Collapsed Molecular Rectangles Based on Rhenium(I) Coordination of Ethynylpyridyl Porphyrins − Synthesis, Structure, and Bending-Induced Charge-Transfer Behavior

Abstract

Efforts to synthesize extremely large rectangle-shaped porphyrin systems have yielded an unusual and unexpected collapsed structure that brings the porphyrin walls into van der Waals contact. The bent geometry of the nominally rigid ethynylpyridyl porphyrin ligand edges, mandated by the collapse of the rectangle, imparts significant charge-transfer character to the rectangles' Soret and Q-region electronic transitions, as shown experimentally by Stark spectroscopy and transient DC photoconductivity measurements, and replicated by electronic structure calculations. In contrast to lower symmetry porphyrin-like pairs found in naturally occurring photosystems, however, the light-induced charge transfer is an intra-porphyrin rather than inter-porphyrin process. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)