Isomerization reactions with [Ru(Bpy)3]2+ photocatalyst. A DFT study of the factors influencing the energy transfer mechanism supported by experimental data

The combination of experimental data and computational calculations has become a powerful method to understand and predict reactivity of many physicochemical processes. This work focused on alkene photoisomerization reactions, where the thermodynamically less stable product can be obtained. We performed photoisomerization reactions with various alkenes using tris(2,2?-bipyridine)ruthenium(II) ([Ru(Bpy)3]2+) as photocatalyst and the reaction mechanisms were studied by DFT calculations. Results showed that the lightpromoted conversion of trans-stilbene to the cis-isomer proceeds with a 94 % conversion, exhibiting a first order rate with respect to the concentration of trans-stilbene and with a rate constant of 1.6 ? 10-4 s-1. Computational data showed the trans-species to be thermodynamically favored. However, the transition from singlet to triplet excited state for the trans-isomer has an estimated value of 5.6 kcal/mol lower in energy than the cis-isomer. This energy difference allows the trans-isomer to be activated by the Ru-photocatalyst, while the cis one remains unreactive. When the singlet to triplet energy requirement for the alkene is higher than that of the photocatalyst, no reaction occurs. Results support an energy transfer (EnT) mechanism and illustrate the photocatalyst energy requirements to perform isomerization reactions.

Automated summary

The study focused on alkene photoisomerization reactions using experimental data and computational calculations. Results showed that the trans-species can be converted to the cis-isomer with a high conversion rate due to energy transfer mechanism. This highlights the importance of understanding the energy requirements of the photocatalyst in isomerization reactions.