Introducing Pyridone[α]-Fused BOPHYs as Red-Shifted Bright Fluorophore Potentially Useful as Non-fullerene Acceptors in Donor–Acceptor Dyads

A series of 2-pyridone[α]-fused BOPHYs 6–8 were prepared via a two-step procedure involving the preparation of enamine, followed by an intramolecular heterocyclization reaction. In addition to being fully conjugated with the BOPHY core pyridone fragment, BOPHYs 7 and 8 have a pyridine group connected to the BOPHY core via one- or two –CH₂– groups. New BOPHYs were characterized by spectroscopy as well as X-ray diffraction. Conjugation of the pyridone fragment into the BOPHY core results in a significant red shift of the absorption and fluorescence while maintaining extremely high fluorescence quantum yields. Axial coordination and photophysical properties of the supramolecular dyads formed between pyridine-appended pyridone-fused BOPHYs 7 and 8 with TPP^F20Zn (TPP^F20Zn = zinc 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) were investigated using UV–vis and fluorescence spectroscopy and gave a binding constant in the range of 1.46 × 10⁵ to 4.6 × 10⁵ M^–1. The electronic structures and excited-state properties of new BOPHYs 6–8 and their donor–acceptor assemblies with TPP^F20Zn were studied by the density functional theory (DFT) and time-dependent DFT (TDDFT). The HOMO and HOMO – 1 of supramolecular complexes TPP^F20Zn-7/8 are TPP^F20Zn centered, while the LUMO is localized on the BOPHY entity, allowing potential HOMO → LUMO charge transfer from the TPP^F20Zn donor to the BOPHY acceptor.