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 .