Bis-borylated arylisoquinoline-derived dyes with a central aromatic core: towards efficient fluorescent singlet-oxygen photosensitizers

Conveniently modified polycyclic aromatic hydrocarbon (PAH) fluorophores are obtained by a bromination–borylation sequence. The bis-borylated dyes show red-shifted absorption ( λ abs,max > 450 nm) and emission ( λ f,max > 500 nm; Φ f : 0.3–0.5) properties as compared to the parent PAHs. Their centrosymmetric A–π-A (A: acceptor) structures led to the observation of two-photon absorption (up to 60 GM) in the near-infrared spectral region (>800 nm). The rigid structure shuts down non-radiative deactivation by limiting rotational or vibrational freedom. Thus, the excited-state pathways originating from the excited singlet state are resumed to fluorescence and excited triplet-state formation. The latter is involved in the energy-transfer sensitization of singlet oxygen ( Φ Δ : 0.50–0.66). This bipartition provides the setting for the concomitant observation of fluorescence and photosensitization, making these dyes ideal bimodal chromophores.