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(II)-porphyrins were readily prepared by Cu(I)-catalyzed 1,3-dipolar cycloaddition of benzyl azide to meso-ethynylated Zn(II)-porphyrin (click chemistry). In noncoordinating CHCl(3) solvent, spontaneous assembly occurred to form tetrameric array (3)(2) from meso-meso-linked diporphyrins 3, and dodecameric porphyrin squares (4)(4) and (5)(4) from the L-shaped meso-meso-linked triporphyrins 4 and 5. The structures of these assemblies were examined by (1)H NMR spectra, absorption spectra, and their gel permeation chromatography (GPC) retention time. Furthermore, the structures of the dodecameric porphyrin squares (4)(4) and (5)(4) were probed by small- and wide-angle X-ray scattering (SAXS/WAXS) measurements in solution using a synchrotron source. Excitation-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 8.8 ps(-1) for (5)(4).