A remarkably strained cyclopyrenylene trimer that undergoes metal-free direct oxygen insertion into the biaryl C–C σ-bond
Synthesis of a remarkably strained cyclopyrenylene trimer CP3 was achieved and it underwent the first metal-free direct oxygen insertion into the biaryl C–C σ-bond. A priori highly-strained CP3 exhibits the longest wavelength emission among whole pyrene-based fluorophores due to the intensive electronic interactions between pyrenes. The color of emission drastically changes from orange to light blue upon oxidation. Theoretical studies revealed that the release of ring strain reasonably drives the reaction between two CP3 molecules and O2. This strain-induced transformation could be also applied for a sulfur atom insertion into the biaryl σ-bond.