Tetrameric and Hexameric Porphyrin Nanorings: Template Synthesis and Photophysical Properties

Hexameric and tetrameric porphyrin nanorings, Z6 center dot T6 and Z4 center dot T4, were synthesized in 53% and 14% yields, respectively, by the Sonogashira-type self-oligomerization of porphyrin monomer 1 using hexadentate template T6 and tetrapyridylporphyrin template T4. Template-free nanorings Z6 and Z4 were also prepared. The femtosecond transient absorption measurements revealed fast excitation energy hopping (EEH) along these nanorings with hopping rates of 2-5 ps. Treatment of Z6 with chiral template CT6 gave Z6 center dot CT6 showing circular dichroism (CD) and circularly polarized luminescence (CPL) in the absorption and fluorescence regions of Z6, respectively, which indicates chirality transfer from CT6 to Z6.