Efficient Synthesis of ABAB Functionalized Phthalocyanines

Recent Developments in Isoindole Chemistry

Isoindoles are highly reactive aromatic heterocycles that have a variety of important applications in areas such as medicine, analytical detection, and solar energy. Due to their highly reactive nature, isoindoles can be used to access their derivatives, which possess a diverse array of biological activities. However, their reactivity also makes isoindoles unstable and thus, difficult to prepare. Consequently, there has been a need for the development of novel methods that address some of the synthetic challenges and limitations, as well as reactions that utilize isoindoles to access potentially useful compounds. This review will give an overview of the novel reactions reported within the past decade (2012 to 2022) that involve 2H- and 1H-isoindoles and fused isoindoles as reactants, key intermediates, or products. This review is divided into two parts, with the first part focusing on the synthesis of isoindoles and the second part focusing on reactions of isoindoles. The scopes and limitations of the methods described therein will be discussed and the significance of their contributions to the literature will be highlighted. Similar reactions will also be compared.

1 Introduction

2 Synthesis of Isoindoles

2.1 Synthesis of 2H-Isoindoles

2.2 Synthesis of 1H-Isoindoles

3 Reactions of Isoindoles

3.1 Reactions of 2H-Isoindoles

3.2 Reactions of 1H-Isoindoles

4 Conclusions

[3 + 1] Mixed Cyclization: A Synthetic Route to Prepare Low-Symmetry Phthalocyanines

A novel synthetic strategy for low-symmetry phthalocyanines has been developed, which involves the base-promoted cyclization of a preconnected trisphthalonitrile and a free phthalonitrile in the presence of a metal template. By using this [3 + 1] mixed cyclization approach, a series of zinc(II) phthalocyanine derivatives have been synthesized in up to 12% yields, including a very rare ABCD-type phthalocyanine and an amphiphilic ABAC-type analogue that can self-assemble in aqueous media, forming stable spherical nanoparticles.

β-Cyclodextrin-conjugated phthalocyanines as water-soluble and recyclable sensitisers for photocatalytic applications

Two zinc(ii) phthalocyanines substituted with two and four permethylated β-cyclodextrin moieties at the α positions have been synthesised and immobilised on the surface of adamantane-modified silica nanoparticles through host-guest interactions. These molecular and supramolecular systems can catalyse the photooxygenation of 1-naphthol and 2-furoic acid in organic and aqueous media with high conversion efficiency and reaction yield, and photodegradation of 2-chlorophenol in water. Having a higher photostability and recyclability, the supramolecular nanosystems are particularly promising for these photocatalytic applications.

Stacking Control by Molecular Symmetry of Sterically Protected Phthalocyanines

The synthesis and characterization of two phthalocyanine (Pc) structural isomers, 1 and 2, in which four 2,6-di(hexyloxy)phenyl units were attached directly to the 1,8,15,22- or 1,4,15,18-positions of the Pc rings, are described. Both Pcs 1 and 2 exhibited low melting points, i.e., 120 and 130 °C respectively, due to the reduction in intermolecular π-π interaction among the Pc rings caused by the steric hindrance of 2,6-dihexyloxybenzene units. The thermal behaviors were investigated with temperature-controlled polarizing optical microscopy, differential scanning calorimetry, powder X-ray diffraction, and absorption spectral analyses. Pc 1, having C_4h molecular symmetry, organized into a lamellar structure containing lateral assemblies of Pc rings. In contrast, the other Pc 2 revealed the formation of metastable crystalline phases, including disordered stacks of Pcs due to rapid cooling from a melted liquid.

Iridium-catalysed 3,5-bis-borylation of phthalonitrile enables access to a family of C4h octaarylphthalocyanines

Ir-catalysed borylation of phthalonitrile produces both 4-(Bpin)phthalonitrile (1) and 3,5-bis(Bpin)phthalonitrile (2), which are potential divergent intermediates for the synthesis of functionalized phthalocyanines. To exemplify the utility of 2, we have prepared a series of 3,5-bis-arylphthalonitriles that in turn undergo sterically controlled regioselective cyclotetramization to give previously unknown C4h 1,3,8,10,15,17,22,24-octaarylphthalocyanines.

Selective guest recognition by a metallo-organic phthalocyanine-based host

In this manuscript, we have studied the selectivity in the complexation of fullerene species by a Fe[Formula: see text]Pc[Formula: see text] metallo-organic helicate (1) assembled using a bidentate phthalocyanine (Pc) as ligand. The large aromatic internal surface of this helicate shows a strong selectivity towards the encapsulation of C[Formula: see text] from a mixture of C[Formula: see text] and C[Formula: see text]. On the other hand, a bisimidazole-containing naphthalenediimide was used to perform guest exchange experiments over [fullerene [Formula: see text] 1] complexes, taking advantage of the strong coordination bond of the imidazole ring to the Zn centers in the Pc cavity.

Assessing Amphiphilic ABAB Zn(II) Phthalocyanines with Enhanced Photosensitization Abilities in In Vitro Photodynamic Therapy Studies Against Cancer

We have previously demonstrated that singlet oxygen photosensitization abilities of Zn(II) phthalocyanines (Zn(II)Pcs) are enhanced through α-functionalization with bulky fluorinated substituents (i.e., bis(trifluoromethyl)phenyl units) at facing positions of ABAB Zn(II)Pcs, where A and B refer to differently functionalized isoindoles. In this work, we have prepared the Zn(II)Pc ABAB 1 endowed with hydrophilic triethylene glycol monomethyl ether (i.e., at the A isoindoles) to provide solubility in aqueous media, together with its A₃B and A₄ counterparts, and compared their ability to behave as photosensitizers for photodynamic therapy. All photophysical data, aggregation studies and preliminary in vitro biological assays in cell cultures of SCC-13 (squamous cell carcinoma) and HeLa (cervical cancer cells), have proved ABAB 1 as the best photosensitizer of the series.

Fluorine-substituted tetracationic ABAB-phthalocyanines for efficient photodynamic inactivation of Gram-positive and Gram-negative bacteria

Herein, we report the synthesis and characterization of new amphiphilic phthalocyanines (Pcs), the study of their singlet oxygen generation capabilities, and biological assays to determine their potential as photosensitizers for photodynamic inactivation of bacteria. In particular, Pcs with an ABAB geometry (where A and B refer to differently substituted isoindole constituents) have been synthesized. These molecules are endowed with bulky bis(trifluoromethylphenyl) groups in two facing isoindoles, which hinder aggregation and favour singlet oxygen generation, and pyridinium or alkylammonium moieties in the other two isoindoles. In particular, two water-soluble Pc derivatives (PS-1 and PS-2) have proved to be efficient in the photoinactivation of S. aureus and E. coli, selected as models of Gram-positive and Gram-negative bacteria.

Boosting the singlet oxygen photosensitization abilities of Zn(ii) phthalocyanines through functionalization with bulky fluorinated substituents

Non-aggregated, crosswise ZnPcs functionalized with bis(trifluoromethyl)phenyl groups in facing isoindoles have proved efficient photosensitizers for singlet oxygen generation.

Synergy of light harvesting and energy transfer as well as short-range charge shift reactions in multicomponent conjugates

We report herein on the design, the synthesis, and the characterization of a panchromatic, charge stabilizing electron donor-acceptor conjugate: (BBPA)₃-ZnPor-ZnPc-SubPc 1. Each component, that is, bis(biphenyl)phenylamine (BBPA), Zn(ii) porphyrin (ZnPor), Zn(ii) phthalocyanine ZnPc, and subphthalocyanine (SubPc), has been carefully chosen and modified to enable a cascade of energy and charge transfer processes. On one hand, ZnPor, has been functionalized with three electron-donating BBPA as primary and secondary electron donors and to stabilize the final charge-separated state, and, on the other hand, a perfluorinated SubPc has been selected as ultimate electron acceptor. In addition, the ZnPc unit contains several trifluoromethylphenyl moieties to match its energy levels to those of the other components. In fact, irradiation of the heteroarray 1 triggers a cascade of light harvesting across the entire visible range, unidirectional energy transfer, exergonic charge separating, and short-range charge shifting to afford in 14% quantum yield a (BBPA)₃˙⁺-ZnPor-ZnPc-SubPc˙^- charge-separated state. The lifetime of the latter reaches well into the range of tens of nanoseconds.

A giant M2L3 metallo-organic helicate based on phthalocyanines as a host for electroactive molecules

An unprecedented Fe₂Pc₃ metallo-organic helicate has been assembled using a bidentate phthalocyanine (Pc) ligand, 2-formylpyridine and Fe(OTf)₂. This giant helicate has proved itself as a host for large redox-active guests such as fullerene and naphthalenediimide derivatives. Photoactivated electronic interactions between components occur in the host-guest complex.

ABAB Phthalocyanines: Scaffolds for Building Unprecedented Donor-π-Acceptor Chromophores

Unique donor–π–acceptor phthalocyanines have been synthesized through the asymmetric functionalization of an ABAB phthalocyanine, crosswise functionalized with two iodine atoms through Pd‐catalyzed cross‐coupling reactions with adequate electron‐donor and electron‐acceptor moieties. These push–pull molecules have been optically and electrochemically characterized, and their ability to perform as chromophores for dye‐sensitized solar cells has been tested.

Synthesis of an ABCD-Type Phthalocyanine by Intramolecular Cyclization Reaction

Unsymmetrical phthalocyanines with a low symmetry can exhibit unique and intriguing properties that can facilitate their applications in certain disciplines. The synthesis of these compounds, however, has posed a great difficulty. A novel and unprecedented approach for phthalocyanine synthesis is reported that involves intramolecular cyclization of prelinked tetrakisphthalonitriles. By using this strategy, the first ABCD-type phthalocyanine has been prepared in 7.2% yield.

ABAB-type phthalocyanines simultaneously bearing electron donating and electron accepting groups. Synthesis, spectroscopy, and structure

Mg(trans-TPTCPc) was successfully prepared and structurally characterized, representing the first structurally characterized ABAB-type phthalocyanine compound simultaneously bearing electron-donating and electron-accepting groups.