Determining Factor of the Quantum Yield of the Cyclization Reaction via Triplet States for Dye-Attached Diarylethene

The difference in the quantum yields of the cyclization reaction of two isomers of dye-attached diarylethene via the triplet state observed in the experiment [J. Phys. Chem. C 2009, 113, 11623-11627] was theoretically examined by quantum chemical calculations. By evaluating the spin-orbit couplings, we found that the ratio of the rate constants from the S₁ state to the T₂ state between two isomers agreed with that of the experimental quantum yield of the cyclization reaction. The difference in the spin-orbit couplings is due to the difference in the delocalization of the orbitals between diarylethene and dye. We further found that after the intersystem crossing took place the cyclization reaction via the triplet state occurred in the experiment due to the low energy barrier (∼10 kcal/mol) for the reaction.