Ultrafast Photoinduced Symmetry-Breaking Charge Separation and Electron Sharing in Perylenediimide Molecular Triangles

We report on a visible-light-absorbing chiral molecular triangle composed of three covalently linked 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis- (dicarboximide) (EDT) units. The rigid triangular architecture reduces the electronic coupling between the PDIs, so ultrafast symmetry-breaking charge separation is kinetically favored over intramolecular excimer formation, as revealed by femtosecond transient absorption spectroscopy. Photoexcitation of the PDI triangle dissolved in CH2Cl2 gives PDI+center dot-PDI-center dot in tau(CS) = 12.0 +/- 0.2 ps. Fast subsequent intramolecular electron/hole hopping can equilibrate the six possible energetically degenerate ion-pair states, as suggested by electron paramagnetic resonance/electron nuclear double resonance spectroscopy, which shows that one-electron reduction of the EDT triangle results in complete electron sharing among the three PDIs. Charge recombination of PDI+center dot PDI-center dot to the ground state occurs in tau(CR) = 1.12 +/- 0.01 ns with no evidence of triplet excited state formation.