‘Nonvertical’ triplet energy transfer to a severely non-planar 1,3-diene: proposal of a mechanism based on progressive endothermicity of vertical transfer to individual single-bond torsional levels

The 1,3-diene unit in trans-β-ionol exhibits extreme ‘nonvertical’ behaviour in accepting triplet energy from a series of donors, a result strongly supporting a mechanism herein presented, which depends on the modes of single-bond torsion available to non-planar molecules and the relative dispositions of their So and T1 surfaces with respect to such torsion.