Alkylamine sensing using langmuir-blodgett films of n-alkyl-N-phenylamide-substituted zinc porphyrins

Two porphyrin compounds, zinc(II) 5,10,15,20-tetrakis(3,5,5-trimethyl- N-phenylhexanamide)porphyrin and zinc(II) 5,10,15,20-tetrakis(2,2-dimethyl- N-phenylpropanamide)porphyrin, have been investigated as possible candidates for the detection of alkylamines. UV-visible spectroscopy has shown that their solution absorption spectra are significantly modified upon interaction with a range of organic analytes, including acetic acid, butanone, ethylacetate, hexanethiol, octanal, octanol, alkylamines, and trimethylphosphite. Large spectral changes are observed for the family of alkylamines as a result of the specific affinity between zinc and the amine moiety. Langmuir-Blodgett (LB) films of the porphyrins have been fabricated in order to assess their solid-state sensing capability toward amines. The surface pressure-area (Pi- A) isotherms reveal a clear three-phase Langmuir film behavior and show that these monolayer films may be compressed to a relatively high surface pressure ( approximately 40-50 mN m (-1)). The isotherm data alongside molecular modeling suggest a relatively flat orientation of the porphyrin rings of both compounds: that is, a mutually parallel alignment of the plane of the porphyrin ring and that of the water surface. LB films deposited at 15 mN m (-1) have been exposed to alkylamine vapor (carried by N 2). A red shift and increase in intensity of the Soret band absorbance is observed which can be reversed by flowing pure N 2 over the gently heated sample (60 degrees C) after exposure. Primary amines were expected to invoke the greatest sensing response due to (i) their larger association constants with these porphyrins compared to secondary and tertiary amines and (ii) the ease of diffusion of amines which is expected to follow the order primary > secondary > tertiary due to the steric hindrance arising from the bulky secondary and tertiary amines. However, the magnitude of the absorbance change is largest for exposure to the secondary amines, dipropylamine and dibutylamine, for both porphyrins, compared to primary and tertiary amines. This trend follows that observed when the amines were added to solutions of the porphyrins. The rate of response of the porphyrin LB films falls as the molecular weight of the diffusing alkylamine increases. Furthermore, a greater rate of response is observed for the phenylhexanamide porphyrin compared to the phenylpropanamide porphyrin due to its lower molecular density within the LB film and therefore more porous structure.     

2D sp2 Carbon‐Conjugated Porphyrin Covalent Organic Framework for Cooperative Photocatalysis with TEMPO

2D covalent organic frameworks (COFs) are receiving ongoing attention in semiconductor photocatalysis. Herein, we present a photocatalytic selective chemical transformation by combining sp² carbon‐conjugated porphyrin‐based covalent organic framework (Por‐sp²c‐COF) photocatalysis with TEMPO catalysis illuminated by 623 nm red light‐emitting diodes (LEDs). Highly selective conversion of amines into imines was swiftly afforded in minutes. Specifically, the π‐conjugation of porphyrin linker leads to extensive absorption of red light; the sp² ?C=C? double bonds linkage ensures the stability of Por‐sp²c‐COF under high concentrations of amine. Most importantly, we found that crystalline framework of Por‐sp²c‐COF is pivotal for cooperative photocatalysis with (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO). This work foreshadows that the outstanding hallmarks of COFs, particularly crystallinity, could be exploited to address energy and environmental challenges by cooperative photocatalysis.     

Controllable Synthesis of Porphyrin‐Based 2D Lanthanide Metal–Organic Frameworks with Thickness‐ and Metal‐Node‐Dependent Photocatalytic Performance

Synthesizing 2D metal–organic frameworks (2D MOFs) in high yields and rational tailoring of the properties in a predictable manner for specific applications is extremely challenging. Now, a series of porphyrin‐based 2D lanthanide MOFs (Ln‐TCPP, Ln=Ce, Sm, Eu, Tb, Yb, TCPP=tetrakis(4‐carboxyphenyl) porphyrin) with different thickness were successfully prepared in a household microwave oven. The as‐prepared 2D Ln‐TCPP nanosheets showed thickness‐dependent photocatalytic performances towards photooxidation of 1,5‐dihydroxynaphthalene (1,5‐DHN) to synthesize juglone. Particularly, the Yb‐TCPP displayed outstanding photodynamic activity to generate O₂^? and ¹O₂. This work not only provides fundamental insights into structure designing and property tailoring of 2D MOFs nanosheets, but also pave a new way to improve the photocatalytic performance.     

Designed Synthesis of a 2D Porphyrin‐Based sp2 Carbon‐Conjugated Covalent Organic Framework for Heterogeneous Photocatalysis

The construction of stable covalent organic frameworks (COFs) for various applications is highly desirable. Herein, we report the synthesis of a novel two‐dimensional (2D) porphyrin‐based sp² carbon‐conjugated COF (Por‐sp²c‐COF), which adopts an eclipsed AA stacking structure with a Brunauer—Emmett—Teller surface area of 689 m² g^?1. Owing to the C=C linkages, Por‐sp²c‐COF shows a high chemical stability under various conditions, even under harsh conditions such as 9 m HCl and 9 m NaOH solutions. Interestingly, Por‐sp²c‐COF can be used as a metal‐free heterogeneous photocatalyst for the visible‐light‐induced aerobic oxidation of amines to imines. More importantly, in comparison to imine‐linked Por‐COF, the inherent structure of Por‐sp²c‐COF equips it with several advantages as a photocatalyst, including reusability and high photocatalytic performance. This clearly demonstrates that sp² carbon‐linked 2D COFs can provide an interesting platform for heterogeneous photocatalysis.     

2D sp2 Carbon-Conjugated Porphyrin Covalent Organic Framework for Cooperative Photocatalysis with TEMPO

2D covalent organic frameworks (COFs) are receiving ongoing attention in semiconductor photocatalysis. Herein, we present a photocatalytic selective chemical transformation by combining sp² carbon-conjugated porphyrin-based covalent organic framework (Por-sp²c-COF) photocatalysis with TEMPO catalysis illuminated by 623 nm red light-emitting diodes (LEDs). Highly selective conversion of amines into imines was swiftly afforded in minutes. Specifically, the π-conjugation of porphyrin linker leads to extensive absorption of red light; the sp² −C=C− double bonds linkage ensures the stability of Por-sp²c-COF under high concentrations of amine. Most importantly, we found that crystalline framework of Por-sp²c-COF is pivotal for cooperative photocatalysis with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). This work foreshadows that the outstanding hallmarks of COFs, particularly crystallinity, could be exploited to address energy and environmental challenges by cooperative photocatalysis.     

Photocatalytic CO2 Reductions Catalyzed by meso-(1,10-Phenanthrolin-2-yl)-Porphyrins Having a Rhenium(I) Tricarbonyl Complex

We have prepared Zn and free-base porphyrins appended with a fac-Re(phen)(CO)₃Br (where phen is 1,10-phenanthroline) at the meso position of the porphyrin, and performed photocatalytic CO₂ reduction using porphyrin–Re dyads in the presence of either triethylamine (TEA) or 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. The Zn porphyrin dyad showed a high turnover number for CO production compared with the free-base porphyrin dyad, suggesting that the central Zn ion of porphyrin plays an important role in suppressing electron accumulation on the porphyrin part and achieving high durability of the photocatalytic CO₂ reduction using both TEA and BIH. The effect of acids on the CO₂ reduction was investigated using the Zn porphyrin–Re dyad and BIH. Acetic acid, a relatively strong Brønsted acid, rapidly causes the porphyrin's color to fade upon irradiation and dramatically decreases CO production, whereas proper weak Brønsted acids such as 2,2,2-trifluoroethanol and phenol enhance the CO₂ reduction.     

Carbon-nitrogen bond activation of amines by rhodium(III) porphyrin complexes

Carbon-nitrogen bond activation of amines by rhodium porphyrin chloride has been achieved to give rhodium porphyrin alkyl complexes. Rhodium porphyrin hydride and rhodium porphyrin dimer were proposed as the intermediates in cleaving the C-N bond.     

Absolute configurational assignments of secondary amines by CD-sensitive dimeric zinc porphyrin host

A general chiroptical protocol for determination of absolute configuration of secondary amines including acyclic and cyclic aliphatic amines, aromatic amines, amino acids, and amino alcohols is described. The chiral substrate is linked to the achiral carrier moiety (3-N-Boc-amino-propyl-N-Boc-amino)acetic acid 1 (BocHNCH(2)CH(2)CH(2)BocNCH(2)COOH), which after deprotection, yields a bidentate conjugate, capable of forming a 1:1 host/guest complex with dimeric zinc porphyrin host 2. As in the cases of primary amines and secondary alcohols reported earlier, the complexation of secondary amine conjugates to porphyrin tweezer host 2 represents a stereodifferentiating process, where the large (L) group at the stereogenic center (assigned on the basis of conformational energies A value) protrudes from the porphyrin binding pocket. This leads to formation of host/guest complexes with a preferred porphyrin helicity that exhibit intense exciton split CD spectra. It was found that the chiral sense of porphyrin twist is clearly controlled by the stereogenic center despite the Z/E conformational complexity around the tertiary amide bond of secondary amine conjugates that has greatly hampered previous configurational assignments. Thus, in cases where there is no ambiguity regarding the relative steric size of substituents, the observed CD couplet can be applied for straightforward assignment of absolute configurations. In addition, to extend the application to more difficult cases a molecular mechanics calculation approach using the Merck Molecular Force Field (MMFFs) was developed; this provides conformational information of host/guest complexes and leads to prediction of preferred porphyrin helicity independent of conformational A values. This chiroptical protocol in combination with molecular modeling represents a general method for configurational assignments of secondary amines.     

卟啉敏化的钛酸盐纳米管的可见光催化活性

制备了四碘化5,10,15,20-四(对-N,N,N三甲基苯胺基)卟啉敏化的钛酸盐纳米管(TAPPI-TNTs),并利用甲基橙(MO)作为模型污染物考察了其可见光催化活性。结果表明,TAPPI-TNTs是一个高效的可见光催化剂,在其催化作用下,可见光照射1 h后,甲基橙的降解率为89%。与此相反,纯钛酸盐纳米管并不具有可见光催化活性。此外,TAPPI-TNTs的稳定性较高,可以多次循环使用,在第五次循环中,甲基橙的降解率仍可达到50%以上。这可能是由于带正电荷的卟啉与带负电荷的钛酸盐纳米管之间存在着较强的静电吸引作用,卟啉紧密地吸附在钛酸盐纳米管上,导致卟啉的光激发电子易于向钛酸盐纳米管转移,从而使钛酸盐纳米管得到了有效敏化。     

General and efficient synthesis of arylamino- and alkylamino-substituted diphenylporphyrins and tetraphenylporphyrins via palladium-catalyzed multiple amination reactions

A series of arylamino- and alkylamino-substituted diphenylporphyrins and tetraphenylporphyrins were efficiently synthesized by reactions of brominated porphyrin precursors with amines via palladium-catalyzed amination. The multiple amination reactions are general and suitable for a variety of amines, affording the desired aminoporphyrins in good to excellent yields. Examples include aromatic and aliphatic amines, primary and secondary amines, electron-rich, -neutral, and -poor amines as well as heteroaromatic amines and imines.     

卟啉网状结构材料负载单原子的光催化CO2还原

基于刚性、多孔性和多功能性,以及模块化优化、合理的设计和集成、可调谐和光化学性能等优点,卟啉网状结构材料已被证明是金属单原子锚定的优良载体,并在CO₂光催化还原领域拓展了一种新的载体.我们主要总结了近5年来以反应卟啉网状结构材料为载体的单原子催化剂光催化CO₂还原反应的最新研究进展,提出并探讨了该多相催化剂光催化CO₂还原的应用前景以及面临的挑战.     

Photocatalytic Carboxylation of C−N Bonds in Cyclic Amines with CO2 by Consecutive Visible-Light-Induced Electron Transfer

Visible-light photocatalytic carboxylation with CO₂ is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel photocatalytic carboxylation of C−N bonds in cyclic amines with CO₂ via consecutive photo-induced electron transfer (ConPET). It is also the first photocatalytic reductive ring-opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β-, γ-, δ- and ϵ-amino acids in moderate-to-excellent yields. Moreover, the method also features mild and transition-metal-free conditions, high selectivity, good functional-group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.     

Cu-clusters nodes of 2D metal-organic frameworks as a cost-effective noble-metal-free cocatalyst with high atom-utilization efficiency for efficient photocatalytic hydrogen evolution

Several 2D nanosheets of porphyrin MOFs with various transition-metal clusters as metal nodes were prepared via a simple solvothermal method to apply in the photocatalytic hydrogen evolution,in which the hydrogen production rate of the optimal NS-Cu was as high as 15.39 mmol g^-1h^-1.A series of experimental technologies especially cyclic voltammetry （CV） and Mott-Schottky （M-S） had been adopted to investigate the charge-transfer property of photo-generated electron-hole pair...     

Controllable Synthesis of Porphyrin-Based 2D Lanthanide Metal–Organic Frameworks with Thickness- and Metal-Node-Dependent Photocatalytic Performance

Synthesizing 2D metal–organic frameworks (2D MOFs) in high yields and rational tailoring of the properties in a predictable manner for specific applications is extremely challenging. Now, a series of porphyrin-based 2D lanthanide MOFs (Ln-TCPP, Ln=Ce, Sm, Eu, Tb, Yb, TCPP=tetrakis(4-carboxyphenyl) porphyrin) with different thickness were successfully prepared in a household microwave oven. The as-prepared 2D Ln-TCPP nanosheets showed thickness-dependent photocatalytic performances towards photooxidation of 1,5-dihydroxynaphthalene (1,5-DHN) to synthesize juglone. Particularly, the Yb-TCPP displayed outstanding photodynamic activity to generate O₂⁻ and ¹O₂. This work not only provides fundamental insights into structure designing and property tailoring of 2D MOFs nanosheets, but also pave a new way to improve the photocatalytic performance.     

Synthesis of Novel Symmetric Porphyrin Schiff Base Dimers by Solid–Liquid Reaction Methodology

A new convenient solid–liquid condensation reaction procedure for the synthesis of novel asymmetric and symmetric meso‐tetraarylporphyrin and metalloporphyrin Schiff bases is reported. The condensation reaction between β‐formyl porphyrin or metalloporphyrins and aromatic amines was carried out at solid–liquid interface by using neutral alumina powder as a solid support for β‐formyl porphyrin or metalloporphyrins and absolute ethanol as the carrier solvent for aromatic amines. Six different asymmetric porphyrin/metalloporphyrin Schiff bases were synthesized via solid–liquid interface reaction methodology. The same solid–liquid synthetic methodology was applied for the synthesis of six novel symmetric Schiff base porphyrin/metalloporphyrin dimers. The comparison of UV–visible spectra of porphyrin Schiff base monomers and dimers revealed that some degree of electronic perturbation has occurred upon dimerization as the Soret bands of the monomers underwent peak broadening along with red shifts. Column chromatography and crystallization were used to purify the compounds. Fourier transform infrared, UV–visible, elemental analysis, ¹H NMR, and mass spectrometry were used to characterize the newly synthesized compounds.     

Supramolecular chirogenesis in zinc porphyrins: mechanism, role of guest structure, and application for the absolute configuration determination.

The achiral syn folded (face-to-face conformation) host molecule of the ethane-bridged bis(zinc porphyrin) transforms into the corresponding chiral extended anti bis-ligated species in the presence of enantiopure amine guests. The mechanism of the supramolecular chirogenesis is based upon the screw formation in bis(zinc porphyrin), arising from steric interactions between the largest substituent at the ligand's asymmetric carbon and peripheral alkyl groups of the neighboring porphyrin ring pointing toward the covalent bridge. The screw direction is determined by the guest's (amines) absolute configuration resulting in a positive chirality induced by (S)-enantiomers due to formation of the right-handed screw, and a negative chirality produced by the left-handed screw of (R)-enantiomers. The screw magnitude is strongly dependent upon the structure of the chiral guests. The amines with bulkier substituents result in stronger CD signals and larger (1)H NMR resonance splittings of enantiotopic protons. This system possesses a high degree of chiroptical activity, which allows the differentiation of one of the smallest homologous elements of organic chemistry, that is, the methyl and ethyl groups attached to the asymmetric carbon, and additionally, which senses a remote chiral center at a position beta to the amine binding group.     

Mimicking the environment of living organisms to achieve the oxidative coupling of amines to imines catalyzed by water-soluble metalloporphyrins

Highly efficient procedure for preparing imines from the oxidative coupling of amines catalyzed by metalloporphyrins using water as the only solvent has been developed. Manganese porphyrin showed an excellent activity for the oxidative coupling of a wide range of amines under mild conditions. Further investigations of the oxidative coupling reaction led to the elucidation of the possible mechanism.     

Supramolecular chirogenesis in zinc porphyrins: equilibria, binding properties, and thermodynamics

Complexation mechanism, binding properties and thermodynamic parameters of supramolecular chirality induction in the achiral host molecule, syn (face-to-face conformation) ethane-bridged bis(zinc porphyrin), upon interaction with chiral monoamine and monoalcohol guests have been studied by means of the UV-vis, CD, (1)H NMR, and ESI MS techniques. It was found that the chirogenesis process includes three major equilibria steps: the first guest ligation to a zinc porphyrin subunit of the host (K(1)), syn to anti conformational switching (K(S)), and further ligation by a second guest molecule to the remaining ligand-free zinc porphyrin subunit (K(2)), thus forming the final bis-ligated species possessing supramolecular chirality. The validity of this equilibria model is confirmed by the excellent match between the calculated and experimentally observed spectral parameters of the bis-ligated species. The second ligation proceeds in a cooperative manner as K(2) > K(1) for all supramolecular systems studied, regardless of the structure of the chiral ligand used. The binding properties are highly dependent on the nature of the functional group (amines are stronger binders than alcohols) and on the structure of the chiral guests (primary and aliphatic amines have overall binding constant values greater than those of secondary and aromatic amines, respectively).     

Sensitized Photochemical CO2 Reduction by Hetero-Pacman Compounds Linking a ReI Tricarbonyl with a Porphyrin Unit

The hetero-Pacman architecture places two different metal coordination sites in close proximity, which can support efficient energy and/or electron transfer and allow for cooperative activation of small molecules. Here, the synthesis of dyads consisting of a porphyrin unit as photosensitizer and a rhenium unit as catalytically active site, which are held together by the rigid xanthene backbone, is presented. Mononuclear [(NN)Re(CO)₃(Cl)] complexes for CO₂ reduction in which NN represents a bidentate diimine ligand (e.g., bipyridine or phenanthroline) lack light absorption in the visible region, resulting in poor photocatalysis upon illumination with visible light. To improve their visible-light absorption, we have focused on the incorporation of a strongly absorbing free base or zinc porphyrin unit. Resulting photocatalytic experiments showed a strong dependence of the catalytic performance on both the type of photosensitizer and the excitation wavelengths. Most notably, the intramolecular hetero-Pacman system containing a zinc porphyrin unit showed much better catalytic activity in the visible region (excitation wavelengths >450 nm) than the free base porphyrin version or the corresponding mononuclear rhenium compound or an intermolecular system comprised of a 1:1 mixture of the mononuclear analogues.     

金属卟啉/异烟酸/二氧化钛复合光催化剂制备及其光催化性能研究

合成了四苯基卟啉(H2TPP)及铜卟啉(CuTPP)和锌卟啉(ZnTPP),获得了配合物[Zn(TPP)(DMF)]的晶体。制备了金属卟啉、异烟酸共修饰的二氧化钛复合光催化剂:金属卟啉/异烟酸/二氧化钛,红外光谱和X-射线衍射(XRD)分析结果表明金属卟啉和异烟酸负载于TiO2表面,未改变TiO2的晶型。在光催化降解水中污染物4-硝基苯酚(4-NP)时显示了好的催化效果。