A Photoactive Porphyrin-Based Periodic Mesoporous Organosilica Thin Film

Incorporation of ultrafine TiO2/CdS heterojunction in dendritic porphyrins mesoporous silica nanospheres for efficient photocatalytic oxidation of styrene

In this paper, a novel host-guest assembly strategy is developed to incorporate TiO2 nanoparticles and CdS quantum dots (CdS QDs) into the photoactive dendritic porphyrins mesoporous silica nanospheres (DPMSN) channels for establishing heterojunctions nanoreactors (designated as DPMSTNC). The well-defined dendritic architecture facilitates the high dispersion of TiO2/CdS heterojunctions within the DPMSN matrix, effectively maximizing the interfacial contact area between the heterojunction components and the cobalt porphyrin framework. Crucially, the synergistic interplay of cobalt porphyrins incorporated in the silica framework and the ultra-small TiO2/CdS heterojunction in the dendritic channels promotes efficient charge transfer and separation in the nanoreactor. The optimized DPMSTNC nanoreactor exhibits excellent catalytic performance with a conversion of 96.0 % and a selectivity of 92.0 % in styrene oxidation, which significantly surpasses that of single-component catalysts and simple composite heterostructure catalysts. This nanoreactor design strategy, which combines spatially confined heterojunctions with photoactive porous frameworks, provides a novel and versatile platform for developing high-efficiency photocatalytic systems through precise nanoarchitectural control.

Large-Area Ultrathin Covalent-Organic Framework Membranes for Surface-Enhanced Raman Scattering: Optimal Performance Through Thickness Control

Exploration and construction of novel π-conjugated organic semiconductors with low cost, small background interference, and excellent performance as surface-enhanced Raman scattering (SERS) substrates is one of the current focuses for the development of SERS technology. Based on precise control over synthesis conditions, a series of large-area tetraphenylporphyrin-based 2D covalent-organic framework membranes (2D-porphyrin-COFs) with high uniformity and precisely controllable thickness are constructed as SERS substrates. The delicate balance among the intensity of the substrate interference, the degree of π-conjugation extension, and the proportion of the edge-on channels within the total exposed region results in the optimal SERS performance of ultrathin multilayer 2D-porphyrin-COFs with the thickness between 5.0 to 9.0 nm toward MB, including the enhancement factor on the order of 105 and the experimental limit of detection down to 10-8 M, which are comparable to classic plasmonic metal substrates. This work highlights the powerful application potential of COFs in the SERS field and unveils thickness control as an effective strategy to facilitate the exploration of high-performance organic SERS substrates.

Facile Fabrication of Monodisperse Vinyl Hybrid Core-Shell Silica Microsphere with Short Range Radial Channel in bi-phase System

The development of monodisperse hybrid silica microspheres with highly regular pore structure and uniform distribution of functional groups have significant value in the biomolecular separation field. In this work, the short range ordered pore channels are precisely constructed onto the non-porous silica microsphere surface by a bi-phase assembly method, and the cylindrical silica channel introduced a plethora of vinyl groups by "one-pot" co-condensation to form vinyl hybrid silica shell. As hydrophilic interaction chromatography (HILIC) stationary phase, the vinyl hybrid core-shell silica microsphere is simply modified with zwitterion glutathione (SiO2@SiO2-GSH), in which the HILIC enrichment process is significantly shortened due to its specific porous characteristics. Most importantly, SiO2@SiO2-GSH microsphere can enrich 2186 N-glycopeptides from the rat liver protein digest within 2 min, which mapped to 806 glycoproteins. Compared with HILIC enrichment result within 1 h, the glycoproteins and glycopeptides overlap are 88.3% and 79.1%, performing excellent reproducibility. The short range ordered channels onto the silica microsphere surface exhibit excellent mass transfer efficiency, so the developed bi-phase assembly method is expected to design more advanced hybrid silica materials for other urgently fields.

Electrocatalytic oxidation of pyrrole on a quasi-reversible silver nanodumbbell particle surface for supramolecular porphyrin production

Photoactive supramolecular porphyrin assemblies are attractive molecules for light-harvesting applications. This is due to their relatively non-toxicity, biological activities and charge and energy exchange characteristics. However, the extreme cost associated with their synthesis and requirements for toxic organic solvents during purification pose a challenge to the sustainability characteristics of their applications. This work presents the first report on the sustainable synthesis, spectroscopic and photophysical characterizations of a near-infrared (NIR) absorbing Ca(II)-meso-tetrakis (4-hydroxyphenyl)porphyrin using an electrolyzed pyrrole solution. The latter was obtained by cycling the pyrrole solution across the silver nanodumbbell particle surface at room temperature. The electrolyzed solution condensed readily with acidified p-hydroxybenzaldehyde, producing the targeted purple porphyrin. The non-electrolyzed pyrrole solution formed a green substance with significantly different optical properties. Remarkable differences were observed in the voltammograms of the silver nanodumbbell particles and those of the conventional gold electrode during the pyrrole cycling, suggesting different routes of porphyrin formation. The rationale behind these formations and the associated mechanisms were extensively discussed. Metalation with aqueous Ca2+ ion caused a Stokes shift of 38.75 eV. The current study shows the advantage of the electrochemical method towards obtaining sustainable light-harvesting porphyrin at room temperature without the need for high-energy-dependent conventional processes.

A Redox-active Microporous Organosiloxane Containing a Stable Neutral Radical, Trioxotriangulene

A new silyl-substituted trioxotriangulene ( TOT ) neutral radical and corresponding porous organosiloxanes (POSs) were synthesized. The neutral radical exhibited a peculiarly high stability and formed a diamagnetic π-dimer characteristic to TOT neutral radicals stabilized by the strong multiple SOMO-SOMO interaction in both solution and solid states. POSs including TOT units within the organosiloxane-wall were prepared by polycondensation of the silyl groups, and formed microporous structures with ~1 nm-size diameters. Redox ability of TOT units in the POS was demonstrated by the treatment of oxidant/reductant in heterogeneous suspension condition, where the TOT units were reversibly converted between reduced and neutral radical species. Furthermore, the solid-state electrochemical measurements of the POS revealed the reversible multi-stage redox ability of TOT units involving polyanionic species within the organosiloxane-wall.

Conductive Thin Films over Large Areas by Supramolecular Self-Assembly

We report a "one-step" method for preparing conductive thin films with cylindrical microdomains oriented normal to the surface over large areas using the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS₁₉-b-P4VP₅) and 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (HOTPP). HOTPP interacts with the P4VP block by hydrogen bonding between the hydroxyl group of HOTPP and pyridine ring of PS₁₉-b-P4VP₅, forming cylindrical P4VP(HOTPP) domains having an average diameter of ∼17 nm in a PS matrix. Dynamic light scattering, contact angle, and in situ grazing incidence small-angle X-ray scattering measurements show a morphological transition from spherical micelles in solution to cylindrical microdomains oriented normal to the substrate surface during the drying process. From the dependence of current on voltage, an average current of ∼4.0 nA is found to pass through a single microdomain, pointing to a promising route for organic semiconductor device applications.

Highly Active Ruthenium Catalyst Supported on Magnetically Separable Mesoporous Organosilica Nanoparticles

A facile and direct method for synthesizing magnetic periodic mesoporous organosilica nanoparticles from pure organosilane precursors is described. Magnetic ethylene- and phenylene-bridged periodic mesoporous organosilica nanoparticles (PMO NPs) were prepared by nanoemulsification techniques. For fabricating magnetic ethylene- or phenylene-bridged PMO NPs, hydrophobic magnetic nanoparticles in an oil-in-water (o/w) emulsion were prepared, followed by a sol–gel condensation of the incorporated bridged organosilane precursor (1,2 bis(triethoxysilyl)ethane or 1,4 bis(triethoxysilyl)benzene), respectively. The resulting materials were characterized using high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (XRD), solid-state NMR analysis, and nitrogen sorption analysis (N2-BET). The magnetic ethylene-bridged PMO NPs were successfully loaded using a ruthenium oxide catalyst by means of sonication and evaporation under mild conditions. The obtained catalytic system, termed Ru@M-Ethylene-PMO NPS, was applied in a reduction reaction of aromatic compounds. It exhibited very high catalytic behavior with easy separation from the reaction medium by applying an external magnetic field.

Enforcing Extended Porphyrin J-Aggregate Stacking in Covalent Organic Frameworks

The potential of covalent organic frameworks (COFs) for realizing porous, crystalline networks with tailored combinations of functional building blocks has attracted considerable scientific interest in the fields of gas storage, photocatalysis, and optoelectronics. Porphyrins are widely studied in biology and chemistry and constitute promising building blocks in the field of electroactive materials, but they reveal challenges regarding crystalline packing when introduced into COF structures due to their nonplanar configuration and strong electrostatic interactions between the heterocyclic porphyrin centers. A series of porphyrin-containing imine-linked COFs with linear bridges derived from terephthalaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, 4,4'-biphenyldicarboxaldehyde and thieno[3,2- b]thiophene-2,5-dicarboxaldehyde, were synthesized, and their structural and optical properties were examined. By combining X-ray diffraction analysis with density-functional theory (DFT) calculations on multiple length scales, we were able to elucidate the crystal structure of the newly synthesized porphyrin-based COF containing thieno[3,2- b]thiophene-2,5-dicarboxaldehyde as linear bridge. Upon COF crystallization, the porphyrin nodes lose their 4-fold rotational symmetry, leading to the formation of extended slipped J-aggregate stacks. Steady-state and time-resolved optical spectroscopy techniques confirm the realization of the first porphyrin J-aggregates on a > 50 nm length scale with strongly red-shifted Q-bands and increased absorption strength. Using the COF as a structural template, we were thus able to force the porphyrins into a covalently embedded J-aggregate arrangement. This approach could be transferred to other chromophores; hence, these COFs are promising model systems for applications in photocatalysis and solar light harvesting, as well as for potential applications in medicine and biology.

Facile one-pot synthesis of a porphyrin-based hydrophilic porous organic polymer and application as recyclable absorbent for selective separation of methylene blue

With the development of dye production and printing industry, dyes wastewater has increased dramatically. The resulting environmental pollution problem is increasing seriously. In the present work, a porphyrin-based porous organic polymer (PPOPs-OH) was synthesized by using pyrrole and 2,6-dihydroxynaphthalene-1,5-dicarbaldehyde (DHNDA) as basic building block in situ. This method was cost- and time-efficient, without the participation of metal catalysts. Further reaction of PPOPs-OH with chlorosulfonic acid, a new sulfonic acid functional material (PPOPs-SO₃H) was obtained with the increasing electronegativity and hydrophilicity. PPOPs-SO₃H exhibit good adsorption capacity for methylene blue (MB) from water (980.4 mg g^-1) and excellent selectivity for MB in the present of rhodamine B (RhB) and methyl orange (MO). Mechanism investigation revealed that electrostatic in comparison with π-π interaction is the prominent force in the absorption process. Recycling experiments found the absorption properties of PPOPs-SO₃H did not reduce significantly after several cycles. As a consequence, our findings highlight an appealing opportunities for covalent organic polymers with their potential application as high-efficiency and robust adsorbents for pollutants removal and environmental protection.

Synthesis and Optical Applications of Periodic Mesoporous Organosilicas

Periodic mesoporous organosilicas (PMOs), synthesized via surfactant-directed self-assembly of a polysilylated organic precursor (R[Si(OR')₃]_n; n≥2, R: organic group), are promising candidates such as catalysts and adsorbents, and for use in optical and electrical devices, owing to their high surface area, well-defined nanoporous structure, and highly functional organosilica framework. Their framework functionality can be widely tuned by selecting appropriate organic groups and controlling their arrangement. This chapter describes the synthesis and structure of PMOs with simple organic groups such as ethane and benzene, and the unique properties and optical applications of functional PMOs. Special light-harvesting properties and their exploitation in photocatalysis, highly emissive PMOs and their application to color-tunable transparent films, hole-transporting PMOs and their use in organic solar cells, and PMOs containing chelating ligands and their use as solid supports for heterogeneous metal complex catalysis are described.

Charge Separation in a Multifunctionalized Framework of Hydrogen-Bonded Periodic Mesoporous Organosilica

Integration of functional molecular parts into nanoporous materials in a state that allows intermolecular charge or energy transfer is one of the key approaches to the development of photofunctional and electroactive materials. Herein, we report charge separation in a functionalized framework of a periodic mesoporous organosilica (PMO) self-assembled by hydrogen bonds. Electroactive π-conjugated organic species with different electron-donating and electron-accepting properties were selectively fixed onto the external surface of a nanoparticulate PMO, within the pore wall, and onto the surface of the internal mesopore. UV irradiation of the modified PMO resulted in photoinduced electron transfer and charge separation from the external surface to the pore wall and from the pore wall to the surface of the internal mesopores. These results suggest the high potential of multifunctionalized PMOs in the construction of photocatalytic reaction fields.

Wisely Designed Phthalocyanine Derivative for Convenient Molecular Fabrication on a Substrate

An axial-substituted silicon phthalocyanine derivative, SiPc(OR)₂ (R = C₄H₉), that is soluble in organic solvent is conveniently synthesized. This silicon phthalocyanine derivative reacts with a hydroxyl group on a substrate and then with another phthalocyanine derivative under mild conditions. The accumulation number of the phthalocyanine molecules on the substrates is easily controlled by the immersion time. On the basis of AFM (atomic force microscopy) images, the surface of the phthalocyanine-modified glass substrate has uneven structures on the nanometer scale. ITO electrodes modified with the composition of the phthalocyanine derivative and PCBM show stable cathodic photocurrent generation upon light irradiation.

Spectrally Switchable Photodetection with Near-Infrared-Absorbing Covalent Organic Frameworks

Most covalent organic frameworks (COFs) to date are made from relatively small aromatic subunits, which can only absorb the high-energy part of the visible spectrum. We have developed near-infrared-absorbing low bandgap COFs by incorporating donor–acceptor-type isoindigo- and thienoisoindigo-based building blocks. The new materials are intensely colored solids with a high degree of long-range order and a pseudo-quadratic pore geometry. Growing the COF as a vertically oriented thin film allows for the construction of an ordered interdigitated heterojunction through infiltration with a complementary semiconductor. Applying a thienoisoindigo-COF:fullerene heterojunction as the photoactive component, we realized the first COF-based UV- to NIR-responsive photodetector. We found that the spectral response of the device is reversibly switchable between blue- and red-sensitive, and green- and NIR-responsive. To the best of our knowledge, this is the first time that such nearly complete inversion of spectral sensitivity of a photodetector has been achieved. This effect could lead to potential applications in information technology or spectral imaging.

A facile template route to periodic mesoporous organosilicas nanospheres with tubular structure by using compressed CO2

Periodic mesoporous organosilicas (PMOs) nanospheres with tubular structure were prepared with compressed CO₂ using cationic and anionic mixed surfactant (CTAB/SDS) and triblock copolymer Pluronic P123 as bi-templates. TEM, N₂ adsorption-desorption, solid NMR, and FTIR were employed to characterize the obtained materials. Compressed CO₂ severed as acidic reagent to promote the hydrolysis of organosilicas, and could tune the morphology and structure of the obtained PMOs nanomaterials simple by adjusting the CO₂ pressure during the synthesis process. Rhodamine B (RB) and Ibuprofen (IBU), as the model dye and drug, were loaded into the prepared nanomaterials to reveal its adsorption and desorption ability. Furthermore, different molars of the surfactant (CTAB/SDS) and organosilane precursor (BTEB) were investigated to show the effect of the surfactant concentration on the morphology and structure of the PMOs prepared with compressed CO₂, and some different structures were obtained. A possible mechanism for the synthesis of PMOs with tubular structure using compressed CO₂ was proposed based on the experimental results.

Diacetylene-Bridged Periodic Mesoporous Organosilicas with Aggregates: Synthesis and Charge/Energy-Transfer Properties

Diacetylene-bridged periodic mesoporous organosilicas (DAPMOs) with aggregates were synthesized and characterized. The DAPMO-based donor-acceptor charge-transfer (CT) system was prepared under ambient conditions, in which the diacetylenic groups in the pore walls were the electron donors and the decylviologen molecules acted as electron acceptors in the pore channels. The UV/Vis diffuse reflectance spectra and soft X-ray absorption near-edge structure (XANES) spectroscopy showed the formation of the CT complex. Importantly, energy transfer from the diacetylene aggregates to the CT complex occurred upon excitation at 330 nm, which was demonstrated by the fluorescence spectra of the CT systems. This design of hybrid organic-inorganic materials based on PMOs is promising to construct effective electron and energy transfer systems to fabricate optoelectronic materials.

Syntheses and applications of periodic mesoporous organosilica nanoparticles

Periodic Mesoporous Organosilica (PMO) nanomaterials are envisioned to be one of the most prolific subjects of research in the next decade. Similar to mesoporous silica nanoparticles (MSN), PMO nanoparticles (NPs) prepared from organo-bridged alkoxysilanes have tunable mesopores that could be utilized for many applications such as gas and molecule adsorption, catalysis, drug and gene delivery, electronics, and sensing; but unlike MSN, the diversity in chemical nature of the pore walls of such nanomaterials is theoretically unlimited. Thus, we expect that PMO NPs will attract considerable interest over the next decade. In this review, we will present a comprehensive overview of the synthetic strategies for the preparation of nanoscaled PMO materials, and then describe their applications in catalysis and nanomedicine. The remarkable assets of the PMO structure are also detailed, and insights are provided for the preparation of more complex PMO nanoplatforms.

Potential Tuning of Nanoarchitectures Based on Phthalocyanine Nanopillars: Construction of Effective Photocurrent Generation Systems

Nanopillars composed of a photoresponsive phthalocyanine derivative have been conveniently fabricated using a continuous silane coupling reaction on a substrate. The chemical potentials of phthalocyanine nanopillars (PNs) are precisely controlled by changing the number of phthalocyanine derivatives on the substrate. In addition, photocurrent generation efficiencies have been strongly influenced by the number of phthalocyanine derivatives. High photocurrent conversion cells in a solid state have been obtained by the combination of PNs and a fullerene derivative.

Coupling of chromophores with exactly opposite luminescence behaviours in mesostructured organosilicas for high-efficiency multicolour emission

Aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) materials are important for various fluorescence-based applications but cannot easily collaborate because of their opposite luminescence behaviours. Here, we demonstrate a strategy to integrate AIE and ACQ chromophores in periodic mesoporous organosilicas (PMOs) for high-efficiency multicolour emission. Tetraphenylethene (TPE)-bridged AIE-PMOs are prepared as hosts to encapsulate ACQ dyes (e.g. RhB), which enables fine-tuning of ACQ@AIE-PMO emissions over the entire visible spectrum in the solid and film states. Significantly, high-quality white light is achieved with CIE coordinates of (0.32, 0.33) and a quantum yield of up to 49.6%. Because of their high stability and solution processability, the ACQ@AIE-PMOs can be applied in solid-state lighting and bioimaging. This design concept opens up new perspectives for developing high-performance luminescent materials by the combination of a wide variety of AIE and ACQ chromophores.

Self-directedly assembled porphyrin thin films with high photoactivity

A highly photoactive porphyrin thin films were self-directedly assembled by using 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin cobalt and γ-isocyanatopropyltriethoxysilane as the reactants.

Extraction of photogenerated electrons and holes from a covalent organic framework integrated heterojunction

Covalent organic frameworks (COFs) offer a strategy to position molecular semiconductors within a rigid network in a highly controlled and predictable manner. The π-stacked columns of layered two-dimensional COFs enable electronic interactions between the COF sheets, thereby providing a path for exciton and charge carrier migration. Frameworks comprising two electronically separated subunits can form highly defined interdigitated donor-acceptor heterojunctions, which can drive the photogeneration of free charge carriers. Here we report the first example of a photovoltaic device that utilizes exclusively a crystalline organic framework with an inherent type II heterojunction as the active layer. The newly developed triphenylene-porphyrin COF was grown as an oriented thin film with the donor and acceptor units forming one-dimensional stacks that extend along the substrate normal, thus providing an optimal geometry for charge carrier transport. As a result of the degree of morphological precision that can be achieved with COFs and the enormous diversity of functional molecular building blocks that can be used to construct the frameworks, these materials show great potential as model systems for organic heterojunctions and might ultimately provide an alternative to the current disordered bulk heterojunctions.