Non‐Statistical Assembly of Donor–Acceptor Cages for Light‐Induced Charge Separation

Abstract

Abstract We report light‐triggered charge separation in two discrete supramolecular architectures that self‐assemble in a single step from donor ( D ) and acceptor ( A ) functionalized bridging ligands and Pd(II) cations. The “shape complementary assembly” (SCA) strategy allows for exclusive formation of the cis ‐[Pd 2 D 2 A 2 ] 4+ cage isomer. Compared to previously reported statistical DA assemblies, lacking stoichiometry and stereo control, the number of possible electron transfer routes was reduced. This enables a better understanding and tunability of the excited state dynamics. Cage assembly was investigated by NMR, MS, and single crystal X‐ray diffraction analysis. Steady‐state absorption and electrochemical properties indicate that donor and acceptor moieties remain largely independent in the electronic ground state. Femtosecond pump‐probe spectroscopy in the visible and infrared was applied to compare the fate of photoexcited states for pure ligands, donor‐ and acceptor‐only assemblies, and the donor–acceptor heteroleptic cages. For the latter, ultrafast intracage ligand‐to‐ligand charge separation is followed by two back electron transfer pathways, occurring on timescales of hundreds of picoseconds and around one nanosecond, assignable to D / A ligands facing each other in cis ‐ or trans ‐position. Our work shows that non‐statistical modular self‐assembly can be used for the precise positioning of photoredox‐active components in defined distances on the nanoscale.