Exploring the Azabenzannulation on Benzothioxanthene Imide

We report herein the synthesis and characterization of azabenzannulated benzothioxanthene imides (BTIs) functionalized with various appended aromatic units. This new class of polycyclic aromatic hydrocarbons are prepared via a straightforward and efficient synthetic strategy that involves a visible-light-mediated photocyclization of imines. The later are formed in situ from the condensation of an amine moiety at the bay position of the BTI core with aldehydes, followed by oxidative rearomatization. These green-yellow fluorescent emitters (φf ~ 0.14-0.20) combine dual redox properties with significant triplet state generation — resulting from a combination strong spin-orbit couplings and the energetic proximity between their S1 state and their triplet states — with singlet oxygen sensitization efficiencies φΔ~ 0.39-0.49. Hence, this design principle enables accessible tailored structural modifications through the incorporation of diverse functional groups onto the BTI core with minimal synthetic effort, paving the way to original and versatile functional materials with broad potential in optoelectronics, biophotonics, and photodynamic therapy.