Superexchange mediated energy transfer in zinc(II) porphyrin-free base porphyrin dimers: comparison of m- and p-bis(phenylethynyl) phenylene linked dimers.

The singlet-singlet energy transfer rate in a new zinc(II) porphyrin-free base porphyrin dimer, having a m-bis(phenylethynyl)phenylene bridge, was found to be slower than that in the corresponding p-bis(phenylethynyl)phenylene-bridged dimer, despite the shorter donor-acceptor distance and pathway. The slower rate is interpreted as evidence for a major contribution of the superexchange mechanism.