Quantum Chain Reaction of Tethered Diarylcyclopropenones in the Solid State and Their Distance-Dependence in Solution Reveal a Dexter S₂–S₂ Energy-Transfer Mechanism

When promoted to their second singlet excited state (S₂) in benzene, alkyl-linked dimers of diarylcyclopropenone undergo a photodecarbonylation reaction with quantum yields varying from Φ = 0.7 to 1.14. Quantum yields greater than 1.0 in solution rely on an adiabatic reaction along the S₂ energy surface where the immediately formed excited-state product transfers energy to the unreacted molecule in the dimer to generate a second excited state. By determination of the quantum yields of decarbonylation for the linked diarylcyclopropenones with linkers of various lengths it was shown that S₂ → S₂ energy transfer is limited to distances shorter than ca. 6 Å. Notably, the quantum chain reaction occurs with similar efficiency for all the linked diarylcyclopropenones dimers in the solid state