Ultrafast excited-state relaxation process has been studied with zinc porphyrin dimers and circular trimer. Following 80 fs excitation at Soret band (420 nm) or Q band (580 nm) of zinc porphyrin, the fluorescence decay curves exhibit ultrafast decays with lifetimes of 80 fs in o-dimer, 450 fs in trimer and 540 fs in m-dimer. The timeresolved fluorescence spectra show that the fast decay process correspond to disappearance of monomer-like emission followed by red-shifted and broaden spectra. These ultrafast processes are assigned as due to excitation transfer among monomers and delocalization of excitation yielding excitonic states.
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