Exploring the Azabenzannulation of Benzothioxanthene Imide

Abstract

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 is prepared via a straightforward and efficient synthetic strategy that involves a visible-light-mediated photocyclization of imines. The latter 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 (φ_f ∼ 0.14-0.20) combine dual redox properties with significant triplet state generation─resulting from a combination of strong spin-orbit coupling and the energetic proximity between their S₁ and triplet states─with notable singlet oxygen sensitization efficiencies (φ_Δ ∼ 0.39-0.49). Hence, this design principle enables accessible, tailored structural modifications through the incorporation of diverse functional groups into 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.