Surface-anchored Metal-organic Frameworks Research Articles

Regulated Charge Transfer in Donor-Acceptor Metal-Organic Frameworks for Highly-Sensitive Photodetectors.

In photo-induced charge separation, organic thin films with donor and acceptor chromophores are vital for uses such as artificial photosynthesis and photodetection. The main challenges include optimizing charge separation efficiency and identifying the ideal acceptor/donor ratio. Achieving this is difficult due to the variability in molecular configurations within these typically amorphous organic aggregates. Metal-organic frameworks (MOFs) provide a structured solution by enabling systematic design of donor/acceptor blends with adjustable ratios within a crystalline lattice. We demonstrate this approach by incorporating donor and acceptor naphthalenediimide (NDI) chromophores as linkers in a highly oriented, monolithic MOF thin film. By adjusting the NDI acceptor linker concentration during the layer-by-layer assembly of surface-anchored MOF thin films (SURMOFs), we significantly enhanced charge separation efficiency. Surprisingly, the optimum acceptor concentration was only 3%, achieving a forty-fold increase in photodetection efficiency compared to baseline NDI donor-based SURMOFs. This unexpected behaviour was clarified through theoretical analysis enabled by the well-defined crystalline structure of the SURMOFs. Using density functional theory and kinetic Monte Carlo simulations, we identified two opposing effects from acceptors: the positive effect of suppressing undesirable charge carrier recombination is offset at high concentrations by a reduction in charge-carrier mobility.

Electrochromic, Surface-Anchored Metal-Organic Frameworks for Stabilized Silver Nanowire Flexible Transparent Electrodes.

Despite excellent optical and electrical properties, the brittleness of indium tin oxide (ITO), used as a transparent electrode, prevents the realization of stable flexible devices. If silver nanowire (AgNW) networks represent a promising alternative, their lack of thermal and electrochemical stability still prevents their fast development in numerous applications. Herein, we report a novel strategy consisting of the deposition of an electrochromic and protective layer of oriented hybrid materials, also known as surface-anchored metal-organic frameworks (SurMOFs). Furthermore, the dual role played by the SurMOF is achieved using a room-temperature and low-cost method for the efficient use of bare AgNWs. A step forward was achieved by demonstrating electrochemical and mechanical stability for flexible electrochromic SurMOF@AgNW/PET thin films, switching reversibly from orange (+0.2 V) to blue (-0.8 V) in 8.4 s and 10.4 s, respectively, with a color efficiency of 158 cm2/C after being bent 300 times.

External Electric Field Control of Exciton Motion in Porphyrin-Based Metal Organic Frameworks.

Porphyrins are excellent light-harvesting complexes. Presently they are unsuitable for photovoltaic applications, as their excellent light absorbance is compensated to a large extent by their poor transport properties, where most excitons are lost by recombination. Arranging porphyrins in regular, strongly bound, lattices of surface-anchored metal-organic frameworks (PP-SURMOFs) may facilitate charge carrier dissociation, but does not significantly enhance the conductive properties. In most cases, photogenerated excitons traverse undirected, Brownian motion through a hopping process, resulting in a substantial diffusion length to reach electrodes, leading to significant exciton loss through recombination. Here, we propose to guide exciton diffusion indirectly by an external electric field. We show that electric fields, even as strong as 1 V nm-1, do not affect the HOMO-LUMO gap of the porphyrins. However, fields of 0.1 V nm-1 and even less demonstrate a notable Stark effect, with slight band gap reductions, for some PP-SURMOFs. When applied as an electric field gradient, for instance, via the substrate, it creates a unidirectional hopping pathway for the excitons. Consequently, we expect a significant reduction of exciton diffusion length leading to increased utilization of photogenerated excitons as they reach the electrodes. This strategy holds promise for integrating photoactive molecules in photovoltaic and photocatalytic applications.

Metal‐organic Frameworks in Semiconductor Devices

AbstractMetal‐organic frameworks (MOFs) are a specific class of hybrid, crystalline, nano‐porous materials made of metal‐ion‐based ‘nodes’ and organic linkers. Most of the studies on MOFs largely focused on porosity, chemical and structural diversity, gas sorption, sensing, drug delivery, catalysis, and separation applications. In contrast, much less reports paid attention to understanding and tuning the electrical properties of MOFs. Poor electrical conductivity of MOFs (~10−7–10−10 S cm−1), reported in earlier studies, impeded their applications in electronics, optoelectronics, and renewable energy storage. To overcome this drawback, the MOF community has adopted several intriguing strategies for electronic applications. The present review focuses on creatively designed bulk MOFs and surface‐anchored MOFs (SURMOFs) with different metal nodes (from transition metals to lanthanides), ligand functionalities, and doping entities, allowing tuning and enhancement of electrical conductivity. Diverse platforms for MOFs‐based electronic device fabrications, conductivity measurements, and underlying charge transport mechanisms are also addressed. Overall, the review highlights the pros and cons of MOFs‐based electronics (MOFtronics), followed by an analysis of the future directions of research, including optimization of the MOF compositions, heterostructures, electrical contacts, device stacking, and further relevant options which can be of interest for MOF researchers and result in improved devices performance.

Insight into the generation of near infra-red (NIR) absorbing species in electrochromic surface-anchored metal-organic frameworks.

Due to their versatility and easy processing, Surface-Anchored Metal-Organic Frameworks (SurMOFs) have gained interest in recent times as promising electrochromic thin films. Herein a step forward in their use and characterization was achieved thanks to the integration of {Zn2(PDICl4)2} SurMOFs in a multi-layer electrochromic device (ECD), based on a membrane-like electrolyte. The optical and electrochemical properties of the ECD were fully characterized, revealing a two-step reduction process localized on the organic ligand and involving subsequent near infra-red (NIR) and cyan absorbing states, leading to optical modulation of the films. The species responsible for this absorption were isolated and identified in the reduced states. In parallel to experimental characterization, quantum chemistry was successfully used to investigate the structure-property relationship of the SurMOF, revealing additional information regarding the structure and the local environment of the electrochromic ligand.

001]-Oriented heteroepitaxy for fabricating emissive surface mounted metal–organic frameworks

A hybrid SURMOF with specific crystallographic [001] orientation is fabricated via step-by-step liquid-phase heteroepitaxial method. The preferential [001] orientation of Cu2(BDC)2(DABCO) is retained via Zn2(BDC)2(DABCO) to Zn2(ADC)2(BPy).

Fast Dynamic Synthesis of MIL-68(In) Thin Films in High Optical Quality for Optical Cavity Sensing.

Fabrication of metal-organic framework (MOF) thin films rigidly anchored on suitable substrates is a crucial prerequisite for the integration of these porous hybrid materials into electronic and optical devices. Thus, far, the structural variety for MOF thin films available through layer-by-layer deposition was limited, as the preparation of those surface-anchored metal-organic frameworks (SURMOFs) has several requirements: mild conditions, low temperatures, day-long reaction times, and nonaggressive solvents. We herein present a fast method for the preparation of the MIL SURMOF on Au-surfaces under rather harsh conditions: Using a dynamic layer-by-layer synthesis for MIL-68(In), thin films of adjustable thickness between 50 and 2000 nm could be deposited within only 60 min. The MIL-68(In) thin film growth was monitored in situ using a quartz crystal microbalance. In-plane X-ray diffraction revealed oriented MIL-68(In) growth with the pore-channels of this interesting MOF aligned parallel to the support. Scanning electron microscopy data demonstrated an extraordinarily low roughness of the MIL-68(In) thin films. Mechanical properties and lateral homogeneity of the layer were probed through nanoindentation. These thin films showed extremely high optical quality. By applying a poly(methyl methacrylate) layer and further depositing an Au-mirror to the top, a MOF optical cavity was fabricated that can be used as a Fabry-Perot interferometer. The MIL-68(In)-based cavity showed a series of sharp resonances in the ultraviolet-visible regime. Changes in the refractive index of MIL-68(In) caused by exposure to volatile compounds led to pronounced position shifts of the resonances. Thus, these cavities are well suited to be used as optical read-out sensors.

Broadband Dielectric Spectroscopic Detection of Aliphatic Alcohol Vapors with Surface-Mounted HKUST-1 MOFs as Sensing Media

We leveraged chemical-induced changes to microwave signal propagation characteristics (i.e., S-parameters) to characterize the detection of aliphatic alcohol (methanol, ethanol, and 2-propanol) vapors using TCNQ-doped HKUST-1 metal-organic-framework films as the sensing material, at temperatures under 100 °C. We show that the sensitivity of aliphatic alcohol detection depends on the oxidation potential of the analyte, and the impedance of the detection setup depends on the analyte-loading of the sensing medium. The microwaves-based detection technique can also afford new mechanistic insights into VOC detection, with surface-anchored metal-organic frameworks (SURMOFs), which is inaccessible with the traditional coulometric (i.e., resistance-based) measurements.

Stability of Monolithic MOF Thin Films in Acidic and Alkaline Aqueous Media.

In the context of thin film nanotechnologies, metal-organic frameworks (MOFs) are currently intensively explored in the context of both, novel applications and as alternatives to existing materials. When it comes to applications under relatively harsh conditions, in several cases it has been noticed that the stability of MOF thin films deviates from the corresponding standard, powdery form of MOFs. Here, we subjected SURMOFs, surface-anchored MOF thin films, fabricated using layer-by layer methods, to a thorough characterization after exposure to different harsh aqueous environments. The stability of three prototypal SURMOFs, HKUST-1, ZIF-8, and UiO-66-NH2 was systematically investigated in acidic, neutral, and basic environments using X-ray diffraction and electron microscopy. While HKUST-1 films were rather unstable in aqueous media, ZIF-8 SURMOFs were preserved in alkaline environments when exposed for short periods of time, but in apparent contrast to results reported in the literature for the corresponding bulk powders- not stable in neutral and acidic environments. UiO-66-NH2 SURMOFs were found to be stable over a large window of pH values.

In situ Nanoscale Infrared Spectroscopy of Water Adsorption on Nanoislands of Surface‐Anchored Metal‐Organic Frameworks

AbstractDespite technological advancements, probing gas‐solid interfaces at the nanoscale is still a formidable challenge. New nano‐spectroscopic methods are needed to understand the guest–host interactions of functional materials during gas sorption, separation, and conversion. Herein, we introduce in situ Photoinduced Force Microscopy (PiFM) to evidence site‐specific interaction between Metal‐Organic Frameworks (MOFs) and water. To this end, we developed amphiphilic Surface‐anchored MOF (SURMOF) model systems using self‐assembly for the side‐by‐side hetero‐growth of nanodomains of hydrophilic HKUST‐1 and hydrophobic ZIF‐8. PiFM was used to probe local uptake kinetics and to show D2O sorption isotherms on (defective) HKUST‐1 paddlewheels. By monitoring defect vibrations, we visualized in real‐time the saturation of existing defects and the creation of D2O‐induced defects. This work shows the potential of in situ PiFM to unravel gas sorption mechanisms and map active sites on functional (MOF) materials.

In situ Nanoscale Infrared Spectroscopy of Water Adsorption on Nanoislands of Surface-Anchored Metal-Organic Frameworks.

Despite technological advancements, probing gas‐solid interfaces at the nanoscale is still a formidable challenge. New nano‐spectroscopic methods are needed to understand the guest–host interactions of functional materials during gas sorption, separation, and conversion. Herein, we introduce in situ Photoinduced Force Microscopy (PiFM) to evidence site‐specific interaction between Metal‐Organic Frameworks (MOFs) and water. To this end, we developed amphiphilic Surface‐anchored MOF (SURMOF) model systems using self‐assembly for the side‐by‐side hetero‐growth of nanodomains of hydrophilic HKUST‐1 and hydrophobic ZIF‐8. PiFM was used to probe local uptake kinetics and to show D2O sorption isotherms on (defective) HKUST‐1 paddlewheels. By monitoring defect vibrations, we visualized in real‐time the saturation of existing defects and the creation of D2O‐induced defects. This work shows the potential of in situ PiFM to unravel gas sorption mechanisms and map active sites on functional (MOF) materials.

Crystalline assembly of perylene in metal–organic framework thin film: J-aggregate or excimer? Insight into the electronic structure

The spatial orientation of chromophores defines the photophysical and optoelectronic properties of a material and serves as the main tunable parameter for tailoring functionality. Controlled assembly for achieving a predefined spatial orientation of chromophores is rather challenging. Metal–organic frameworks (MOFs) are an attractive platform for exploring the virtually unlimited chemical space of organic components and their self-assembly for device optimization. Here, we demonstrate the impact of interchromophore interactions on the photophysical properties of a surface-anchored MOF (SURMOF) based on 3,9-perylenedicarboxylicacid linkers. We predict the structural assembly of the perylene molecules in the MOF via robust periodic density functional theory calculations and discuss the impact of unit topology and π–π interaction patterns on spectroscopic and semiconducting properties of the MOF films. We explain the dual nature of excited states in the perylene MOF, where strong temperature-modulated excimer emission, enhanced by the formation of perylene J-aggregates, and low stable monomer emission are observed. We use band-like and hopping transport mechanisms to predict semiconducting properties of perylene SURMOF-2 films as a function of inter-linker interactions, demonstrating both p-type and n-type conduction mechanisms. Hole carrier mobility up to 7.34 cm2 Vs−1 is predicted for the perylene SURMOF-2. The results show a promising pathway towards controlling excimer photophysics in a MOF while controlling charge carrier mobility on the basis of a predictive model.

(Invited) The Interplay of Conformation and Electronic Structure in Metal Organic Frameworks

Metal organic frameworks (MOFs) have emerged as a versatile class of designer crystals with tunable properties. Due to their vast chemical composition space and key importance of molecular structure and organization on their electronic properties, modelling and simulation are essential to understand and to optimize MOF functionality. Here, we show that multiscale models that combine structural simulations with electronic structure calculations can be used to explain the origin of the photophysical and conducting behavior of MOF films as the function of their nano/microscale morphology and to tune the specific property by predictive crystal engineering.Using the density functional theory formalism and our in-house ab initio method, we investigate efficient excited-state transport properties of porphyrin SURMOF [1] and photoconduction of MOF with embedded acceptors like C60 [2]. We predict the charge transport and mobility in polycyclic aromatic hydrocarbons based on the surface-anchored metal-organic frameworks (SURMOF) as a function of the type of the organic linker. We show the reason for the improved conductivity as derived from the spatially ordered structure of a material and confirm the charge transfer anisotropy through the detailed analysis of the transfer rates for electron and hole transport.To achieve unprecedented PL quantum yields for crystalline core-substituted naphthalenediimides (cNDIs) MOF, we determined the optimal alignment of chromophoric linkers to yield highly emissive J-aggregates [3]. We tuned the molecular alignment of linkers by introducing adjustable “steric control units” (SCUs) controlling the excitonic coupling and computationally screened the large library of handle-equipped MOF chromophoric linkers and for the best SCUs.Together with experimental observations, we prove that ab initio calculations enable valuable predictions of new promising candidates for emitting and/or semiconducting organic materials made in spatially ordered fashion in the SURMOF. Our data demonstrates the feasibility of MOF-based crystal engineering approaches that can be universally applied to tailor the materials properties.

Electron Beam-Induced Surface Activation of Metal–Organic Framework HKUST-1: Unraveling the Underlying Chemistry

The local chemical activation of surface-anchored metal–organic frameworks is a novel electron beam-based lithographic technique with a high potential for the fabrication of chemically and spatially well-defined nanostructures in the sub-10 nm regime. In this context, we have performed a detailed investigation of electron beam-induced surface activation (EBISA) on the surface-anchored layers of HKUST-1 and copper(II) oxalate with the subsequent autocatalytic growth (AG) of deposits from the precursors Fe(CO)5 and Co(CO)3NO. We use reflection absorption infrared spectroscopy and measurements on electron-stimulated desorption to identify the chemical species that trigger decomposition of the precursors on the activated surfaces. EBISA on HKUST-1 works for Fe(CO)5 but not for Co(CO)3NO and is therefore chemical selective. On the other hand, we demonstrate that copper(II) oxalate is not susceptible to EBISA for both precursors, ruling out that Cu nanoparticles are active sites for initiating AG. A detailed di...

Oxidative polymerization of terthiophene and a substituted thiophene monomer in metal-organic framework thin films

Films consisting of surface-anchored metal-organic frameworks (SURMOFs) which are prepared by layer-by-layer deposition techniques can be used as highly oriented crystalline template structures for oligomerization processes. Herein, SURMOF films of Zn(bdc) (1) and, Cu(bpdc) (2) were prepared, which consist of lamellar ordered 2D MOF sheets forming 1D channels as the host structures for oligomerization of terthiophene (Tth) and, 3,4-ethylenedioxythiophene (EDOT), respectively. After SURMOF preparation, the pores were filled either with Tth or EDOT and the oligomerization was initiated by oxidizing agents, such as I2 and FeCl3. Using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF/MS), the short chains of polyterthiophene (PTth) and poly(3,4-ethylenedioxythiophene) (PEDOT) were characterized. FT-IR and Raman spectroscopy further confirmed the presence of oligomers inside the pores of the SURMOFs. Using the SURMOF thin films as template, a homogeneously distributed conductive MOF-PEDOT composite coating can be achieved, with potential applications in optoelectronics.

Comparison of Surface-Bound and Free-Standing Variations of HKUST-1 MOFs: Effect of Activation and Ammonia Exposure on Morphology, Crystallinity, and Composition.

Metal-organic frameworks (MOFs) are extremely porous, crystalline materials with high surface area for potential use in gas storage, sequestration, and separations. Toward incorporation into structures for these applications, this study compares three variations of surface-bound and free-standing HKUST-1 MOF structures: surface-anchored MOF (surMOF) thin film, drop-cast film, and bulk powder. Herein, effects of HKUST-1 ammonia interaction and framework activation, which is removal of guest molecules via heat, are investigated. Impact on morphology and crystal structure as a function of surface confinement and size variance are examined. Scanning probe microscopy, scanning electron microscopy, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and energy dispersive X-ray spectroscopy monitor changes in morphology and crystal structure, track ammonia uptake, and examine elemental composition. After fabrication, ammonia uptake is observed for all MOF variations, but reveals dramatic morphological and crystal structure changes. However, activation of the framework was found to stabilize morphology. For activated surMOF films, findings demonstrate consistent morphology throughout uptake, removal, and recycling of ammonia over multiple exposures. To understand morphological effects, additional ammonia exposure experiments with controlled post-synthetic solvent adsorbates were conducted utilizing a HKUST-1 standard powder. These findings are foundational for determining the capabilities and limitation of MOF films and powders.

Dipolar Molecular Rotors in Surface-Anchored Metal Organic Frameworks

The functionalization of surfaces with molecular machines is highly interesting due to the vast field of applications. Transferring the function of individual molecules to a macroscopic scale by bringing a multitude of them to act collectively is essential for materializing new technologies. For this purpose, dipolar rotors can be put into a supra molecular structure to switch the light transmission of a material by changing their orientation. A high three-dimensional order can be achieved by using rotors as linkers in surface-anchored metal organic frameworks (SURMOFs).1-3 Crafted SURMOF thin films allow the alignment of the dipolar rotors in an external electric field.4 Making use of this behaviour, the transmission of light can be modulated with the application of the field and be investigated towards its uses in optical technologies. In this project, different organic linker molecules with permanent dipole moments are synthesized and used in SURMOF fabrication. Dielectric loss spectroscopy of the SURMOF thin films gives information about the dipole-dipole interaction within the layers and the alignment of rotors along the applied electric field.5 Devices are being constructed with a transparent top electrode for electric field application. Information gathered from the behaviour of first generation linker molecules will refine the molecule designs for the next generation so that the optical and electronic properties of the material can be tuned as desired. Shekhah, H. Wang, S. Kowarik, F. Schreiber, M. Paulus, M. Tolan, C. Sternemann, F. Evers, D. Zacher, R. A. Fischer, C. Woll, J. Am. Chem. Soc. 2007, 129, 15118-15119.-G. Gu, A. Pfriem, S. Hamsch, H. Breitwieser, J. Wohlgemuth, L. Heinke, H. Gliemann, C. Wöll, Microporous and Mesoporous Materials 2015, 211, 82-87.L. Zhuang, A. Terfort, C. Wöll, Coordination Chemistry Reviews 2016, 307, 391-424.Zheng, M. E. Mulcahy, D. Horinek, F. Galeotti, T. F. Magnera, J. Michl, J. Am. Chem. Soc. 2004, 126, 4540.D. Horansky, L. I. Clarke, J. C. Price, T.-A. V. Khuong, P. D. Jarowski, M. A. Garcia-Garibay, Physical Review B 2005, 72, 014302. Figure 1

Energy Transfer in Surface Anchored Metal-Organic Thin Films

To achieve high efficiency energy harvesting system, long range diffusion, reduced non-radiative paths, and directional transport are the key parameters to control. Organic polymers and organic-inorganic hybrids with certain nanostructures perform well in regard to diffusion length and directionality; however those often lack mesoscopic order. Hence, further investigations on long-range ordered crystalline structures are essential to improve exciton diffusion length and directionality. Here, I would like to demonstrate surface anchored metal-organic frameworks (SURMOFs) as a potential candidate to address anisotropic energy transport feature. These surface grown thin films possess following advantages over powder crystalline MOF structures/organic ordered films: a) These are highly crystalline and oriented; b) can be grown on any transparent conductive surface; c) films thickness and roughness can be controlled in a straight forward fashion; and d) heterostructures with organic-organic interface can be constructed; e.g. MOF-on-MOF structures [1-2]. A suitably constructed SURMOF-2, made of 4,4′-(anthracene-9,10-diyl)dibenzoicacid (ADB) linkers showed existence of two excited states, a monomer-like PLMon and an excimer-like PLExc. Both the excited states are found to be mobile and their diffusion and related anisotropy are studied using steady-state and time-resolved fluorescence spectroscopy. Constructing two different type of acceptor doped heterostructures, it is shown that the low energy excimer state (PLExc) transports energy anisotropically along the stacking direction of the linker chromophores, as shown in the below schematic [3]. Such directionality of the exciton motion is introduced by the structural organization of the SURMOF-2.

Surface-Anchored Metal-Organic Frameworks as Versatile Resists for Gas-Assisted E-Beam Lithography: Fabrication of Sub-10 Nanometer Structures.

We demonstrate that surface-anchored metal-organic frameworks (SURMOFs) are extraordinary well-suited as resists for high-resolution focused electron beam induced processing (FEBIP) techniques. The combination of such powerful lithographic protocols with the huge versatility of MOF materials are investigated in respect to their potential in nanostructures fabrication. The applied FEBIP methods rely on the local decomposition of Fe(CO)5 and Co(CO)3NO as precursors, either by the direct impact of the focused electron beam (electron beam induced deposition, EBID) or through the interaction of the precursor molecules with preirradiated/activated SURMOF areas (electron beam induced surface activation, EBISA). We demonstrate the huge potential of the approach for two different types of MOFs (HKUST-1 and Zn-DPDCPP). Our "surface science" approach to FEBIP, yields well-defined deposits with each investigated precursor/SURMOF combination. Local Auger electron spectroscopy reveals clean iron deposits from Fe(CO)5; deposits from Co(CO)3NO contain cobalt, nitrogen, and oxygen. EBISA experiments were successful with Fe(CO)5. Remarkably EBISA with Co(CO)3NO does not result in deposit formation on both resists, making the process chemically selective. Most importantly we demonstrate the fabrication of "nested-L" test structures with Fe(CO)5 on HKUST-1 with extremely narrow line widths of partially less than 8 nm, due to reduced electron proximity effects within the MOF-based resists. Considering that the actual diameter of the electron beam was larger than 6 nm, we see a huge potential for significant reduction of the structure sizes. In addition, the role and high potential of loading and transport of the precursor molecules within the porous SURMOF materials is discussed.

Enhancing the photoluminescence of surface anchored metal-organic frameworks: mixed linkers and efficient acceptors.

We present two approaches to enhance the photoluminescence quantum yield (PLQY) of surface-anchored metal-organic frameworks (SURMOFs). In the first approach we fabricate SURMOFs from a mix of an emissive linker with an optically-inert linker of equivalent length, diluting the emissive linker while maintaining the SURMOF structure. This approach enhances the internal PLQY. However, the increase in internal PLQY is achieved at the expense of a drastic reduction in optical absorption, thus the external PLQY remains low. To overcome this limitation, a second approach is explored wherein energy-accepting guest chromophores are infiltrated into the framework of the active linker. At the correct acceptor concentration, an internal PLQY of 52% - three times higher than the previous approach - is achieved. Additionally, the absorption remains strong leading to an external PLQY of 8%, an order of magnitude better than the previous approach. Using this strategy, we demonstrate that SURMOFs can achieve PLQYs similar to their precursor chromophores in solution. This is of relevance to SURMOFs as emitter layers in general, and we examine the optimized emitter layer as part of a photon upconversion (UC) SURMOF heterostructure. Surprisingly, the same PLQY is not observed after triplet-triplet annihilation in the UC heterostructure as after its normal photoexcitation (although the UC layers exhibit low thresholds consistent with those reported in our previous work). We discuss the potential bottlenecks in energy transport that could lead to this unexpected reduction in PLQY after excitation via triplet-triplet annihilation, and how future design of SURMOF UC multilayers could overcome these limitations.