Denitrogenative Annulation of Benzotriazoyl Porphyrins: Synthesis of Diverse N-Heterocycle-Fused Porphyrinoids with Enhanced NIR Absorption

A diverse range of N-heterocycle-fused porphyrins were efficiently prepared via unprecedented cascade annulation of readily accessible benzotriazolyl-appended porphyrins in diglyme. The present protocol provides metal-free and direct access to structurally diverse N-heterocycle-fused (meso-β, β-β) and carbazolyl-appended porphyrinoids in good yields. In addition, the prepared N-heterocycle-fused porphyrinoids displayed drastic changes in absorption spectra (red-shifted), higher singlet oxygen generation ability (ΦΔ ≈ 0.73), and narrow band gap (∼1.84 eV) and responded to protonation and deprotonation processes to produce a switchable pH-sensitive near-IR chromophore.