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

Abstract

Conveniently modified polycyclic aromatic hydrocarbon (PAH) fluorophores are obtained by a bromination-borylation sequence. The bis-borylated dyes show red-shifted absorption (lambda(abs,max) > 450 nm) and emission (lambda(f,max) > 500 nm; phi(f): 0.3-0.5) properties as compared to the parent PAHs. Their centrosymmetric A-pi-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 (phi(Delta): 0.50-0.66). This bipartition provides the setting for the concomitant observation of fluorescence and photosensitization, making these dyes ideal bimodal chromophores.