Fully Conjugated Pyrene-BODIPY and Pyrene-BODIPY-Ferrocene Dyads and Triads: Synthesis, Characterization, and Selective Noncovalent Interactions with Nanocarbon Materials

Optoelectronic Properties and Fluorescence Lifetime Imaging Application of Donor-Acceptor Dyads Derived From 2,6-DicarboxyBODIPY

Donor-acceptor BODIPY dyads, functionalized at the 2 and 6 positions with benzyl ester (BDP-DE) or carboxylic acid (BDP-DA) groups, were synthesized, and their optoelectronic properties were investigated. Carbonyl groups were found to increase the reduction potential of the BODIPY core by 0.15-0.4 eV compared to regular alkyl-substituted BODIPYs. These compounds exhibited efficient intramolecular charge separation and triplet state formation through the spin-orbit charge transfer intersystem crossing (SOCT-ISC) process, achieving singlet oxygen quantum yields of up to 92 %, depending on the solvent polarity. Notably, the fluorescence and singlet oxygen generation of BDP-DAs were found to depend on the ionization state of the carboxylic groups. Time-resolved fluorescence measurements revealed that complexation of BDP-DAs with bovine serum albumine (BSA) significantly extended their excited state lifetimes. Fluorescence lifetime imaging microscopy (FLIM) studies of human colorectal carcinoma (HCT116) cells and pig small intestinal organoids (enteroids) provided insights into subcellular localization. The diacid with 2,4-dimethoxyphenyl group at the meso-position (DA1) displayed longer lifetimes in lipid-droplet-like structures and shorter lifetimes in cytoplasmic regions. The diacid containing a meso-anthracenyl group (DA2) formed 'islands' in cell monolayers, exhibiting a distinct lifetime gradient from the periphery to the center. These results highlight the potential of donor-acceptor BODIPYs as fluorescent probes for biological imaging, particularly in revealing subtle differences in cellular environments.

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 TPPF20Zn (TPPF20Zn = 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 TPPF20Zn were studied by the density functional theory (DFT) and time-dependent DFT (TDDFT). The HOMO and HOMO - 1 of supramolecular complexes TPPF20Zn-7/8 are TPPF20Zn centered, while the LUMO is localized on the BOPHY entity, allowing potential HOMO → LUMO charge transfer from the TPPF20Zn donor to the BOPHY acceptor.

Introducing of an Unexplored Aza-BODIPY Diradicaloids with 4-(2,6-Ditert-butyl)phenoxyl Radicals Located in 1,7-Positions of the Aza-BODIPY Core

We have prepared and characterized two diradicaloid systems 5a and 5b that originated from the oxidation of a 1,7-(4-(2,6-di-tert-butyl)phenol)-substituted aza-BODIPY core. The aza-BODIPY diradicaloids were characterized by a large array of experimental and computational methods. The diamagnetic closed-shell state was postulated as the ground state in solution and a solid-state with the substantial thermal population originating from both open-shell diradical and open-shell triplet states observed at room temperature. Transient absorption spectroscopy indicates fast (<10 ps) excited state deactivation pathways associated with the target compounds' diradical character in solution at room temperature. Variable-temperature 1H NMR spectra indicate the solvent dependency of the diradical character in 5a and 5b. The diradicaloids could be stepwise reduced to the mixed-valence radical-anion and dianion states upon consequent single-electron reductions. Similarly, deprotonated 1,7-(4-(2,6-di-tert-butyl)phenol)-substituted aza-BODIPYs can be oxidized to the diradicaloid form. Both mixed-valence and dianionic forms exhibit an intense absorption in the NIR region. Density functional theory (DFT) and time-dependent DFT calculations were used to explain the transformations in the UV-Vis-NIR spectra of all target compounds.

Anion Sensing through Redox-Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts

Anion sensing via either optical or electrochemical readouts has separately received enormous attention, however, a judicious combination of the advantages of both modalities remains unexplored. Toward this goal, we herein disclose a series of novel, redox-active, fluorescent, halogen bonding (XB) and hydrogen bonding (HB) BODIPY-based anion sensors, wherein the introduction of a ferrocene motif induces remarkable changes in the fluorescence response. Extensive fluorescence anion titration, lifetime and electrochemical studies reveal anion binding-induced emission modulation through intramolecular photoinduced electron transfer (PET), the magnitude of which is dependent on the nature of both the XB/HB donor and anion. Impressively, the XB sensor outperformed its HB congener in terms of anion binding strength and fluorescence switching magnitude, displaying significant fluorescence turn-OFF upon anion binding. In contrast, redox-inactive control receptors display a turn-ON response, highlighting the pronounced impact of the introduction of the redox-active ferrocene on the optical sensing performance. Additionally, the redox-active ferrocene motif also serves as an electrochemical reporter group, enabling voltammetric anion sensing in competitive solvents. The combined advantages of both sensing modalities were further exploited in a novel, proof-of-principle, fluorescence spectroelectrochemical anion sensing approach, enabling simultaneous and sensitive read out of optical and electrochemical responses in multiple oxidation states and at very low receptor concentration.