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.