No abstract

The power of supramolecular chemistry to solve problems in structural chemistry where conventional techniques such as NMR, UV, and IR spectroscopy failed is demonstrated in the differentiation of the syn‐ and anti‐bis(capped porphyrin) isomers (obtained after condensation of a capped porphyrin monomer) by simple UV/Vis binding studies using bidentate ligands that act as “molecular rulers” (see picture).

The dynamics of electronic energy transfer (EET) for a series of spherical porphyrin arrays based on different generations of poly(propylene imine) dendrimers have been investigated using time-resolved fluorescence anisotropy measurements (TRAMS) in a glass environment. The first, third, and fifth generation dendrimers consisting of 4, 16, and 64 porphyrin chromophores, respectively, are investigated in this study. We observe a depolarization of the fluorescence in all three dendrimers as compared to the monoporphyrin model compound, indicating that EET takes place between the chromophores within the dendrimers. The experimental TRAMS results were compared to computationally simulated data obtained from the Pauli master equation. For the first generation dendrimer, we find the rate of energy transfer is well described by Förster theory. Anomalous behavior is observed in the third generation dendrimer where the limiting anisotropy value suggests that energy transfer is confined to only the porphyrins contained within a dendron. Interdendron porphyrin EET is thus unfavorable due to dendron segregation. In the fifth generation dendrimer, the TRAMS data is best explained by a model which includes independent and simultaneous rapid EET between porphyrins contained on the surface of the dendrimer sphere and slow EET between porphyrins in adventitious dendrons found probably either outside or inside of the sphere.

The title complex (I) crystallizes in P21/n with Z=4.

Beschleunigt durch ein aromatisches Gastmolekül in der Tasche des U‐förmigen Wirtes 1 wird der photoinduzierte Elektronentransfer zwischen der Zinkporphyrin‐ und der Chinoneinheit (R = tBu). Dieser Beschleunigung liegt eine Elektronenübertragung nicht über kovalente Bindungen, sondern durch den Raum zugrunde. Der Befund erinnert an das Verhalten einiger aromatischer Proteinreste in manchen Photosynthesezentren.