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Structural Characterization of Modular Supramolecular Architectures in Solution

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journal contribution
posted on 03.11.2004, 00:00 by David M. Tiede, Ruitian Zhang, Lin X. Chen, Lianhe Yu, Jonathan S. Lindsey
Structures of modular supramolecular architectures consisting of a hexameric, diphenylethyne-linked porphyrin macrocyclic array and the corresponding host−guest complex formed by inclusion of a tripyridyl guest molecule were characterized in solution using high-angle X-ray scattering. Scattering measurements made to 6 Å resolution coupled with pair distance function (PDF) analyses demonstrated that (1) the porphyrin architectures are not rigid but are distributed across a conformational ensemble with a mean diameter that is 1.5 Å shorter than the diameter of a symmetric, energy-minimized model structure, (2) the conformational envelope has limits of 3 Å positional dispersion and full rotational freedom for all six porphyrin groups, and (3) insertion of the tripyridyl guest molecule expands the diameter of the host conformer by 0.6 Å and decreases the configurational dispersion by approximately 2-fold. These results validate the molecular design, provide a new measure of conformational ensembles in solution that cannot be obtained by other techniques, and establish a structural basis for understanding the photophysical and guest−hosting functions of the hexameric porphyrin architectures in liquids.