Transition-Metal Isocorroles as Singlet Oxygen Sensitizers

Building on a highly efficient synthesis of pyrrole-appended isocorroles, we have worked out conditions for manganese, palladium, and platinum insertion into free-base 5/10-(2-pyrrolyl)-5,10,15-tris(4-methylphenyl)isocorrole, H2[5/10-(2-py)TpMePiC]. Platinum insertion proved exceedingly challenging but was finally accomplished with cis-Pt(PhCN)2Cl2. All the complexes proved weakly phosphorescent in the near-infrared under ambient conditions, with a maximum phosphorescence quantum yield of 0.1% observed for Pd[5-(2-py)TpMePiC]. The emission maximum was found to exhibit a strong metal ion dependence for the 5-regioisomeric complexes but not for the 10-regioisomers. Despite the low phosphorescence quantum yields, all the complexes were found to sensitize singlet oxygen formation with moderate to good efficiency, with singlet oxygen quantum yields ranging over 21-52%. With significant absorption in the near-infrared and good singlet oxygen-sensitizing ability, metalloisocorroles deserve examination as photosensitizers in the photodynamic therapy of cancer and other diseases.

Automated summary

Based on a highly efficient synthesis method, platinum insertion into pyrrole-appended isocorroles has been accomplished, despite the initial difficulties. The complexes showed weak phosphorescence but exhibited good singlet oxygen-sensitizing ability. With their unique properties, metalloisocorroles are worth further investigation as photosensitizers in the photodynamic therapy of diseases.