A set of four porphyrin trimers (1-4) consisting of an energy-accepting 5,1
5-diphenylethynyl-substituted Zn(II)-porphyrin core flanked by two energy-
donating peripheral Zn(IT)-porphyrins have been prepared as a new efficient
energy-transfer functional unit. The peripheral porphyrin donor is either
a TPP-tppe Zn(II)porphyrin for 1 and 2 or a OEP-type Zn(II)-porphyrin for 3
and 4 and the diphenylethynyl substitution axis of the core porphyrin is a
ligned either orthogonal in 1 and 3 or parallel in 2 and 4 with respect to
the long axis of the trimeric arrays. Femtosecond transient absorption spec
troscopy and femtosecond up-conversion fluorescence measurement have reveal
ed the very efficient S-1-S-1 energy-transfer reactions in these porphyrin
trimers. The S-1-S-1 energy transfer is faster in the parallel trimers 2 an
d 4 than in the orthogonal trimers 1 and 3, reflecting larger electronic co
upling in the former pair. The peripheral porphyrin S-2-state lifetime is c
onsiderably shortened in 1-4, which has been ascribed to S-2-S-2 energy tra
nsfer. Probably the strong Soret-transitions of both the donor and acceptor
lead to large Coulombic interactions, thereby rendering S2-S2 energy trans
fer effective enough to compete with rapid internal conversion to S-1-state
. These results encourage a new strategy for construction of porphyrin-base
d supramolecular artificial photosynthetic antenna.