The triplet state of methyl 1,2-diphenylcyclopropene-3-carboxylate

• Published in: Journal of photochemistry 1983-01, Vol.21 (4), p.325-342
• Main Authors: Herkstroeter, William G., Specht, Donald P., Farid, Samir
• Format: Article
• Language: English
• ISSN: 0047-2670
• DOI: 10.1016/0047-2670(83)87118-4

Methyl 1,2-diphenylcyclopropene-3-carboxylate (CP), which is of special interest because of its role as a monomer in photo-cross-linkable polymers, was selected as a representative example of a substituted cyclopropene for investigation of its triplet state. Flash photolysis was used to view the CP triplet directly and to measure the rate constants for energy transfer to CP from a series of triplet sensitizers. Because the intersystem crossing quantum yield of CP is only 5 × 10 −3, the triplet state can be populated efficiently only by energy transfer from an appropriate sensitizer. In benzene solution the triplet lifetime of CP is 360 μs, and the rate constant for reaction with ground state CP to form dimers is 3.8 × 10 7 M −1 s −1. The 0—0 energy of the triplet state is 51.0 kcal mol −1 (17.8 kilokaysers), determined from a plot of the energy transfer data according to the Balzani equation. The profile of this plot shows that the ground and triplet state geometries of CP are different, probably because of partial relief in the triplet state of the considerable ground state strain energy.