework. 32,37,38 Due to the atomically precise nature of frameworks, exact distance (and angle) information is readily available, which may help to understand the intricate photophysical processes and pathways, [39][40][41][42][43][44][45][46][47] ultimately unveiling the intrinsic structure-property correlation of nanographene in the framework. Interestingly, the selection of metal ions plays a crucial role in energy transfer within MOF structures.…”