18π-Electron Tautomeric Benziphthalocyanine: A Functional Near-Infrared Dye with Tunable Aromaticity

20π-Electron Antiaromatic Benziphthalocyanines with Absorption Reaching the Near-Infrared-II Region

Although second near-infrared (NIR-II, 1000-1500 nm) light has attracted considerable attention, especially for life sciences applications, the development of organic dyes with NIR-II absorption remains a formidable challenge. Herein we report the design, synthesis, and electronic properties of 20π-electron antiaromatic benziphthalocyanines (BPcs) that exhibit intense absorption bands in the NIR region. The strong, low-energy absorption of the antiaromatic BPcs is attributed to electric-dipole-allowed HOMO-LUMO transitions with narrow band gaps, enabled by the reduced structural symmetry of BPc compared with regular porphyrins and phthalocyanines. The combination of peripheral substituents and a central metal decreases the HOMO-LUMO energy gaps, leading to the extension of the absorption bands into the NIR-II region (reaching 1100 nm) under reductive conditions.

Organic Electrode Materials for Dual-Ion Batteries

Organic materials are widely used in various energy storage devices due to their renewable, environmental friendliness and adjustable structure. Dual-ion batteries (DIBs), which use organic materials as the electrodes, are an attractive alternative to conventional lithium-ion batteries for sustainable energy storage devices owing to the advantages of low cost, environmental friendliness, and high operating voltage. To date, various organic electrode materials have been applied in DIBs. In this review, we present the development of DIBs with a following brief introduction of characteristics and mechanisms of organic materials. The latest progress in the application of organic materials as anode and cathode materials for DIBs is mainly reviewed. Finally, we also discussed the challenges and prospects of organic electrode materials for DIBs.

Synthesis and Characterization of Bulky Substituted Hemihexaphyrazines Bearing 2,6-Diisopropylphenoxy Groups

New substituted [30]trithiadodecaazahexaphyrines (hemihexaphyrazines) were synthesized by a crossover condensation of 2,5-diamino-1,3,4-thiadiazole with 4-chloro-5-(2,6-diisopropylphenoxy)- or 4,5-bis-(2,6-diisopropylphenoxy)phthalonitriles. The compounds were characterized by 1H-, 13C-NMR, including COSY, HMBC, and HSQC spectroscopy, MALDI TOF spectrometry, elemental analysis, IR and UV-Vis absorbance and fluorescence techniques.

A Switchable Near-Infrared-Absorbing Dye Based on Redox-Bistable Benzitetraazaporphyrin

Activatable near-infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench-stable 18π- and 20π-electron benzitetraazaporphyrins (BzTAPs) possessing redox-switchable NIR properties. X-Ray, NMR, and UV/Visible-NIR analyses revealed that 20π-electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring-current, while 18π-electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR-silent BzTAP 2 was readily converted to the NIR-active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry-lowering perturbation of the 20π-electron porphyrinoid skeleton enables the HOMO-LUMO transition of 1 to be electric-dipole-allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments.

Low-Symmetry Phthalocyanines Bearing Carboxy-Groups: Synthesis, Spectroscopic and Quantum-Chemical Characterization

The synthesis and characterization of A₃B-type phthalocyanines, ZnPc1–4, bearing bulky 2,6-diisopropylphenoxy-groups or chlorine atoms on isoindoline units “A” and either one or two carboxylic anchors on isoindoline unit “B” are reported. A comparison of molecular modelling with the conventional time dependent—density functional theory (TD-DFT) approach and its simplified sTD-DFT approximation provides further evidence that the latter method accurately reproduces the key trends in the spectral properties, providing colossal savings in computer time for quite large molecules. This demonstrates that it is a valuable tool for guiding the rational design of new phthalocyanines for practical applications.

Temperature-dependent changes in the molecular orientation and visible color of phthalocyanine films

A simple phthalocyanine zinc complex exhibits a visible color change in response to weak external stimuli, i.e., changes in solvent and temperature. Its chromism was attributed to its controlled aggregation via weak interactions between the central metal and peripheral oxygen atoms. In solution, intense absorption and fluorescence bands appeared in both the longer-wavelength and NIR region in non-coordinating solvents, while a simple sharp Q band was observed in coordinating solvents. Variable-temperature absorption spectra and fluorescence lifetime measurements were used to characterize the aggregation-induced absorption and emission in non-coordinating solvents. A selective aggregation–disaggregation process was also observed in thin films of this phthalocyanine zinc complex, and the optical properties of the film depend on the annealing temperature. The changes in the NIR region lead to a sizable visible color change that is recognizable by the naked human eye. The temperature-dependent control of the aggregation process in the thin film was confirmed using operando spectroscopy techniques.

A simple phthalocyanine zinc complex exhibits a visible color change in response to weak external stimuli, i.e., changes in solvent and temperature.

Antiaromatic or Nonaromatic? 21 H,61 H-2,6(2,5)-Dipyrrola-1,5(2,6)-dipyridinacyclooctaphane-3,7-diene: a Porphycene Derivative with 4 N π Electrons

A porphycene-derived compound with a 20 π-electron skeleton has been obtained by replacing two pyrrolene units of porphycene by pyridine rings. NMR, electronic absorption and MCD spectra, and the lack of fluorescence are typical for 4 N cyclic π electron systems. The electronic structure and the differences with respect to porphycene can be rationalized by treating these compounds as perturbed, doubly positively charged [22]annulene and [20]annulene perimeters, respectively. Even though the spectroscopic and photophysical criteria proposed for antiaromatic systems are fulfilled, the molecule is very stable. We argue that the compound should be characterized as nonaromatic rather than antiaromatic. The perimeter model is recommended as a powerful tool for predicting the electronic structure and spectra and as a useful addition to other methods that probe the aromaticity.

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.

Changes of phthalocyanine visible color caused by near-IR solvatochromism

Herein, we show that the Zn complex of 1,4,8,11,15,18,22,28-octakis(butoxy)phthalocyanine exhibits solvatochromism and characterize the corresponding visible color changes. In particular, we reveal that although the variation of the solvent-dependent position of the Q band is relatively small (~100 nm), the solution colors change from red to yellow and green depending on the composition of the solvent mixture. Moreover, the above Q band was located at the border between the visible and near-IR regions, [Formula: see text]. its red shift could not be directly recognized by the human naked eye. Substituents on oxygen atoms were shown to influence phthalocyanine aggregation and thus affect near-IR absorption, with the observed near-IR solvatochromism providing a new strategy of color change in response to weak external stimuli.

A hindered subphthalocyanine that forms crystals with included aromatic solvent but will not play ball with C60

A novel subphthalocyanine containing bulky substituents placed at its peripheral sites (i.e. 2,3,9,10,16,17-hexa(2′,6′-di-iso-propylphenoxy)boron subphthalocyanine) was prepared and assessed for supramolecular binding with C[Formula: see text], through crystallisation and fluorescence studies. Three different crystal polymorphs of the subphthalocyanine were obtained that showed inclusion of a single aromatic solvent molecule within the well-defined cavity of the molecule but complete exclusion of C[Formula: see text]. Analysis of the crystal structures indicated that the bowl-shaped cavity of the subphthalocyanine molecule was only accessible to small molecules due to the steric congestion surrounding the macrocycle, which results in hindered rotation of the substituents on the NMR timescale. Enhanced solubility, up to 42.0 g/L in common organic solvents, was demonstrated consistent with the crystal structures which are dominated by relatively weak intermolecular interactions, which allow solvent molecules to play a role in crystallisation.

Benziporphyrins, a unique platform for exploring the aromatic characteristics of porphyrinoid systems

Benziporphyrins and related systems exhibit a wide range of properties and may possess nonaromatic, strongly aromatic or even antiaromatic characteristics.

Synthesis and properties of palladium(II) complexes of aromatic hemiporphyrazines

Palladium(II) complexes of aromatic hemiporphyrazines were prepared by the reaction of bis(dibenzylideneacetone)palladium(0) with the corresponding metal-free macrocycles. Single crystal X-ray analysis revealed that a palladium(II) ion was coordinated inside the macrocyclic cavity to form two Pd – C bonds. Electronic properties of the metalloorganic compounds were characterized by NMR, UV-vis-NIR, and magnetic circular dichroism (MCD) spectroscopy.

Relative stability of benziporphyrin and naphthiporphyrin tautomers and the emergence of macrocyclic diatropicity

The conformations and relative stabilities of a series of benziporphyrin and naphthiporphyrin tautomers were calculated and the diatropic properties of each of these species were assessed. The results were in good agreement with experimental observations and allow favorable delocalization pathways to be identified.