Spin-selective triplet energy transfer from C60 to 1,3,5-phenylene-based dendritic metal-free porphyrin

Excited-state dynamics of 1,3,5-phenylene-based dendritic metal-free porphyrin (H2DP), which can include one C60 molecule, has been investigated by time-resolved electron paramagnetic resonance (TREPR). The TREPR signal of H2DP-C60 system is attributed to the lowest excited triplet (T1) state of the H2DP moiety, since the zero-field splitting is similar to pristine H2DP. However, the electron spin polarization (ESP) of H2DP-C60 is opposite to that of pristine H2DP, evidently indicating the inclusion effect. This ESP inversion is interpreted by spin-selective triplet energy transfer process from C60 to H2DP, from which it is determined that the fine structure z axis of C60 is perpendicular to that of H2DP. This study is useful for understanding the excited-state dynamics of porphyrin–fullerene dyads.