title: 2-Aminopyrimidine directed self-assembly of zinc porphyrins containing bulky 3,5-di-tert-butylphenyl groups.
abstract: The 2-aminopyrimidin-5-yl ligand is revealed to be a promising candidate for the construction of supramolecular porphyrin arrays with broad absorption bands for efficient light-harvesting. 10-Mono- and 10,20-di(2-aminopyrimidin-5-yl) derivatives of 5,15-bis(3,5-di-tert-butylphenyl)porphyrin have been synthesized in high yield. Their Zn(II) salts show variable concentration and temperature-dependent UV/vis spectra in solution, consistent with supramolecular aggregation. Whereas the FAB mass spectra of the monosubsituted derivative in toluene suggest the formation of a tetramer at high concentrations and low temperatures (estimated association free enthalpy Delta H = 220 +/- 10 kJ/mol), the larger splitting of the Sorret band (ca. 40 nm) in the variable temperature UV/vis spectra of the disubstituted bis(3,5-di-tert-butylphenyl)porphyrin is indicative of yet higher aggregates involving both 2-aminopyrimidin-5-yl groups. The tetrameric nature of the monosubsituted derivative is confirmed by X-ray analysis, which reveals that two of the 2-aminopyrimidin-5-yl groups are encapsulated by the aggregate and consequently are prevented from undergoing hydrogen bonding. NMR studies show there is no exchange of the 2-aminopyrimidin-5-yl groups, so the tetramer is rigid, which is confirmed by molecular modeling calculations. The tetramer formation is governed by pi-pi interactions, metal coordination, and hydrogen bonding. The di(2-aminopyrimidin-5-yl) derivative forms strongly scattering solutions, which upon standing form green flocculate precipitates, reminiscent of shaken suspensions of bacteriochlorophyll c.
authors.affiliation: Forschungszentrum Karlsruhe, Institute for Nanotechnology, Postfach 3640, D-76021 Karlsruhe, Germany. silviu.balaban@int.fzk.de
authors.forename: Teodor Silviu
authors.initials: TS
authors.lastname: Balaban
authors.forename: Richard
authors.initials: R
authors.lastname: Goddard
authors.forename: Myriam
authors.initials: M
authors.lastname: Linke-Schaetzel
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Lehn
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001429:Bacteriochlorophylls; D040761:Biomimetic Materials / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D011743:Pyrimidines / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D008665:Metalloporphyrins; D011743:Pyrimidines; C012180:2-aminopyrimidine; C017802:zinc hematoporphyrin; C002084:bacteriochlorophyll c; D015032:Zinc