Large porphyrin squares from the self-assembly of meso-Triazole-Appended L-Shaped meso-meso-Linked Zn^II-Triporphyrins: synthesis and efficient energy transfer

meso-Triazolyl-appended Zn^IIporphyrins were readily prepared by Cu^I-catalyzed 1, 3-dipolar cycloaddi-tion of benzyl azide to meso-ethynylat-ed Zn^II-porphyrin (click chemistry). In noncoordinating CHCl₃ solvent, spon-taneous assembly occurred to form tet-rameric array (3)₂: from meso-meso-linked diporphyrins 3 ₁ and dodecameric porphyrin squares (4)₄ and (5) ₄ from the L-shaped meso-meso-linked tripor-phyrins 4 and 5. The structures of these assemblies were examined by ¹H NMR spectra, absorption spectra, and their gel permeation chromatography (GPC) retention time. Furthermore, the struc-tures of the dodecameric porphyrin squares (4) ₄ and (5)₄ were probed by small- and wide-angle X-ray scattering (SAXS/WAXS) measurements in solu-tion using a synchrotron source. Excita-tion-energy migration processes in these assemblies were also investigated in detail by using both steady-state and time-resolved spectroscopic methods, which revealed efficient excited-energy transfer (EET) between the meso-meso-linked Zn^II-porphyrin units that occurred with time constants of 1.5 ps^-1 for(3)₂ and 8.8ps^-1 for (5)₄.