Coupling of large-amplitude side chain motions to the excited-state H-atom transfer of perylene quinones: Application of theory and experiment to calphostin C

The excited-state intramolecular II-atom transfer reactions of hypocrellins B and A are compared with those of calphostin C. On the basis of the results of transient absorption measurements and ab initio quantum mechanical calculations, it is concluded that large-amplitude conformational changes are coupled to the II-atom transfer in calphostin C,just as they are in hypocrellins A and B. The calculations on this very large molecule with a very complex ground electronic state potential energy surface were made possible by the use of highly scalable electronic structure theory codes on large parallel computers.