Control of Photodynamics in Supramolecules Containing Metal Complexes by an Unpaired Electron

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A paramagnetic centers perturbs reaction dynamics and photophysical properties of molecular system even via a long distance. Thus by utilizing the paramagnetic species attached in a remote site, it will be possible to control the local dynamics of the molecular system with a long-range interaction.Intersystem crossing is one of the simple photophysical processes, and it is suitable to study effect on the photodynamics by the long-range interaction with unpaired electron. In paramagnetic-metalloporphyrin - free base (diamagnetic) porphyin heterodimers such as a copper-free base porphyrin, the free base half undergoes enhanced intersystem crossing by interaction with the unpaired electron in the other half. Recently we have reported that in a series of copper(II)-free base porphyrin dimer linked via an aromatic spacer, the EISC rate exponentially decreases with the number of bonds of the spacer. In addition, the porphyrin HOMO affects EISC rates itself but does not influence the spacer dependence. This feature is in good agreement with an expression for EISC, derived theoretically.In this project, we examined dependence of the EISC on the paramagnetic species in linearly-linked porphyrin dimers. The paramagnetic porphyrin halves we studied are V(IV)O porphyrins and a radical coordinated zinc(II) porphyrins. Difference of the EISC rate of the free base half between different paramagnetic species does not simply depends on the species itself. The EISC rate depends on the interaction between the unpaired electron and pai system, which is directly connected to the paramagnetic species. Long-range interaction with a remote electron is summarized in terms of three different factors, i.e., spacer, terminal HOMO and interaction between the unpaired electron and direct connecting site.