Construction of Giant Porphyrin Macrorings Self-Assembled from Thiophenylene-Linked Bisporphyrins for Light-Harvesting Antennae

• Published in: Chemistry : a European journal 2008-11, Vol.14 (34), p.10735-10744
• Main Authors: Fujisawa, Kaori, Satake, Akiharu, Hirota, Shun, Kobuke, Yoshiaki
• Format: Article
• Language: English
• Subjects: coordination modes; Cyclization; Light-Harvesting Protein Complexes - chemistry; Macromolecular Substances - chemical synthesis; Macromolecular Substances - chemistry; Magnetic Resonance Spectroscopy - methods; Magnetic Resonance Spectroscopy - standards; Metalloporphyrins - chemical synthesis; Metalloporphyrins - chemistry; Molecular Structure; photosynthesis; porphyrinoids; Porphyrins - chemical synthesis; Porphyrins - chemistry; Reference Standards; self-assembly; Spectrometry, Fluorescence - methods; Spectrophotometry, Ultraviolet - methods; Stereoisomerism; Thiophenes - chemistry; Zinc - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200801466

As a model of bacterial photosynthetic light‐harvesting antenna, a large number of porphyrin units were organized into barrel‐shaped macrorings. Two imidazolylporphyrinatozinc(II) molecules were linked through either unsubstituted thiophenes or 3,4‐dioctylthiophenes 1 a and 1 b, respectively. These structures were spontaneously organized by complementary coordination of the imidazolyl to zinc and produced a series of self‐assembled fluorescent polygonal macrorings under high dilution conditions. The ring size increased compared with previous m‐phenylene examples. The size distribution was also controlled by the presence of octyl substituents. A wide distribution of macrorings from 7‐ to >15‐mer was obtained from 1 a, whereas macrorings ranging from 7‐ to 11‐mer with a maximum population focused at the 8‐mer were formed with 1 b. The size distribution was governed by competition between entropy‐favored, smaller‐ring formation and the enthalpy‐favored, less‐strained larger macroring. The UV/Vis spectra showed a gradual redshift for the larger rings reflecting an increase in the transition dipole interactions. Ring restrictions: Bis(imidazolylporphyrinatozinc(II)) units linked through either 3,4‐dioctylthiophenylenes or unsubstituted 2,5‐thiophenylene were joined by complementary coordination of imidazolyl to zinc to produce a series of self‐assembled fluorescent polygonal macrorings larger than hexagons under the appropriate reorganization conditions (see figure).