Aluminum Porphyrin Research Articles

Two in one: aluminum porphyrin-based porous organic polymers containing symmetrical quaternary phosphonium salts for catalytic conversion of CO2 into cyclic carbonates.

Based on the double activation models of epoxides, the design and synthesis of ionic porous organic polymers (iPOPs) is considered to be very attractive and promising but has remained a great challenge in recent decades owing to electrostatic interactions between charged groups. In this contribution, we developed a two-in-one strategy to fabricate metalloporphyrin-based iPOPs with unique nanostructures (named AlPor-QP@POP), which are composed of aluminum porphyrin units and three-dimensional quaternary phosphonium salts that work synergistically in the cycloaddition of CO2 with epoxides under mild conditions. The high symmetry of two monomers allows them to possess similar reactivity ratios and thus endows AlPor-QP@POP with densely located active sites, a large surface area and good CO2 capture capacity. More importantly, bifunctional AlPor-QP@POP has enormous potential to produce cyclic carbonates with simulated flue gas under ambient conditions. Moreover, AlPor-QP@POP can be readily recycled and efficiently reused more than ten times without an obvious decrease in catalytic activity. Finally, kinetic investigations and a comparative study have been conducted to understand the possible mechanism of CO2 catalytic cycloaddition.

Polymeric catalyst with polymerization-enhanced Lewis acidity for CO2-based copolymers

Ring-opening copolymerization of CO2 and epoxides is a promising way to manufacture high value-added materials. Despite a variety of catalyst systems have been reported, the reaction is still limited by low activity and polymer selectivity. Herein, a strategy of polymerization-enhanced Lewis acidity is reported to construct a series of highly efficient polymeric aluminum porphyrin catalysts (PAPCs). The characterization of the coordination equilibrium constant (Keq) showed significantly enhanced Lewis acidity of PAPC (Keq = 18.2 L/mol) compared to the monomeric counterpart (Keq = 6.4 L/mol), accompanied with increased turnover frequency (TOF) from 136 h−1 to 5500 h−1. Through detailed regulation of Lewis acidity, the highly Lewis acidic PAPC-OTs displayed a record high TOF of 30,200 h−1 with polymer selectivity of up to 99%.

Supported Catalyst Enables Synthesis of Colorless CO2-Polyols with Ultra-Low Molecular Weight.

Ultra-low molecular weight (ULMW) CO2-polyols with well-defined hydroxyl end groups represent useful soft segments for the preparation of high-performance polyurethane foams. However, owing to the poor proton tolerance of catalysts towards CO2/epoxide telomerization, it remains challenging to synthesize ULMW yet colorless CO2-polyols. Herein, we propose an immobilization strategy of constructing supported catalysts by chemical anchoring of aluminum porphyrin on Merrifield resin. The resulting supported catalyst displays both extremely high proton tolerance (~8000 times than equivalent of metal center) and independence of cocatalyst, affording CO2-polyols with ULMW (580 g mol-1) and high polymer selectivity (> 99%). Moreover, the ULMW CO2-polyols with various architectures (tri-, quadra-, and hexa-arm) can be obtained, suggesting the wide proton universality of supported catalysts. Notably, benefiting from the heterogeneous nature of the supported catalyst, colorless products can be facilely achieved by simple filtration. The present strategy provides a platform for the synthesis of colorless ULMW polyols derived from not only CO2/epoxides, but also lactone, anhydrides et al. or their combinations.

A Supported Catalyst that Enables the Synthesis of Colorless CO2‐Polyols with Ultra‐Low Molecular Weight

AbstractUltra‐low molecular weight (ULMW) CO2‐polyols with well‐defined hydroxyl end groups represent useful soft segments for the preparation of high‐performance polyurethane foams. However, owing to the poor proton tolerance of catalysts towards CO2/epoxide telomerization, it remains challenging to synthesize ULMW yet colorless CO2‐polyols. Herein, we propose an immobilization strategy of constructing supported catalysts by chemical anchoring of aluminum porphyrin on Merrifield resin. The resulting supported catalyst displays both extremely high proton tolerance (≈8000 times the equivalents of metal centers) and independence of cocatalyst, affording CO2‐polyols with ULMW (580 g mol−1) and high polymer selectivity (>99 %). Moreover, the ULMW CO2‐polyols with various architectures (tri‐, quadra‐, and hexa‐arm) can be obtained, suggesting the wide proton universality of supported catalysts. Notably, benefiting from the heterogeneous nature of the supported catalyst, colorless products can be facilely achieved by simple filtration. The present strategy provides a platform for the synthesis of colorless ULMW polyols derived from not only CO2/epoxides, but also lactone, anhydrides etc. or their combinations.

Ultrafast electron injection in TiO2 surface-anchored aluminum(III) porphyrin stacks

Two surface-anchored aluminum(III) porphyrin (AlPorF[Formula: see text] stacks, AlPorF3(Py)-COO/TiO2 and AlPorF3(Ph)-COO/TiO2, have been constructed to investigate the interfacial electron injection from the AlPorF3 into the conduction band of the TiO2 nanoparticles as a function of stacking topology. The Lewis acid properties of AlPorF3 were combined with the electronic and surface properties of TiO2 to obtain the investigated porphyrin stacks. The axial Lewis base, pyridyl (Py) unit, in AlPorF3(Py)-COO/TiO2 directs the porphyrins to stack on the TiO2 surface in a layered fashion. The absence of a Lewis base in AlPorF3(Ph)-COO/TiO2 is unable to form such defined stacks. The AlPorF3(Py)-COO/TiO2 and AlPorF3(Ph)-COO/TiO2 were characterized by steady-state and transient spectroscopic techniques. Transient absorption spectral studies show that surface-stacked hybrids exhibit electron injection from AlPorF3 to the conduction band of TiO2. However, the injection efficiencies and kinetics are not very different in the investigated stacks AlPorF3(Py)-COO/TiO2 and AlPorF3(Ph)-COO/TiO2 indicating that the axial self-assembly does not alter the electronic communication within the AlPorF3 layer to a significant level to perturb the photodynamics.

CO2‐based amphiphilic block copolymers: Facile one‐step synthesis and aqueous self‐assembly

AbstractConstruction of CO2‐based amphiphilic block copolymers (ABCs) is an efficient method for providing CO2‐based polycarbonates with self‐assembly properties in aqueous media. It is challenging to construct CO2‐based ABCs by one‐step strategies from mixed monomers because hydrophilic blocks, usually composed of polar monomers, have negative effects on the synthesis of polycarbonates. In this work, we report a one‐step method to construct CO2‐based ABCs obtained by simultaneous ring‐opening copolymerization (ROCOP) of CO2/epoxides and reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐isopropyl acrylamide (NIPAM). A trithiocarbonate/carboxy compound was used as the bifunctional chain transfer agent, and an aluminum porphyrin complex was used as the catalyst for ROCOP, which proved to be efficient in CO2 copolymerization even in the presence of NIPAM with strong polarity. This strategy allows flexible control over the molecular weight (5–16 kg/mol) and the hydrophilic‐hydrophobic balance (HLB 9–18) of the ABCs, and ensures narrow polydispersity Đ (1.1–1.3) of the polymers. The ABCs can further self‐assemble into micelles in water with controllable diameters and reversible phase transformation behavior with temperature changes from 25 to 40 °C. This simple route to CO2‐based ABCs with multiple functions has large potential in biomedical applications.

Catalytic synthesis and physical properties of CO2-based cross-linked poly(cyclohexene carbonate)s

Bifunctional aluminum porphyrins catalyzed the terpolymerization of cyclohexene oxide (CHO), bis(CHO), and CO2 to give cross-linked polycarbonates.

Polymeric aluminum porphyrin: Controllable synthesis of ultra-low molecular weight CO2-based polyols

Carbon dioxide-based polyols with ultra-low molecular weight (ULMW, Mn < 1000 g/mol) are emergent polyurethane precursors with economic and environmental benefits. However, the lack of effective proton-tolerant catalytic systems limits the development of this field. In this work, the polymeric aluminum porphyrin catalyst (PAPC) system was applied to the copolymerization of CO2 and propylene oxide, where sebacic acid, bisphenol A, poly(ethylene glycol), and water were used as chain transfer agents to achieve the controlled synthesis of CO2-polyols. The molecular weight of the resulting CO2-polyols could be facilely regulated in the range of 400–930 g/mol at low catalyst loadings, fully demonstrating its catalytic advantages of high activity, high product selectivity, and excellent proton tolerance of PAPC. Meanwhile, the catalytic efficiency of PAPC could reach up to 2.1–5.2 kg/g under organic CTA conditions, even reaching 1.9 kg/g using water as the CTA. The cPC content could be controlled within 1.0 wt% under the optimized conditions, indicating the excellent controllability of the PAPC system. ULMW CO2-polyols combines the advantages of low viscosity (∼3000 mPa s at 25 °C), low glass transition temperature (∼−73 °C), and high carbonate unit content (∼40%), which is important for the development of high-performance polyurethanes.

Bottlebrush polymeric catalyst: Boosting activity for CO2/epoxide copolymerization

A dynamic multi-cooperative strategy of constructing bottlebrush catalysts for the ring-opening copolymerization of carbon dioxide and propylene epoxide was developed. Nine bottlebrush polymeric aluminum porphyrin catalysts (BPAPC) were prepared through regulation of both brush length and bristle length, affording enhanced catalytic performances. Among them, BPAPC 5 with optimized topology exhibited a high activity (turnover frequency = 8,110 h−1) for the copolymerization of carbon dioxide and propylene epoxide, while maintaining high polymer selectivity of 99% at 110 °C. Notably, BPAPC 5 even could achieve a high turnover number of 39,000 at a very low catalyst loading ([PO]/[Al] = 50,000), yielding the copolymer with a number-average molecular weight of 271 kg∙mol−1. Moreover, through customizable catalyst design by manipulating steric confinement and ligand chemistry environment, the carbonate unit content of resulting polymers can be adjusted in the range of 35%–75%. Furthermore, the established balloon chain model explained the structure–function relationships of BPAPCs. This study provides a general design guide for cooperative catalytic systems.

Synthesis of Trimethylene Carbonates and Polycarbonates from Oxetanes and CO2 Using Bifunctional Aluminum Porphyrin Catalysts

Synthesis of Trimethylene Carbonates and Polycarbonates from Oxetanes and CO₂ Using Bifunctional Aluminum Porphyrin Catalysts

Two-in-One: Photothermal Ring-Opening Copolymerization of CO2 and Epoxides.

A two-in-one strategy for the photothermal ring-opening copolymerization (PROCOP) of carbon dioxide (CO2) and epoxides was developed by using visible light as an external stimulus. This strategy bridges two processes involving light-to-heat conversion and the alternating copolymerization of CO2 and epoxides. As a proof-of-concept, aluminum porphyrin complexes were explored as photothermal catalysts to afford the copolymerization of CO2/epoxides under a 635 nm laser irradiation. We demonstrated photothermally enhanced polymerization activity, in which the polymerization initiated by the photothermal effect showed a much higher turnover frequency than in the thermal system. Moreover, the PROCOP demonstrated a spatial-temporal control by a light on/off switch. This study provides a fascinating photothermal strategy not only for the CO2/epoxides copolymerization but also for the ring-opening (co)polymerization of other cyclic monomers.

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO 2 /Epoxide Copolymer

Unity Makes Strength: Constructing Polymeric Catalyst for Selective Synthesis of CO ₂ /Epoxide Copolymer

Sequential electron transfer in a bis(styryl)BODIPY-aluminum(III) porphyrin – naphthalenediimide reaction center mimic

Photoinduced electron transfer properties are reported for a triad composed of a central aluminum(III) porphyrin (AlPorF[Formula: see text] with a secondary electron donor, bis-triphenylaminoborondipyrromethene (TPA2-BDP) attached covalently to AlPorF3, and an electron acceptor, pyridine-appended naphthalenediimide (NDI), attached by coordination of the pyridine group to the AlPor on the opposite face. Excitation of either the AlPorF3 or BDP-TPA2 in the triad results in a two-step electron transfer leading to (TPA2-BDP)[Formula: see text]-AlPorF3-NDI[Formula: see text] as the final charge-separated species. The electron transfer is investigated using the steady-state fluorescence spectroscopy and time-resolved EPR spectroscopy. The behavior of the triad is compared to that of a previously reported triad in which the NDI acceptor was replaced with C[Formula: see text]. The two triads have virtually identical energetics, but the reorganization energies of the acceptors are known to be very different. The spectroscopic data show that the final charge-separated state is formed in both triads despite the large difference in the reorganization energy associated with the acceptors. This suggests that the ability to perform sequential electron transfer does not depend strongly on the properties of the final acceptor, provided that secondary electron transfer can outcompete recombination in the initial charge-separated state.

Magnetothermoelectric properties of Al-Porphyrin sandwiched by graphene nanoribbon electrode based on quantum interference

Rational design of single-molecular junction for efficient thermoelectric properties is a key prerequisite for thermoelectric conversion and fundamental challenge because of the existence of restrictive relationship between Seebeck coefficient and conductance. Inspired by the promising mechanism for promoting thermoelectric properties depended on spin-filter efficiency, magnetothermoelectric properties of aluminum porphyrin (Al-porphyrin) molecular junction have been investigated in contact with ferromagnetic graphene electrodes at different temperature. It is found that spin-resolved Seebeck coefficient is larger than charge-resolved Seebeck coefficient, leading to an excellent spin-resolved power factor about 0.3 pW/K2 at 0.25 eV for Al-porphyrin molecular junction. Ferromagnetic leads effectively realize thermal spin-filtering effect (SFE), which is induced by spin-resolved quantum interference (SQI) between graphene electrode and central nonmagnetic Al-porphyrin molecule. These results indicate the prospects of Al-porphyrin molecular junction applications in spin-caloritronics.

Facile Aluminum Porphyrin Complexes Enable Flexible Terminal Epoxides to Boost Properties of CO2‐Polycarbonate

AbstractIncorporation of flexible monomer is regarded as a valid way to the chemical modification of the highly brittle poly(cyclohexene carbonate) (PCHC), which derived from the copolymerization of CO2 and cyclohexene oxide (CHO). However, toxic metal catalyst such as cobalt dominates these terpolymerizations which against the green development philosophy. Here, a series of environmentally benign aluminum porphyrin catalysts with different steric and electronic effects for the terpolymerization of CO2, CHO, and terminal epoxides with various flexible pendant alkyl groups to adjust the properties of PCHC is reported. The resulting terpolymers display a random distribution of cyclohexene carbonate along the backbone with a regulated terminal epoxide insertion from 30% to 70%. Moreover, the mechanical properties can be well regulated in a wide range indicating the feasibility of the present approach. The present study provides a green way to chemical modification of rigid PCHC.

On-Demand Transformation of Carbon Dioxide into Polymers Enabled by a Comb-Shaped Metallic Oligomer Catalyst

In addition to harsh conditions, CO2 is an excess in most chemical transformations due to its sluggish reactivity. Herein, we realize the on-demand transformation of CO2 in the synthesis of poly(ether carbonate) polyols through a comb-shaped metallic oligomer catalyst, displaying quantitative reaction and product specificity. In contrast to conventional single-site catalysts that suffer from direct depolymerization long before quantitative CO2 conversion, the metallic oligomer catalyst anchoring multiple aluminum porphyrin complexes at the side chain maintains excellent polyol selectivity (>99%), exhibits high polymerization rate (turnover number of 50,000), and exquisitely places all CO2 monomers in the middle of the polyol backbone with oligoetherol end groups. The composition of polyol exactly corresponds to initial CO2 feed ratios of 0.07–0.39. Further studies on the kinetic rate law and activation parameters of key intermediates decipher the multimetallic synergistic catalysis. Hence, this work offers a fresh view of CO2 as an indeed countable monomer rather than ambiguous pressure as normally considered.

Copolymerization of carbon dioxide and oxetane catalyzed by aluminum porphyrin complex system

AbstractTetraphenylporphinatoaluminum chloride ([TPP]AlCl) catalyst and tetra‐n‐butylammonium bromide (TBAB) cocatalyst system is effective for the copolymerization of CO2 and oxetane even under low CO2 pressure (~2 MPa). In the presence of toluene as a solvent, poly(trimethylene carbonate) (PTMC) containing &gt;99% of carbonate linkages with Mn = 8600 and Mw/Mn = 1.70 was synthesized. This is the first report of PTMC formation with excellent ratio of carbonate linkages from oxetane and CO2. According to the kinetic analysis, proton nuclear magnetic resonance (1H NMR) and matrix assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF/MS) measurements of the products, PTMC was mainly synthesized via (i) the trimethylene carbonate (TMC) formation from CO2 and oxetane and (ii) the successive ring‐opening polymerization of TMC.

Photoinduced energy and electron transfer in a cofacial aluminum(III) porphyrin – Phosphorus(V) porphyrin heterodimer

A cofacial ‘aluminum(III) porphyrin – phosphorus(V) porphyrin’ (AlPor-Ph-PPor.PF6) heterodimer has been synthesized to investigate the factors that govern the energy and electron transfer processes in a direction perpendicular to the porphyrin plane. The AlPor and PPor+ are bound in the cofacial arrangement through a benzoate spacer. The electron-rich aluminum(III) porphyrin acts as an electron and energy donor, whereas the electron-poor phosphorus(V) porphyrin performs the role of electron and energy acceptor. Steady-state absorption studies and DFT calculations indicate that the energy states and orbitals of the two porphyrins are not significantly perturbed in the heterodimer compared to the corresponding monomers. However, fluorescence, femtosecond transient absorption and time-resolved electron paramagnetic resonance studies reveal that the excited state behavior of the heterodimer is very different from that of its constituent monomeric porphyrins. Excitation of the AlPor unit in the heterodimer results in both energy and electron transfer from the 1AlPor* to the PPor+ unit. The measured rate constants for energy and electron transfer in o-dichlorobenzene were found to be 2.9 × 109 s–1 and 5 × 109 s–1, respectively. The relative yield of the energy and electron processes can be modulated by changing the solvent polarity with energy transfer being slightly favored in less polar solvents. In contrast, excitation of the PPor+ unit results exclusively in electron transfer from the AlPor unit to 1(PPor+)*. Regardless of the excitation wavelength, the resulting charge-separated state eventually decays to the triplet state of the PPor+ unit. Finally, the photophysical properties of the investigated heterodimer, AlPor-Ph-PPor.PF6 are compared with a previously reported μ-oxo-heterodimer, AlPor-O-PPor.PF6, in which the distance between the AlPor and PPor+ is much shorter. In AlPor-O-PPor.PF6 the strong exciton coupling between AlPor and PPor+ leads to a charge transfer (CT) absorption, while in AlPor-Ph-PPor.PF6 neither of these features is observed because of the larger distance between the porphyrins.

Sequential Electron Transfer in a BODIPY–Aluminum(III) Porphyrin–C60 Triad Studied by Transient EPR Spectroscopy

Sequential Electron Transfer in a BODIPY–Aluminum(III) Porphyrin–C60 Triad Studied by Transient EPR Spectroscopy

Charge Stabilization in Axially Linked Donor – Aluminum(III) Porphyrin – Fullerene Reaction Center Models

In supramolecular reaction center models, the lifetime of the charge-separated state depends on many factors. However, little attention has been paid to the redox potential of the species that lie between the donor and acceptor in the final charge-separated state. Recently, we reported a series of self-assembled aluminum porphyrin-based triads that provide a unique opportunity to study the influence of the porphyrin redox potential independently of other factors. The triads, Donor-AlPorFn-C60, were constructed by linking the fullerene (C60) and Donor to the aluminum(III) porphyrin. The porphyrin (AlPor, AlPorF3, or AlPorF5) redox potentials are tuned by the substitution of phenyl (Ph), 3,4,5-trifluorophenyl (PhF3), or 2,3,4,5,6-pentafluorophenyl (PhF5) groups in its meso positions. The C60 and Donor (BTMPA) units are bound axially to opposite faces of the porphyrin plane via covalent and coordination bonds, respectively. Excitation of all of the triads results in sequential electron transfer that generates the identical final charge-separated state, BTMPA•+-AlPorFn-Ph-C60 •−, which lies energetically 1.50 eV above the ground state. Although the radical pair is identical in all of the triads, remarkably, the lifetime of the BTMPA•+-AlPorFn-Ph-C60 •− radical pair was found to be very different in each of them. I will discuss some of these systems in terms of their design principles and photoinduced properties. Figure 1