Dihedral-angle modulation of meso-meso-linked ZnII diporphyrin through diamine coordination and its application to reversible switching of excitation energy transfer

The dihedral angle between the two porphyrins in meso-meso-linked ZnII diporphyrin can be modulated effectively by adding 1,7-diaminoheptane, which coordinates at the both ZnII centers (see picture). This mechanical torsion gives rise to a decrease in the energy of the S1 state in the meso-meso-linked ZnII-diporphyrin subunit, and results in the change in direction of the energy transfer in the excited state. This process can be reversed by adding acetic acid.