Photoinduced Isomerization of [N] in a Bimetallic Lutetium Complex.

The first lanthanide dinitrogen photoswitch [(CMeH)(THF)Lu](μ-η:η-N), , is reported. is a unique example of controlled isomerization between side-on and end-on coordination modes of [N] in a bimetallic lutetium dinitrogen complex that results in photochromism. Near-infrared light (NIR) was used to promote this effect, as evidenced by single X-ray diffraction (XRD) connectivity and Raman data, generating the [N] end-on bound isomer, [(CMeH)(THF)Lu](μ-η:η-N), .

GFP-related chromophores: photoisomerization, thermal reversion, and DNA labelling.

Due to the pronounced effect of the confined environment on the photochemical properties of 4-hydroxybenzylidene imidazolinone (HBI), a GFP-related chromophore, imidazolidinone and imidazothiazolone analogues have been studied as fluorescent probes. Their photoisomerization and their thermal reversion were studied under 365-nm-irradiation, resulting in observation of an enthalpy-entropy compensation effect. Theoretical studies were carried out to shed light on the thermal reversion mechanism.

Strong Purcell enhancement at telecom wavelengths afforded by spinel FeO nanocrystals with size-tunable plasmonic properties.

Developments in the field of nanoplasmonics have the potential to advance applications from information processing and telecommunications to light-based sensing. Traditionally, nanoscale noble metals such as gold and silver have been used to achieve the targeted enhancements in light-matter interactions that result from the presence of localized surface plasmons (LSPs). However, interest has recently shifted to intrinsically doped semiconductor nanocrystals (NCs) for their ability to display LSP resonances (LSPRs) over a much broader spectral range, including the infrared (IR).

PbS/CdS Quantum Dot Room-Temperature Single-Emitter Spectroscopy Reaches the Telecom O and S Bands via an Engineered Stability.

We synthesized PbS/CdS core/shell quantum dots (QDs) to have functional single-emitter properties for room-temperature, solid-state operation in the telecom O and S bands. Two shell-growth methods-cation exchange and successive ionic layer adsorption and reaction (SILAR)-were employed to prepare QD heterostructures with shells of 2-16 monolayers. PbS/CdS QDs were sufficiently bright and stable to resolve photoluminescence (PL) spectra representing both bands from single nanocrystals using standard detection methods, and for a QD emitting in the O-band a second-order correlation function showed strong photon antibunching, important steps toward demonstrating the utility of lead chalcogenide QDs as single-photon emitters (SPEs).

Growth of Crystalline Bimetallic Metal-Organic Framework Films via Transmetalation.

Crystalline films of the Cu(BTC) (BTC = 1,3,5-benzenetricarboxylate) metal-organic framework (MOF) have been grown by dip-coating an alumina/Si(111) substrate in solutions of Cu(II) acetate and the organic linker HBTC. Atomic force microscopy (AFM) experiments demonstrate that the substrate is completely covered by the MOF film, while grazing incidence wide-angle X-ray scattering (GIWAXS) establishes the crystallinity of the films. Forty cycles of dip-coating results in a film that is ∼70 nm thick with a root mean squared roughness of 25 nm and crystallites ranging from 50-160 nm in height.

Confinement-Driven Photophysics in Cages, Covalent-Organic Frameworks, Metal-Organic Frameworks, and DNA.

Photophysics tunability through alteration of framework aperture (metal-organic framework (MOF) = variable; guest = constant) was probed for the first time in comparison with previously explored concepts (MOF = constant; guest = variable). In particular, analysis of the confinement effect on a photophysical response of integrated 5-(3-chlorobenzylidene)-2,3-dimethyl-3,5-dihydro-4-imidazol-4-one (Cl-BI) chromophore allowed us to establish a photophysics-aperture relationship. To shed light on the observed correlation, the framework confined environment was replicated using a molecular cage, Pd(TPT) (TPT = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine), thus allowing for utilization of crystallography, spectroscopy, and theoretical simulations to reveal the effect a confined space has on the chromophore's molecular conformation (including disruption of strong hydrogen bonding and novel conformer formation) and any associated changes on a photophysical response.

Thermodynamics and Electronic Properties of Heterometallic Multinuclear Actinide-Containing Metal-Organic Frameworks with "Structural Memory".

Thermodynamic studies of actinide-containing metal-organic frameworks (An-MOFs), reported herein for the first time, are a step toward addressing challenges related to effective nuclear waste administration. In addition to An-MOF thermochemistry, enthalpies of formation were determined for the organic linkers, 2,2'-dimethylbiphenyl-4,4'-dicarboxylic acid (HMeBPDC) and biphenyl-4,4'-dicarboxylic acid (HBPDC), which are commonly used building blocks for MOF preparation. The electronic structure of the first example of An-MOF with mixed-metal AnAn'-nodes was influenced through coordination of transition metals as shown by the density of states near the Fermi edge, changes in the Tauc plot, conductivity measurements, and theoretical calculations.

"Boarding-Up": Radiation Damage and Radionuclide Leaching Kinetics in Linker-Capped Metal-Organic Frameworks.

For the first time, we report the ability to control radionuclide species release kinetics in metal-organic frameworks (MOFs) as a function of postsynthetic capping linker installation, which is essential for understanding MOF potential as viable radionuclide wasteform materials or versatile platforms for sensing, leaching, and radionuclide sequestration. The radiation damage of prepared frameworks under γ radiation has also been studied. We envision that the presented studies are the first steps toward utilization of the reported scaffolds for more efficient nuclear waste administration.

Connecting Wires: Photoinduced Electronic Structure Modulation in Metal-Organic Frameworks.

Electronic structure modulation of metal-organic frameworks (MOFs) through the connection of linker "wires" as a function of an external stimulus is reported for the first time. The established correlation between MOF electronic properties and photoisomerization kinetics as well as changes in an absorption profile is unprecedented for extended well-defined structures containing coordinatively integrated photoresponsive linkers. The presented studies were carried out on both single crystal and bulk powder with preservation of framework integrity.

Inkjet-Printed Photoluminescent Patterns of Aggregation-Induced-Emission Chromophores on Surface-Anchored Metal-Organic Frameworks.

Organic chromophores that exhibit aggregation-induced emission (AIE) are of interest for applications in displays, lighting, and sensing, because they can maintain efficient emission at high molecular concentrations in the solid state. Such advantages over conventional chromophores could allow thinner conversion layers of AIE chromophores to be realized, with benefits in terms of the efficiency of the optical outcoupling, thermal management, and response times. However, it is difficult to create large-area optical quality thin films of efficiently performing AIE chromophores.

Stack the Bowls: Tailoring the Electronic Structure of Corannulene-Integrated Crystalline Materials.

We report the first examples of purely organic donor-acceptor materials with integrated π-bowls (πBs) that combine not only crystallinity and high surface areas but also exhibit tunable electronic properties, resulting in a four-orders-of-magnitude conductivity enhancement in comparison with the parent framework. In addition to the first report of alkyne-azide cycloaddition utilized for corannulene immobilization in the solid state, we also probed the charge transfer rate within the Marcus theory as a function of mutual πB orientation for the first time, as well as shed light on the density of states near the Fermi edge. These studies could foreshadow new avenues for πB utilization for the development of optoelectronic devices or a route for highly efficient porous electrodes.

Flipping the Switch: Fast Photoisomerization in a Confined Environment.

Stimuli-responsive materials are vital for addressing emerging demands in the advanced technology sector as well as current industrial challenges. Here, we report for the first time that coordinative integration of photoresponsive building blocks possessing photochromic spiropyran and diarylethene moieties within a rigid scaffold of metal-organic frameworks (MOFs) could control photophysics, in particular, cycloreversion kinetics, with a level of control that is not accessible in the solid state or solution. On the series of photoactive materials, we demonstrated for the first time that photoisomerization rates of photochromic compounds could be tuned within almost 2 orders of magnitude.

Photochemistry and photophysics of MOFs: steps towards MOF-based sensing enhancements.

In this review, we highlight how recent advances achieved in the fields of photochemistry and photophysics of metal-organic frameworks (MOFs) could be applied towards the engineering of next generation MOF-based sensing devices. In addition to high surface area and structural tunability, which are crucial for efficient sensor development, progress in the field of MOF-based sensors could rely on the combination of MOF light-harvesting ability, understanding energy transfer processes within a framework, and application of MOF-based photocatalysis towards sensing enhancement. All photophysical concepts could be integrated within one material to improve efficiency and selectivity of sensing devices.

Actinide-based MOFs: a middle ground in solution and solid-state structural motifs.

In this review, we highlight how recent advances in the field of actinide structural chemistry of metal-organic frameworks (MOFs) could be utilized towards investigations relative to efficient nuclear waste administration, driven by the interest towards development of novel actinide-containing architectures as well as concerns regarding environmental pollution and nuclear waste storage. We attempt to perform a comprehensive analysis of more than 100 crystal structures of the existing An (U,Th)-based MOFs to establish a correlation between structural density and wt% of actinide and bridge structural motifs common for natural minerals with ones typically observed in the solution chemistry of actinides. In addition to structural considerations, we showcase the benefits of MOF modularity and porosity towards the stepwise building of hierarchical material complexity and the capture of nuclear fission products, such as technetium and iodine.

Multifaceted Modularity: A Key for Stepwise Building of Hierarchical Complexity in Actinide Metal-Organic Frameworks.

Growing necessity for efficient nuclear waste management is a driving force for development of alternative architectures toward fundamental understanding of mechanisms involved in actinide (An) integration inside extended structures. In this manuscript, metal-organic frameworks (MOFs) were investigated as a model system for engineering radionuclide containing materials through utilization of unprecedented MOF modularity, which cannot be replicated in any other type of materials. Through the implementation of recent synthetic advances in the MOF field, hierarchical complexity of An-materials was built stepwise, which was only feasible due to preparation of the first examples of actinide-based frameworks with "unsaturated" metal nodes.

A metal-organic framework as a flask: photophysics of confined chromophores with a benzylidene imidazolinone core.

Photophysics and dynamics of chromophores with a benzylidene imidazolinone core, responsible for emission of green fluorescent protein variants, were studied as a function of host topology by three approaches. Coordinative, non-coordinative, and "fastened" immobilization were utilized to study chromophore emission. Variable-temperature quadrupolar spin-echo H NMR spectra are reported.

Hierarchical Corannulene-Based Materials: Energy Transfer and Solid-State Photophysics.

We report the first example of a donor-acceptor corannulene-containing hybrid material with rapid ligand-to-ligand energy transfer (ET). Additionally, we provide the first time-resolved photoluminescence (PL) data for any corannulene-based compounds in the solid state. Comprehensive analysis of PL data in combination with theoretical calculations of donor-acceptor exciton coupling was employed to estimate ET rate and efficiency in the prepared material.

Electronic Properties of Bimetallic Metal-Organic Frameworks (MOFs): Tailoring the Density of Electronic States through MOF Modularity.

The development of porous well-defined hybrid materials (e.g., metal-organic frameworks or MOFs) will add a new dimension to a wide number of applications ranging from supercapacitors and electrodes to "smart" membranes and thermoelectrics.

Photophysics, Dynamics, and Energy Transfer in Rigid Mimics of GFP-based Systems.

Engineering of novel systems capable of efficient energy capture and transfer in a predesigned pathway could potentially boost applications varying from organic photovoltaics to catalytic platforms and have implications for energy sustainability and green chemistry. While light-harvesting properties of different materials have been studied for decades, recently, there has been great progress in the understanding and modeling of short- and long-range energy transfer processes through utilization of metal-organic frameworks (MOFs). In this Forum Article, the recent advances in efficient multiple-chromophore coupling in well-defined metal-organic materials through mimicking a protein system possessing near 100% energy transfer are discussed.

Fulleretic Well-Defined Scaffolds: Donor-Fullerene Alignment Through Metal Coordination and Its Effect on Photophysics.

Herein, we report the first example of a crystalline metal-donor-fullerene framework, in which control of the donor-fullerene mutual orientation was achieved through chemical bond formation, in particular, by metal coordination. The (13) C cross-polarization magic-angle spinning NMR spectroscopy, X-ray diffraction, and time-resolved fluorescence spectroscopy were performed for comprehensive structural analysis and energy-transfer (ET) studies of the fulleretic donor-acceptor scaffold. Furthermore, in combination with photoluminescence measurements, the theoretical calculations of the spectral overlap function, Förster radius, excitation energies, and band structure were employed to elucidate the photophysical and ET processes in the prepared fulleretic material.

Redox-Active Corannulene Buckybowls in a Crystalline Hybrid Scaffold.

A porous crystalline corannulene-containing scaffold, which combines the periodicity, dimensionality, and structural modularity of hybrid frameworks with the intrinsic properties of redox-active π-bowls, has been prepared. Single-crystal and powder X-ray diffraction, ab initio density functional theory computations, gas sorption analysis, fluorescence spectroscopy, and cyclic voltammetry were employed to study the properties of the novel corannulene derivatives and the buckybowl-based hybrid materials. X-ray diffraction studies revealed the preservation of the corannulene bowl inside the prepared rigid matrix, which offers the unique opportunity to extend the scaffold dimensionality through the buckybowl curvature.

A Bio-inspired Approach for Chromophore Communication: Ligand-to-Ligand and Host-to-Guest Energy Transfer in Hybrid Crystalline Scaffolds.

Efficient multiple-chromophore coupling in a crystalline metal-organic scaffold was achieved by mimicking a protein system possessing 100% energy-transfer (ET) efficiency between a green fluorescent protein variant and cytochrome b562. The two approaches developed for ET relied on the construction of coordination assemblies and host-guest coupling. Based on time-resolved photoluminescence measurements in combination with calculations of the spectral overlap function and Förster radius, we demonstrated that both approaches resulted in a very high ET efficiency.

Mimic of the green fluorescent protein β-barrel: photophysics and dynamics of confined chromophores defined by a rigid porous scaffold.

Chromophores with a benzylidene imidazolidinone core define the emission profile of commonly used biomarkers such as the green fluorescent protein (GFP) and its analogues. In this communication, artificially engineered porous scaffolds have been shown to mimic the protein β-barrel structure, maintaining green fluorescence response and conformational rigidity of GFP-like chromophores. In particular, we demonstrated that the emission maximum in our artificial scaffolds is similar to those observed in the spectra of the natural GFP-based systems.