Max Martin

Contemporary applications in optics, medicine, solar cells, or material science are increasingly reliant on unsymmetrically substituted porphyrins. Due to their widespread applications and rise in demand we undertook a comparative analysis of synthetic strategies for meso-substituted porphyrins and present the synthesis of five different series of so-called A₂BC push-pull porphyrins. The synthetic pathways used were applied to both 5,15-substituted and 5,10-substituted porphyrins, showcasing their flexibility and adaptability for different needs. Our approach combines well-known reactions with a strategic and logical stepwise functionalization allowing researchers to change and modify the electronic properties of these systems at various points of the syntheses. This facilitates the easy optimization of the synthesis of systems of current interest, for example, porphyrins for dye-sensitized solar cells (DSSCs) or for use in nonlinear optics, as well as fast generation of compound libraries.

In view of the applications of A₂BC push-pull porphyrins, for example in dye-sensitized solar cells (DSSCs), we analyzed the synthetic strategies for 5,10- and 5,15-substituted porphyrins, combining well-known reactions with a strategic and logical stepwise functionalization, enabling the modification of the electronic properties of these systems at various points of the syntheses.

A series of luminescent bis-cyclometalated gold(III) complexes with different nuclearities and various alkynyl ligands derived from hexaphenylbenzene (HPB) and hexabenzocoronene (HBC) have been synthesized. The energies of the low-energy metal-perturbed intraligand (IL) π–π*(R−C^N^C) absorptions of the HPB–alkynyl gold(III) complexes have been fine-tuned by attaching various substituent groups to the bis-cyclometalating ligands. Similarly, the metal-perturbed ³IL [ππ*(R−C^N^C)] emissions of the complexes show energy shifts according to the electronic nature of the bis-cyclometalating ligands. On the contrary, the absorption and emission spectra of the HBC–alkynyl gold(III) complex have been assigned as dominated by the IL transitions of the HBC–alkynyl unit, as supported by transient absorption studies. The supramolecular assembly morphologies of the gold(III) complexes have been studied by TEM and SEM, along with comparisons across different complexes based on the molecular structures, and their assembly processes monitored by concentration-dependent and variable-temperature ¹H NMR spectroscopy studies.

Glitters with gold(III): A new class of luminescent bis-cyclometalated gold(III) complexes, containing hexa-peri-hexabenzocoronene or hexaphenylbenzene derivatives in the alkynyl ligands, has been synthesized and characterized (see figure). The complexes undergo supramolecular self-assembly processes driven by noncovalent interactions. Detailed spectroscopic studies were performed.

The Scholl-type reactions of 4,10-disubstituted chrysene derivatives proceeded by variegated and unexpected oxidation/coupling pathways. These observations serve as a cautionary note when attempting to employ the Scholl reaction in target-oriented materials synthesis.

Scholl coupling reactions proceed by unexpected oxidation/coupling pathways.

A feasible two-step synthesis and characterization of a full series of hexaarylbenzene (HAB) substituted porphyrins and tetrabenzoporphyrins is presented. Key steps represent the microwave-assisted porphyrin condensation and the statistical Diels–Alder reaction to the desired HAB-porphyrins. Regarding their applications, they proved to be easily accessible and effective high molecular mass calibrants for (MA)LDI mass spectrometry. The free-base and zinc(II) porphyrin systems, as well as the respective tetrabenzoporphyrins, demonstrate in solid state experiments strong red- and near-infrared-light emission and are potentially interesting for the application in “truly organic” light-emitting devices. Lastly, they represent facile precursors to large polycyclic aromatic hydrocarbon (PAH) substituted porphyrins. We prepared the first tetra-hexa-peri-hexabenzocoronene substituted porphyrin, which represents the largest prepared PAH-porphyrin conjugate to date.

Hexaarylbenzene (HAB)-substituted (tetrabenzo)porphyrins were found to have useful properties for various applications, such as calibrants for (MA)LDI instruments, as strong red- and near- infrared light emitters, and as precursors to large superbenzene-porphyrin light-harvesting architectures.

The catalytic hydrocarboxylation of styrenes derivatives and α,β-unsaturated carbonyl compounds with CO₂ (101.3 kPa) in the presence of an air-stable rhodium catalyst was explored. The combination of [RhCl(cod)]₂ (cod = cyclooctadiene) as a catalyst and diethylzinc as a hydride source allowed for effective hydrocarboxylation and provided the corresponding α-aryl carboxylic acids in moderate to excellent yields. In this catalytic process with carbon dioxide, intervention of the Rh^I–H species, which could be generated from the Rh^I catalyst and diethylzinc, was clarified. Significantly, the catalytic asymmetric hydrocarboxylation of α,β-unsaturated esters with carbon dioxide was also performed by employing a cationic rhodium complex possessing (S)-(–)-4,4′-bi-1,3-benzodioxole-5,5′-diylbis(diphenylphosphine) [(S)-SEGPHOS] as a chiral diphosphine ligand. A plausible model for asymmetric induction was proposed by determination of the absolute configuration of the product.

The Rh-catalyzed hydrocarboxylation of styrene derivatives and α,β-unsaturated carbonyl compounds with CO₂ is shown. The use of [RhCl(cod)]₂ (cod = cyclooctadiene) as a catalyst and diethylzinc as a hydride source provides the corresponding α-aryl carboxylic acids in moderate to excellent yields. Additionally, this catalyst system can be used in the asymmetric version of this reaction.