Porphene and porphite as porphyrin analogs of graphene and graphite

Antiaromaticity in molecular assemblies and materials

Antiaromatic rings are infamously unstable and difficult to work with but they possess unusual electronic properties that make them interesting for fundamental and applied research. This perspective presents reports on discrete or polymeric assemblies made from antiaromatic building blocks, bound by either covalent linkages or supramolecular interactions. Compared to polymeric materials, discrete assemblies are more commonly studied, but most efforts have been devoted to their preparation and fundamental property studies, whereas applications are scarcely suggested. Future research in the field should focus on developing applications that benefit from the specific properties of antiaromatic rings. On the other hand, the few reports on antiaromatic-based materials hint at a promising future for this class of materials in organic electronics. To guide non-experts, different antiaromatic compounds are evaluated for their suitability as building blocks for larger assemblies.

Mini-Review on Catalytic Hydrogen Evolution from Porphyrin-Graphene Structures

Porphyrin-based derivatives have been extensively investigated in photocatalytic, electrocatalytic, and photoelectrocatalytic H2 production systems as both photosensitizers and catalysts. Recently, their combination with two-dimensional materials, such as graphene oxide, reduced graphene oxide, and graphene quantum dots, has attracted significant attention for hydrogen evolution due to the advanced electronic properties, good stability, and low-cost fabrication of these materials. This mini-review summarizes the recent developments concerning the application of porphyrin-graphene ensembles in catalytic H2 generation. Current challenges concerning this application are discussed, and future perspectives are also proposed.

Nanosized Porphyrin-Containing Covalent Organic Polymer to Enhance Ferroptosis in Photodynamic Treatment of Tumor Cells via Glutathione Depletion

A porphyrin-containing nanoscale covalent organic polymer (COP) was fabricated from 5,10,15,20-tetra(4-carboxyphenyl)porphyrin (TCPP) and cystamine via an acylation reaction. On the one hand, TCPP can induce tumor cell death by laser irradiation. Due to the presence of disulfide bonds of cystamine which can react with glutathione, it exhibits depletion of glutathione and accumulation of peroxides in tumor cells. Ultimately by the hyaluronic acid to encapsulate the COP to get S-COP@HA, the nanoparticle with a size of 168.6 nm also exhibits good tumor accumulation and biosafety. Significant inhibition of tumor cell growth was observed after two consecutive doses of S-COP@HA at relatively low laser densities. This combination therapy was proved to reduce the level of reduced glutathione in tumor cells, where ferroptosis occurs after photodynamic treatment. Overall, this study presents a potent, good therapeutic option for the effective enhancement of photodynamic therapy by glutathione depletion.

Electronic Structure of Metalloporphenes, Antiaromatic Analogues of Graphene

Zinc porphene is a two-dimensional material made of fully fused zinc porphyrins in a tetragonal lattice. It has a fully conjugated π-system, making it similar to graphene. Zinc porphene has recently been synthesized, and a combination of rough conductivity measurements and infrared and Raman spectroscopies all suggested that it is a semiconductor (Magnera, T.F. et al. Porphene and Porphite as Porphyrin Analogs of Graphene and Graphite, Nat. Commun.2023, 14, 6308). This is in contrast with all previous predictions of its electronic structure, which indicated metallic conductivity. We show that the gap-opening in zinc porphene is caused by a Peierls distortion of its unit cell from square to rectangular, thus giving the first account of its electronic structure in agreement with the experiment. Accounting for this distortion requires proper treatment of electron delocalization, which can be done using hybrid functionals with a substantial amount of exact exchange. Such a functional, PBE38, is then applied to predict the properties of many first transition row metalloporphenes, some of which have already been prepared. We find that changing the metal strongly affects the electronic structure of metalloporphenes, resulting in a rich variety of both metallic conductors and semiconductors, which may be of great interest to molecular electronics and spintronics. Properties of these materials are mostly governed by the extent of the Peierls distortion and the number of electrons in their π-system, analogous to changes in aromaticity observed in cyclic conjugated molecules upon oxidation or reduction. These results give an account of how the concept of antiaromaticity can be extended to periodic systems.

Local Cyclic Voltammetry of a Langmuir-Blodgett Film on Water

An electrochemical Langmuir-Blodgett trough that permits an examination of local redox processes in a layer floating on the surface of water with a scanning tunneling microscopy-tip ultramicroelectrode has been constructed and tested on a layer of 1,1'-dicarbooctadecyloxyferrocene.