A core-expanded subphthalocyanine analogue with a significantly distorted conjugated surface and unprecedented properties

Bulking Up the Bay-Position Substituents Enables Enhanced Selectivity of Cs-Symmetric Boron Subphthalocyanine-Subnaphthalocyanine Hybrids

The precise synthesis of subporphyrinoid hybrids with π-expanded topologies and unique material properties plays a promising role in the design of functional macrocycles. Easy, selective, and controllable routes to boron subphthalocyanine-subnaphthalocyanine hybrids, Bsub(Pc3-p-Ncp)s, are desirable for this purpose yet synthetically challenging due to random mixtures of Cs-, C3v-, and, in some cases, C1-symmetric compounds that form during traditional statistical mixed cyclotrimerizations. Herein, we addressed this issue by developing a sterically driven mixed cyclotrimerization with enhanced selectivity for the targeted Cs-symmetric hybrid and complete suppression of sterically crowded macrocyclic byproducts. This process, coupled with a rationally designed precursor bearing bulky phenyl substituents, enabled the synthesis and characterization of bay-position phenylated Ph2-(Rp)8Bsub(Pc2-Nc1) hybrids with halogens (Rp = Cl or F) in their peripheral isoindole rings. Reaction selectivity ranged between 59 and 72% with remarkable yields, significantly higher than that of conventional mixed cyclotrimerizations. These findings were augmented by theoretical calculations on precursor Lewis basicity as guiding principles into hybrid macrocycle formation. Additionally, the incorporation of unfused phenyl groups and halogen atoms into the hybrid framework resulted in fine-tuned optical, structural, electronic, and electrochemical properties. This straightforward approach achieved improved selectivity and controlled narrowing of the product distribution, affording the efficient synthesis of structurally sophisticated Bsub(Pc2-Nc1) hybrids. This then expands the library of 3-dimensional π-extended macrocycles for use in a range of applications, such as in optoelectronic devices with precisely tailored optical properties.

Synthesis, Optical Properties, and Fluorescence Cell Imaging of Novel Mixed Fluorinated Subphthalocyanines

Subphthalocyanines (SubPcs) are a kind of tripyrrolic macrocycle with a boron atom at their core. Incorporating different units onto the SubPc periphery can endow them with various unique properties. Herein, a series of novel fluorinated low-symmetry SubPc derivatives containing chlorine groups (F₈-Cl₄-SubPc, F₄-Cl₈-SubPc) and methoxy groups (F₈-(OCH₃)₂-SubPc) were synthesized and characterized by spectral methods (MS, FT-IR, ¹H, ¹³C, ¹¹B, and ¹⁹F NMR spectroscopy), and the effect of the peripheral substituents on their electronic structure of low-symmetry macrocycle was investigated by cyclic voltammetry, theoretical calculation, electronic absorption, and emission spectroscopy. In contrast to perfluorinated SubPcs, these low-symmetry SubPcs revealed non-degenerate LUMO and LUMO + 1 orbitals, especially F₈-(OCH₃)₂-SubPc, which was consistent with the split Q-band absorptions. The cyclic voltammetry revealed that these SubPcs exhibited two or three reduction waves and one oxidation wave, which is consistent with the reported SubPcs. Finally, an intracellular fluorescence imaging study of these compounds revealed that these compounds could enter cancer cells and be entrapped in the lysosomes, which provides a possibility of future applications in lysosome fluorescence imaging and targeting.

Recent advances in subphthalocyanines and related subporphyrinoids

Subporphyrinoids constitute a class of extremely versatile and attractive compounds. Herein, a comprehensive review of the most recent advances in the fundamentals and applications of these cone-shaped aromatic macrocycles is presented.

Periphery-Fused Chiral A2B-Type Subporphyrin

Despite significant interest, the chiroptical properties of subporphyrins have rarely been investigated because chiral subporphyrins are elusive. Here, inherently chiral subporphyrins are elaborated by forming a fused pyran ring at the periphery of an A₂B-type meso-aryl-substituted subporphyrin. Their circular dichroism (CD) properties are largely affected by the peripheral substituents and the dihedral angles between the meso-aryl substituents and the subporphyrin core: the β-perbromo subporphyrin with an orthogonal arrangement of the meso-phenyl substituents to the subporphyrin core exhibits weak CD signals corresponding to the Q bands, whereas the unsubstituted species with smaller dihedral angles shows relatively intense CD signals. A detailed structure–property relationship of these chiral subporphyrins was elucidated by time-dependent (TD) DFT calculations. This study reveals that the CD properties of chiral subporphyrins can be controlled by peripheral substitution and meso-aryl substituents.

Polar columnar assemblies of subphthalocyanines

In this small review article, we provide an overview of the different self-assembled systems and materials created so far by rationally organizing fluorosubphthalocyanines in a non-centrosymmetric fashion, which allows access to novel polarly ordered liquid crystalline materials that can be aligned in the presence of electric fields and that exhibit permanent or switchable ([Formula: see text] ferroelectric) polarization.

Bis(1,3-dithiol-2-ylidene)-Substituted Subtriazachlorin: A Subphthalocyanine Analogue with Redox Properties

Bis(1,3-dithiol-2-ylidene)-substituted subtriazachlorin was formed because of an unusual reaction of a 1,3-dithiole-2-one-fused subphthalocyanine in a triethylphosphite-mediated tetrathiafulvalene synthesis. In this novel molecule, the bis(1,3-dithiol-2-ylidene)ethane moiety and subtriazachlorin structure are fused, resulting in an electron-donating ability and broad absorption in the near-infrared region.

Boron(III) Carbazosubphthalocyanines: Core-Expanded Antiaromatic Boron(III) Subphthalocyanine Analogues

Condensation of 1,8-diamino-3,6-dichlorocarbazole with a series of disubstituted 1,3-diiminoisoindolines, followed by treatment with BF₃ ⋅OEt₂ led to the formation of the corresponding core-expanded boron(III) subphthalocyanine analogues. These air-stable π-conjugated boron(III) carbazosubphthalocyanines possess two boron-containing seven-membered-ring units and a 16 π-electron skeleton, and represent the first examples of antiaromatic boron(III) subphthalocyanine analogues as supported by spectroscopic and theoretical studies. The molecular structure of one of these compounds was unambiguously determined by single-crystal X-ray diffraction analysis. In contrast to typical boron(III) subphthalocyanines, which adopt a cone-shaped structure, the π skeleton of this compound is almost planar.

Fluorinated boron subphthalocyanines: Lewis acid based templating chemistry facilitates random halide exchange, and fluoride versus chloride affects the basic photophysical properties and the solid-state arrangement

A sub-group of the phthalocyanine family, the boron subphthalocyanines (BsubPcs), have robust chemistry and can be readily modified at the axial and peripheral positions to tune their physical properties.

Low-Symmetry Mixed Fluorinated Subphthalocyanines as Fluorescence Imaging Probes in MDA-MB-231 Breast Tumor Cells

Boron subphthalocyanines (SPcs) are aromatic macrocycles that possess a combination of physical and optical properties that make them excellent candidates for application as fluorescent imaging probes. These molecules have intense electronic absorption and emission, and structural versatility that allows for specific tuning of physical properties. Herein, we report the synthesis of a series of low-symmetry fluorinated SPcs and compare them to analogous compounds with varying numbers of peripheral fluorine atoms and varied aromaticity. Across the series, with increasing addition of fluorine atoms to the periphery of the ring, a downfield chemical shift in ¹⁹F NMR and a bathochromic shift of electronic absorption were observed. Expanding the size of the aromatic ring by replacing peripheral benzo- groups with naphtho- groups prompted a far more drastic bathochromic shift to absorption and emission. Fluorescence quantum yields (Φ_f) proved to be sufficiently high to observe intracellular fluorescence from MDA-MB-231 breast tumor cells in vitro by epifluorescence microscopy; fluorination proved vital for this purpose to improve solubility. This report lays the groundwork for the future development of these promising SPcs for their ultimate application as near-infrared (NIR) fluorescent imaging probes in biological systems.

Integration of inherent and induced chirality into subphthalocyanine analogue

Conventional conjugated systems are characteristic of only either inherent or induced chirality because of synthetic challenge in combination of chiral segment into the main chromophore. In this work, chiral binaphthyl segment is directly fused into the central chromophore of a subphthalocyanine skeleton, resulting in a novel type of chiral subphthalocyanine analogue (R/S)-1 of integrated inherent and induced chirality. Impressively, an obviously enhanced optical activity is discerned for (R/S)-1 molecules, and corresponding enhancement mechanism is elucidated in detail. The synthesis strategy based on rational molecular design will open the door towards fabrication of chiral materials with giant optical activity, which will have great potential in chiroptical devices.

The first porphyrin–subphthalocyaninatoboron(iii)-fused hybrid with unique conformation and intramolecular charge transfer behavior

The first porphyrin–subphthalocyaninatoboron(iii)-fused hybrid with unique conformation and intramolecular charge-transfer behaviour has been isolated and structurally characterized.

Optical absorption of warped nanographenes tuned by five- and seven-membered carbon rings

The introduction of multiple carbon rings is one of the common ways for graphene modification. Starting from warped C80H30 nanographene, which consists of a number of six- and seven-membered carbon rings (C6 and C7) centering at a five-membered carbon ring (C5), we explored the structure and property variations of its derivatives in which their C7 rings were gradually replaced with C6 rings. With reducing number of C7 rings, their curved boundary with the C6 rings becomes flat until a bowl-like structure is formed when all the C7 rings disappear. The optical absorption spectra vary accordingly. Both the α-bands and the maximum absorption bands in the visible region are related to the number and location of the C7 rings. Further analysis of the excited states of the C80H30 derivatives, as well as on the designed model systems, revealed that the C7 rings affect the electron excitations in two ways. In addition to their participation in electronic transitions, they control the composition of molecular orbitals that are involved in the excitations. The highest occupied molecular orbitals are mainly contributed by atoms on the C6 and C7 rings, while the lowest unoccupied molecular orbitals by atoms on the C5 and C6 rings. Our study sheds some light on how the multiple carbon rings affect the optical absorption of nanographenes and provides information for the preparation of nanographenes with tunable structural and optical properties.

Crystal structure of [1,1'-biphen-yl]-2,2'-dicarbo-nitrile

The complete mol­ecule of the title compound, C₁₄H₈N₂, is generated by a twofold rotation axis located at the midpoint of the biphenyl C—C bond. The dihedral angle between the symmetry-related phenyl rings is 46.16 (3)°. In the crystal, mol­ecules are linked by slipped parallel π–π inter­actions [centroid–centroid distance = 3.9451 (7) Å, normal distance = 3.6293 (5) Å, slippage 1.547 Å], forming columns along the b-axis direction.

Cyclophanes containing bowl-shaped aromatic chromophores: three isomers of anti-[2.2](1,4)subphthalocyaninophane

The connection of bowl-shaped aromatic boron subphthalocyanines with anti-[2.2]paracyclophane resulted in the first observation of electronic communication between convex and concave surfaces. Three isomers of anti-[2.2](1,4)subphthalocyaninophane, described as concave-concave (CC), convex-concave (CV), and convex-convex (VV) according to the orientation of the subphthalocyanine units, were synthesized and characterized by various spectroscopic techniques, including (1) H NMR, electronic absorption, fluorescence, and magnetic circular dichroism spectroscopy and X-ray crystallography, together with molecular-orbital calculations. On going from the CC system to CV and further to VV, the Q band broadened and finally split as a result of through-space expansion of the conjugated systems, which were also reproduced theoretically.

Structurally-modified subphthalocyanines: molecular design towards realization of expected properties from the electronic structure and structural features of subphthalocyanine

This feature article summarizes recent contributions of the authors in the synthesis of structurally-modified subphthalocyanines, which covers (1) modification of the conjugated system, (2) core-modification, and (3) exterior-modification.