Serendipitous Discovery of Conjugated Dipyrromethene-Linked Nitronaphthoporphyrins

Acid-catalyzed condensation of a nitronaphthalene-fused dipyrrylmethane with dipyrrylmethane dialdehydes afforded unique dipyrromethene-naphthoporphyrin conjugates together with expected nitronaphthoporphyrins. The unusual conjugated system retained aromatic porphyrin-type characteristics but afforded highly modified UV-vis spectra with multiple absorptions throughout the visible region.

Stable Dication Diradicals of Triply Fused Metallo Chlorin-Porphyrin Heterodimers: Impact of the Bridge on the Control of Spin Coupling to Reactivity

We report an unexpected rearrangement, controlled by the nature of the bridge, leading to the formation of novel, remarkably stable triply fused dinickel(II)/dicopper(II) chlorin-porphyrin dication diradical heterodimers in excellent yields. Here, a dipyrromethene bridge gets completely fused between two porphyrin macrocycles with two new C-C and one C-N bonds. The two macrocycles exhibit extensive π-conjugation through the bridge, which results in an antiferromagnetic coupling between the two π-cation radicals. In addition, the macrocyclic distortion also favours a rare intramolecular ferromagnetic interaction between the CuII and π-cation radical spins to form a triplet state. The structural and electronic perturbation in the unconjugated dication diradical possibly enables the bridging pyrrolic nitrogen to undergo a nucleophilic attack at the nearby β-carbon of the porphyrin π-cation radical with a computed free energy barrier of >20 kcal mol-1 which was supplied in the form of reflux condition to initiate such a rearrangement process. UV-vis, EPR and ESI-MS spectroscopies were used to monitor the rearrangement process in situ in order to identify the key reactive intermediates leading to such an unusual transformation.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications

The use of boron dipyrromethene (BODIPY) in biomedicine is reviewed. To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

Long-Range Intramolecular Spin Coupling through a Redox-Active Bridge upon Stepwise Oxidations: Control and Effect of Metal Ions

Dinickel(II) and dicopper(II) porphyrin dimers have been constructed in which two metalloporphyrin units are widely separated by a long unconjugated dipyrrole bridge. Two macrocycles are aligned somewhat orthogonally to each other, while oxidation of the bridge generates a fully π-conjugated butterfly-like structure, which, in turn, upon stepwise oxidations by stronger oxidants result in the formation of the corresponding one- and two-electron-oxidized species exhibiting unusual long-range charge/radical delocalization to produce intense absorptions in the near-infrared (NIR) region and electron paramagnetic resonance (EPR) signals of a triplet state due to interaction between the unpaired spins on the Cu(II) ions. Although the two metal centers have a large physical separation through the bridge (more than 16 Å), they share electrons efficiently between them, behaving as a single unit rather than two independent centers. Detailed UV-vis-NIR, electrospray ionization mass spectrometry, IR, variable-temperature magnetic study, and EPR spectroscopic investigations along with X-ray structure determination of unconjugated, conjugated, and one electron-oxidized complexes have been exploited to demonstrate the long-range electronic communication through the bridge. The experimental observations are also supported by density functional theory (DFT) and time-dependent DFT calculations. The present study highlights the crucial roles played by a redox-active bridge and metal in controlling the long-range electronic communication.

Rhodium-catalyzed annulation of pyrrole substituted BODIPYs with alkynes to access π-extended polycyclic heteroaromatic molecules and NIR absorption

A series of π-extended BODIPY derivatives fused with an indolizine scaffold were prepared smoothly via rhodium-catalyzed C–H functionalization/annulation. These fluorophores show significantly red-shifted absorption, reaching to the near infrared (NIR) region.

Benzene- and pyridine-incorporated octaphyrins with different coordination modes toward two PdII centers

Expanded porphyrins have received considerable attention due to their unique optical, electrochemical and coordination properties. Here, we report benzene- and pyridine-incorporated octaphyrins(1.1.0.0.1.1.0.0), which are synthesized through Suzuki-Miyaura coupling of α,α'-diboryltripyrrane with m-dibromobenzene and 2,6-dibromopyridine, respectively, and subsequent oxidation with 2,3-dicyano-5,6-dichlorobenzoquinone. Both octaphyrins are nonaromatic and take on dumbbell structures. Upon treatment with Pd(OOCCH₃)₂, the benzene-incorporated one gives a C_i symmetric NNNC coordinated bis-Pd^II complex but the pyridine incorporated one gives C_i and C_s symmetric NNNC coordinated bis-Pd^II complexes along with an NNNN coordinated bis-Pd^II complex bearing a transannular C-C bond between the pyrrole α-positions. In addition, these two pyridine-containing NNNC Pd^II complexes undergo trifluoroacetic acid-induced clean interconversion.

Conjugated BODIPY Oligomers with Controllable Near-Infrared Absorptions as Promising Phototheranostic Agents through Excited-State Intramolecular Rotations

Conjugated molecules with coplanar strong donor and acceptor (D-A) units have been widely used in the design of near-infrared (NIR) photothermal agents to increase an absorption band through intramolecular charge transfer and to control intramolecular motions in aggregated states. However, such conjugated D-A systems have strong dipolar moments and intermolecular interactions, which may inhibit other channels of photothermal conversion and are often susceptible to nucleophiles, especially in the presence of light irradiation. Now, we report a molecular guideline to develop novel NIR organic photothermal nanoagents based on conjugated boron dipyrromethene (BODIPY) oligomers. This oligomerization is helpful not only for their tunable NIR absorptions in the ground state with distinctly redshifted absorption maxima up to 1002 nm and high extinction coefficients but also for their highly efficient photothermal conversion because of the possible motion of the BODIPY motifs around the ethene linked group in the excited state. These oligomers were fabricated as ultra-photostable nanoagents for multiple imaging-guided phototherapies, which efficiently accumulated in tumors, and gave complete tumor ablation with NIR laser irradiation. This strategy of "ground-state conjugation, excited-state rotation" provides a novel guideline to develop advanced theranostic molecules with NIR absorption.

Strategic Construction of Ethene-Bridged BODIPY Arrays with Absorption Bands Reaching the Near-Infrared II Region

An efficient strategy for the controllable synthesis of BODIPY arrays based on the Stille cross-coupling reaction has been developed, from which a family of well-defined ethene-bridged BODIPY arrays from dimer to hexamer was synthesized. These arrays showed strong absorptions reaching the near-infrared II (NIR II, 1000-1700 nm) region with maxima tunable from 702 nm (dimer) to 1114 nm (hexamer) and possessed efficient light-harvesting capabilities, excellent photostability, and good photothermal conversion abilities under NIR light irradiation.

Porphyrin-Ryleneimide Hybrids: Low-Bandgap Acceptors in Energy-Transfer Cassettes

Energy-transfer cassettes consisting of naphthaleneimide-fused metalloporphyrin acceptors (M=Zn and Pd) and BODIPY donors have been designed and synthesized. These systems have rigid pseudo-tetrahedral structures with a donor-acceptor separation of ca. 17.5 Å. Spectroscopic investigations, including femtosecond transient absorption measurements, showed efficient excitation energy transfer (EET) occurring according to the Förster mechanism. Strong fluorescence of the donor units and significant spectral overlap of the donor and acceptor subunits are prerequisites for the efficient EET in these systems.

Atropisomers of meso Tetra(N-Mesyl Pyrrol-2-yl) Porphyrins: Synthesis, Isolation and Characterization of All-Pyrrolic Porphyrins

Atropisomerism has been observed in a variety of biaryl compounds and meso-aryl substituted porphyrins. However, in porphyrins, this phenomenon had been shown only with o-substituted 6-membered aromatic groups at the meso-position. We show herein that a 5-membered heteroaromatic (N-mesyl-pyrrol-2-yl) group at the meso-position leads to atropisomerism. In addition, we report a 'one-pot' synthetic route for the synthesis of 'all-pyrrolic' porphyrin (APP) with several N-protection groups (Boc, Cbz, Ms and Ts). Among these groups, we found that only the Ms group gave four individually separable atropisomers of meso-tetra(N-Ms-pyrrol-2-yl) porphyrin. Furthermore, the reductive removal of Cbz- was achieved to obtain meso-tetra(pyrrol-2-yl) porphyrin. Thus, our synthetic procedure provides an easy access to a group of APPs and stable atropisomers, which is expected to expand the application of novel APP-based materials.

Carbazole-containing porphyrinoid and its oligomers

A novel carbazole-containing porphyrinoid 4H and its oligomers 6H and 7H were synthesized for the first time via the Suzuki-Miyaura cross-coupling reaction. The structures of 4H, 4Pd, 6H, and 6Zn were finally confirmed by X-ray analysis. The exciton coupling strength (628 cm^-1) in 4Zn, 6Zn, and 7Zn was found to be larger than that of the directly-linked porphyrin arrays (570 cm^-1), extending their absorption spectra to the NIR region as well as enhancing the extinction coefficients.

Synthesis of a doubly SO2-fused phlorin: Tuning the structure and properties by the SO2 groups

A doubly SO2-fused phlorin 4 has been synthesized by the [2 + 2] condensation of dipyrromethanecarbinol 2 and SO2-fused dipyrromenthane 3 in the presence of TFA, followed by DDQ oxidation. The SO2-fused phlorin 4 has been characterized by absorption, fluorescence, mass and NMR spectra, as well as X-ray analysis. Compared to the [Formula: see text]-unsubstituted phlorin 5, the SO2-fused phlorin 4 exhibits a red-shifted absorption spectrum (around 12 nm), a more distorted molecular conformation, as well as nice photostability even with an electron-donating meso-3,5-di-tert-butylphenyl group. The titration of 4 and 5 with TBAF has been monitored by absorption spectroscopy. The deprotonated phlorin 4 shows a peak at 870 nm which is red shifted by 26 nm compared to that of deprotonated 5.