Aromatic-bridged and Meso-Meso-linked BF2-smaragdyrin Dimers Exhibit Fast Decays in Polar Solvents by Symmetry-Breaking Charge Transfer

Symmetry-breaking charge transfer is one of the key process in photosynthetic reaction centers and specific artificial optoelectronic devices such as dye-sensitized solar cells. Here we report the synthesis of aromatic-bridged BF 2 -smaragdyrin dimers, meso -free BF 2 -smaragdyrin, and its meso - meso -linked BF 2 -smaragdyrin dimer. The decays of S 1 -states of these dimers are accelerated with an increase in solvent polarity and a decrease in the distance between the two BF 2 -smaragdyrin units, suggesting symmetry-breaking charge transfer. The fluorescence lifetimes of the dimers become shortened in polar solvents. However, ultrafast transient absorption spectroscopy do not detect charge-separated ion pairs. On the basis of these results, we conclude that the decays of the excited states of the BF 2 -smaragdyrin dimers are accelerated by solvation-induced symmetry-breaking charge transfer, depending on the degree of the electronic interaction between the smaragdryin units as a rare case for porphyrinoids. The degree of charge transfer is larger for dimers with larger electronic interactions.