Quantum Chain Reaction Of Tethered Diarylcyclopropenones In The Solid State And Their Distance-Dependence In Solution Reveal A Dexter S-2-S-2 Energy-Transfer Mechanism

When promoted to their second singlet excited state (S-2) in benzene, alkyl-linked dimers of diarylcyclopropenone undergo a photodecarbonylation reaction with quantum yields varying from Phi = 0.7 to 1.14. Quantum yields greater than 1.0 in solution rely on an adiabatic reaction along the S-2 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 S-2 -> S-2 energy transfer is limited to distances shorter than ca. 6 A. Notably, the quantum chain reaction occurs with similar efficiency for all the linked diarylcyclopropenones dimers in the solid state.