Assembly of Molecular Building Blocks into Integrated Complex Functional Molecular Systems: Structuring Matter Made to Order

Function-inspired design of molecular building blocks for their assembly into complex systems has been an objective in engineering nanostructures and materials modulation at nanoscale. This article summarizes recent research and inspiring progress in the design/synthesis of various custom-made chiral, switchable, and highly responsive molecular building blocks for the construction of diverse covalent/noncovalent assemblies with tailored topologies, properties, and functions. Illustrating the judicious selection of building blocks, orthogonal functionalities, and innate physical/chemical properties that bring diversity and complex functions once reticulated into materials, special focus is given to their assembly into porous crystalline networks such as metal/covalent–organic frameworks (MOFs/COFs), surface-mounted frameworks (SURMOFs), metal–organic cages/rings (MOCs), cross-linked polymer gels, porous organic polymers (POPs), and related architectures that find diverse applications in life science and various other functional materials. Smart and stimuli-responsive or dynamic building blocks, once embedded into materials, can be remotely modulated by external stimuli (light, electrons, chemicals, or mechanical forces) for controlling the structure and properties, thus being applicable for dynamic photochemical and mechanochemical control in constructing new forms of matter made to order. Then, an overview of current challenges, limitations, as well as future research directions and opportunities in this field, are discussed

Metal-Organic Frameworks: Photophysics, Energy Transfer, and Electronic Structure

The current landscape of technological and industrial related fields is looking for novel materials with enhanced performances, which will not only improve various fields in science, but also can ensure increased environmental safety. Recently, metal-organic frameworks (MOFs) have been shown as a promising type of material for a wide range of applications including gas storage and separation, sensing, and heterogeneous catalysis. The main advantages of MOFs rely on their modular structures as well as their porosity. For instance, the modular nature of MOFs provides a control over chromophore arrangement, systematic tuning of ligand design and synthetic conditions allowing one to systematically tune photophysical or electronic properties. Thus, these materials could be utilized as a tool to address the current need in enhancement of material performance. This work presented within the following nine chapters is focused on the design, synthesis, and characterization of MOFs that target fundamental understanding of photophysical properties, energy transfer processes, and the ability to tune electronic structures of these materials. The first chapter reviews MOF applications in areas for which development is highly dependent on fundamental studies of MOF photophysics. Next four chapters discuss a utilization of MOF as an efficient replica of a protein β- barrel to maintain chromophore emission. The major principles governing chromophore photophysical response inside a confined environment are examined. Chapters six and seven describe the key factors responsible for tunability of MOF electronic structure as a function of second metal or mixed valence sites incorporation. Chapter eight demonstrates the unprecedented role of MOF modularity necessary for engineering of radionuclide containing materials. Finally, chapter nine reveals the possibility of MOF electronic structure modulation as a function of external light stimuli. Overall, this work shows the possibility of MOF engineering towards various applications ranging from photocatalysts to optoelectronic devices

Enabling visible-light water photooxidation by coordinative incorporation of Co(II/III) cocatalytic sites into organic-inorganic hybrids: quantum chemical modeling and photoelectrochemical performance

<div><p>Coordinative incorporation of Co(II/III) cocatalytic sites into organic–inorganic hybrids of TiO₂ and “polyheptazine” (PH, poly(aminoimino)heptazine, melon, or “graphitic carbon nitride”) has been investigated both by quantum chemical calculations and experimental techniques. Specifically, density-functional theory (DFT) calculations (PBE/def2-TZVPP) suggest that Co(II/III) and Zn(II) ions adsorb in nanocavities at the surface of the hybrid PH–TiO₂ cluster, a prediction which can be further confirmed experimentally by ¹⁵N nuclear magnetic resonance in the case of the Zn complex. The absorption spectra of the complexes were characterized by time-dependent DFT calculations, suggesting a change of color upon Co ion binding which can in fact be observed with the naked eye. Hybrid TiO₂–PH photoelectrodes were impregnated with Co(II) ions from aqueous cobalt nitrate solutions. Optical absorption data suggest that Co(II) ions are predominantly present as single ions coordinated within the nitrogen cavities of TiO₂–PH, and any undesired blocking of light absorption is negligible. The cobalt-induced cocatalytic sites can efficiently couple to the holes photogenerated by visible light in TiO₂–PH, leading to complete oxidation of water to dioxygen. Our results indicate that coordinative incorporation of metal ions into well-designed surface sites in the light absorber is sufficient to drive complex multielectron transformations in artificial photosynthetic systems.</p></div