Fast transient absorption spectroscopy of the early events in photoexcited chiral benzophenone–naphthalene dyads

Photoinduced intra-molecular energy transfer in two ketoprofen(KP)-naproxol(NPX) diastereomers proceeds via two pathways. Very fast singlet–triplet energy transfer (k = 1.2 × 1011 s−1) from KP to NPX occurs for a small percentage (6%) and the major pathway is triplet–triplet energy transfer (k ∼ 3 × 109 s−1). This was shown with femtosecond transient absorption spectroscopy and global and target analysis. Whereas the NPX triplet decay is strongly stereospecific (ratio of 1.6), the NPX triplet state formation for both dyads is very similar (ratio of 1 for the fast process and 1.2 for the slower process).