Intramolecular B←N Lewis pair functionalization of polycyclic aromatic hydrocarbons (PAHs) is emerging as a powerful strategy for tailoring their optical and electronic properties to specific applications. Herein, we report the design and synthesis of four quadrupolar pyrene fluorophores containing triarylamine donor and pyridyl-borane acceptor substituents by N-directed electrophilic C-H borylation in the K-region. Introduction of rigid six-membered B-N heterocycles greatly decreased the lowest unoccupied molecular orbital (LUMO) energy levels and red-shifted the absorption and emission maxima compared to the nonborylated precursors. These pyrenes exhibit absorptions spanning the entire visible region and intense green to deep red and near-infrared fluorescence, with impressive quantum yields as high as 82%. The simultaneous presence of pyridyl-borane acceptor and arylamine donor units also enables facile reversible multiredox oxidation and reduction processes. The advantageous photophysical and electrochemical characteristics are highly attractive for optoelectronic devices and (bio)imaging applications. The pyrene derivative with the most red-shifted emission, 5-Pf, was further evaluated in live cell imaging studies, showing effective staining of acidic compartments, including lysosomes. In addition, we demonstrate the outstanding performance of 5-Pf as a novel electrochemiluminescent (ECL) luminophore through annihilation and coreactant experiments in cyclic voltammetry and pulsing modes. Spooling ECL spectroscopy revealed a strong emission with a maximum at 646 nm, in good agreement with the photoinduced emission maximum at 660 nm. A superior absolute ECL efficiency (ΦECL) of up to 0.9 ± 0.1%, exceeding that of typically employed Ru(bpy)32+, was achieved during CV scanning with benzoyl peroxide as a coreactant.
Vanga et al. (Mon,) studied this question.
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