Mesoscale Integration in Titania/J-Aggregate Hybrid Nanofibers

Porphyrin-Based Covalent Organic Frameworks: Design, Synthesis, Photoelectric Conversion Mechanism, and Applications

Photosynthesis occurs in high plants, and certain organisms show brilliant technology in converting solar light to chemical energy and producing carbohydrates from carbon dioxide (CO₂). Mimicking the mechanism of natural photosynthesis is receiving wide-ranging attention for the development of novel materials capable of photo-to-electric, photo-to-chemical, and photocatalytic transformations. Porphyrin, possessing a similar highly conjugated core ring structure to chlorophyll and flexible physical and chemical properties, has become one of the most investigated photosensitizers. Chemical modification and self-assembly of molecules as well as constructing porphyrin-based metal (covalent) organic frameworks are often used to improve its solar light utilization and electron transfer rate. Especially porphyrin-based covalent organic frameworks (COFs) in which porphyrin molecules are connected by covalent bonds combine the structural advantages of organic frameworks with light-capturing properties of porphyrins and exhibit great potential in light-responsive materials. Porphyrin-based COFs are expected to have high solar light utilization, fast charge separation/transfer performance, excellent structural stability, and novel steric selectivity by special molecular design. In this paper, we reviewed the research progress of porphyrin-based COFs in the design, synthesis, properties, and applications. We focused on the intrinsic relationship between the structure and properties, especially the photoelectric conversion properties and charge transfer mechanism of porphyrin-based COFs, and tried to provide more valuable information for the design of advanced photosensitizers. The applications of porphyrin-based COFs in photocatalysis and phototherapy were emphasized based on their special structure design and light-to-electric (or light-to-heat) conversion control.

Pre-Polymerization Enables Controllable Synthesis of Nanosheet-Based Porphyrin Polymers towards High-Performance Li-Ion Batteries

The precise regulation of nucleation growth and assembly of polymers is still an intriguing goal but an enormous challenge. In this study, we proposed a pre-polymerization strategy to regulate the assembly and growth of polymers by facilely controlling the concentration of polymerization initiator, and thus obtained two kinds of different nanosheet-based porphyrin polymer materials using tetrakis-5,10,15,20-(4-aminophenyl) porphyrin (TAPP) as the precursor. Notably, due to the π-π stacking and doping of TAPP during the preparation process, the obtained PTAPP-nanocube material exhibits a high intrinsic bulk conductivity reaching 1.49×10^-4  S m^-1 . Profiting from the large π-conjugated structure of porphyrin units, closely stacked layer structure and excellent conductivity, the resultant porphyrin polymers, as electrode materials for lithium ion batteries, deliver high specific capacity (≈650 mAh g^-1 at the current density of 100 mA g^-1 ), excellent rate performance and long-cycle stability, which are among the best reports of porphyrin polymer-based electrode materials for lithium-ion batteries, to the best of our knowledge. Therefore, such a pre-polymerization approach would provide a new insight for the controllable synthesis of polymers towards custom-made architecture and function.

Nanohybrids from nanotubular J-aggregates and transparent silica nanoshells

Organic-inorganic nanohybrids have been synthesized by in situ coating supramolecular nanotubular J-aggregates with helically wound silica ribbons, reflecting the J-aggregates' superstructure. The J-aggregates retain their morphology and optical properties in the nanohybrids, and display improved stability against elevated temperatures, chemical ambient and photo-bleaching.

Self-assembly of phosphate amphiphiles in mixtures of prebiotically plausible surfactants

The spontaneous formation of closed bilayer structures from prebiotically plausible amphiphiles is an essential requirement for the emergence of early cells on prebiotic Earth. The sources of amphiphiles could have been both endo- and exogenous (accretion of meteorite carbonaceous material or interstellar dust particles). Among all prebiotic possible amphiphile candidates, those containing phosphate are the least investigated species because their self-assembly occurs in a seemingly too narrow range of conditions. The self-assembly of simple phosphate amphiphiles should, however, be of great interest, as contemporary membranes predominantly contain phospholipids. In contrast to common expectations, we show that these amphiphiles can be easily synthesized under prebiotically plausible environmental conditions and can efficiently form bilayer structures in the presence of various co-surfactants across a large range of pH values. Vesiculation was even observed in crude reaction mixtures that contained 1-decanol as the amphiphile precursor. The two best co-surfactants promoted vesicle formation over the entire pH range in aqueous solutions. Expanding the pH range where bilayer membranes self-assemble and remain intact is a prerequisite for the emergence of early cell-like compartments and their preservation under fluctuating environmental conditions. These mixed bilayers also retained small charged solutes, such as dyes. These results demonstrate that alkyl phosphate amphiphiles might have played a significant role as early compartment building blocks.

Integrative self-assembly of functional hybrid nanoconstructs by inorganic wrapping of single biomolecules, biomolecule arrays and organic supramolecular assemblies

Synthesis of functional hybrid nanoscale objects has been a core focus of the rapidly progressing field of nanomaterials science. In particular, there has been significant interest in the integration of evolutionally optimized biological systems such as proteins, DNA, virus particles and cells with functional inorganic building blocks to construct mesoscopic architectures and nanostructured materials. However, in many cases the fragile nature of the biomolecules seriously constrains their potential applications. As a consequence, there is an on-going quest for the development of novel strategies to modulate the thermal and chemical stabilities, and performance of biomolecules under adverse conditions. This feature article highlights new methods of "inorganic molecular wrapping" of single or multiple protein molecules, individual double-stranded DNA helices, lipid bilayer vesicles and self-assembled organic dye superstructures using inorganic building blocks to produce bio-inorganic nanoconstructs with core-shell type structures. We show that spatial isolation of the functional biological nanostructures as "armour-plated" enzyme molecules or polynucleotide strands not only maintains their intact structure and biochemical properties, but also enables the fabrication of novel hybrid nanomaterials for potential applications in diverse areas of bionanotechnology.

Synthesis of chiral TiO₂ nanofibre with electron transition-based optical activity

The optical chirality induced at the absorption bands due to electronic exciton coupling of the transition dipole moments between chromophores in close proximity is ubiquitous in helical organic materials. However, inorganic materials with optical activity resulting from electronic transitions have not been explored. Here we report the synthesis of chiral TiO₂ fibres via transcription of the helical structure of amino acid-derived amphiphile fibres through coordination bonding interactions between the organics and the TiO₂ source. Upon calcination, the as-prepared amorphous TiO₂ double-helical fibres with a pitch length of ~100 nm were converted to double-helical crystalline fibres with stacks of anatase nanocrystals in an epitaxial helical relationship. Both the amorphous and anatase crystalline helical TiO₂ fibres exhibited optical response to circularly polarized light at the absorption edge around ~350 nm. This was attributed to the semiconductor TiO₂-based electronic transitions from the valence band to the conduction band under an asymmetric electric field.

Optical activity resulting from electronic transitions in chiral inorganic materials is rare. Liu et al. report the synthesis of amino acid-derived amphiphile templated chiral TiO₂ fibres, which exhibit an optical response to polarized light resulting from valence to conduction band electronic transitions.

Exciton Energy and Charge Transfer in Porphyrin Aggregate/Semiconductor (TiO2) Composites

A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications. This porphyrin aggregate enables control of energy dissipation of coherent excited states by changing the self-assembly pattern. New exciton spectral features create a new route of energy transfer in this porphyrin aggregate. The kinetic model of exciton state decay is addressed in this Perspective by reporting steady-state and transient emission and absorption studies of porphyrin J- and H-aggregates. The porphyrin J-aggregate emerges with better spectral coverage and exciton dynamics, which are suitable for light-harvesting antenna functions. This motif is explored in a photosensitization study of TiO2 semiconductor materials. The transient absorption studies show that the J-aggregate improves the photoinduced charge separation at the porphyrin/TiO2 interface. The higher charge separation is attributed to exciton-coupled charge-transfer processes in porphyrin J-aggregate/TiO2 hybrid materials. It represents the potential of porphyrin aggregates in biomimetic artificial antenna activity.