Thermodynamics and kinetics of guest-induced switching between "basket handle" porphyrin isomers

Selective Convergence to Atropisomers of a Porphyrin Derivative Having Bulky Substituents at the Periphery

Four kinds of possible atropisomers of a porphyrin derivative (1), having mesityl groups at one of the o-positions of each meso-aryl group, can be selectively converged to targeted atropisomers among the four isomers (αααα, αααβ, αβαβ, and ααββ) under appropriate conditions for each atropisomer. For example, protonation and subsequent neutralization of a free base porphyrin (H₂-1) induces a convergence reaction to the αβαβ atropisomer, H₂-1-αβαβ, from an atropisomeric mixture. The αααα isomer, H₂-1-αααα, was also obtained by heating a solution of H₂-1 in CHCl₃ in 60% isolated yield, probably owing to a template effect of the solvent molecule. Remarkably, when an atropisomeric mixture of its zinc complex, Zn-1, was heated at 70 °C in a ClCH₂CH₂Cl/MeOH mixed solvent, crystals composed of only Zn-1-αααα were formed. The hydrophobic space formed by the four mesityl groups in the αααα isomer can be used for repeatable molecular encapsulation of benzene, and the encapsulation structure was elucidated by powder X-ray diffraction analysis. Heating the solid of an atropisomeric mixture of Zn-1 to 400 °C afforded the ααββ isomer almost quantitatively. On the other hand, the solid of H₂-1-αααα can be converted by heating, successively to H₂-1-αααβ at 286 °C and then to H₂-1-ααββ at 350 °C.

Porphyrin cage compounds based on glycoluril – from enzyme mimics to functional molecular machines

This Feature Article gives an overview of the application of glycoluril-based porphyrin cage compounds in host–guest chemistry, allosterically controlled self-assembly, biomimetic catalysis, and polymer encoding.

Structure and dynamics processes in free-base chlorins controlled by chemical modifications of macroring and aryl groups in meso-positions

The synthesis, detailed structural characterization and analysis of molecular motion for unsymmetrical pyrrolidine-fused chlorins employing NMR, UV spectroscopy and DFT theoretical calculations are presented.

General Scheme for Oxidative Quenching of a Copper Bis-Phenanthroline Photosensitizer for Light-Driven Hydrogen Production

A new, general reaction scheme for photocatalytic hydrogen production is presented based on oxidative quenching of a homoleptic copper(I) bis-1,10-phenanthroline photosensitizer (PS) by 1-methyl-4-phenyl-pyridinium (MPP(+) ) as the electron relay and subsequent regeneration of the so formed copper(II) complex by a sacrificial electron donor. Electron transfer from the relay to various cobalt based water reduction catalysts and subsequent H2 production was shown to close the catalytic cycle. Transient absorption experiments unambiguously confirmed the proposed pathway, both the oxidative quenching and subsequent regeneration of oxidized PS. Photocatalytic test runs further confirmed the role of MPP(+) and up to 10 turnovers were achieved in the relay. The performance limiting factor of the system was shown to be the decomplexation of the copper PS. Quantum yields of the system were 0.03 for H2 production, but 0.6 for MPP(.) formation, clearly indicating that unproductive pathways still prevail.