A Greener Route to Blue: Solid-State Synthesis of Phthalocyanines

Phthalocyanines are important organic dyes with a broad applicability in optoelectronics, catalysis, sensing and nanomedicine. Currently, phthalocyanines are synthetized in high boiling organic solvents, like dimethylaminoethanol (DMAE), which is a flammable, corrosive, and bioactive substance, miscible with water and harmful to the environment. Here we show a new solid-state approach for the high-yielding synthesis of phthalocyanines, which reduces up to 100-fold the amount of DMAE. Through systematic screening of solid-state reaction parameters, carried out by ball-milling and aging, we reveal the influence of key variables-temperature, presence of a template, and the amount and role of DMAE in the conversion of tBu phthalonitrile to tetra-tBu phthalocyanine. These results set the foundations to synthesize these high-performance dyes through a greener approach, opening the field of solid-state synthesis to a wider family of phthalocyanines.

Phthalocyanine and Its Formulations: A Promising Photosensitizer for Cervical Cancer Phototherapy

Cervical cancer is one of the most common causes of cancer-related deaths in women worldwide. Despite advances in current therapies, women with advanced or recurrent disease present poor prognosis. Photodynamic therapy (PDT) has emerged as an effective therapeutic alternative to treat oncological diseases such as cervical cancer. Phthalocyanines (Pcs) are considered good photosensitizers (PS) for PDT, although most of them present high levels of aggregation and are lipophilic. Despite many investigations and encouraging results, Pcs have not been approved as PS for PDT of invasive cervical cancer yet. This review presents an overview on the pathophysiology of cervical cancer and summarizes the most recent developments on the physicochemical properties of Pcs and biological results obtained both in vitro in tumor-bearing mice and in clinical tests reported in the last five years. Current evidence indicates that Pcs have potential as pharmaceutical agents for anti-cervical cancer therapy. The authors firmly believe that Pc-based formulations could emerge as a privileged scaffold for the establishment of lead compounds for PDT against different types of cervical cancer.

Facile, Mild-Temperature Synthesis of Metal-Free Phthalocyanines

It is important for the synthesis and research of phthalocyanine compounds for these compounds to be easily obtained at low temperature. We observed that metal-free phthalocyanine was sometimes found in a simple system used to synthesize phthalocyanine precursors at room temperature, and further studies showed that the key to the effective formation of phthalocyanines at low temperature lay in the presence of equal volumes of alcohol and amine, in addition to substrate phthalonitriles and solvents, in the reaction system. A synthetic mechanism was proposed and facile syntheses have been realized, such as the synthesis of tetra-α(β)-nitrophthalocyanines and tetra-α(β)-(4-tert-butylphenoxy)phthalocyanines from the corresponding substituted phthalonitriles at mild temperature (37 °C). The results are significant for the design and synthesis of new phthalocyanine derivatives, and the method is convenient and easy to adopt for general use in standard laboratories.

Sustainable Approaches to the Synthesis of Metallophthalocyanines in Solution

This work aims to investigate more sustainable reaction conditions for the synthesis of metallophthalocyanines. Anisole, glycerol and their mixtures have been investigated as reaction media for the tetramerization of phthalonitriles. Acetates of three divalent first-transition metal cations, Co(II), Cu(II) and Zn(II), were used and several bases were tested, depending on the chosen substrates and reaction conditions, with a view to making the whole process more sustainable while ensuring its scalability. Unsubstituted phthalocyanines were synthesized to analyze the behavior of the different metal ions in terms of reactivity in the new reaction media, resulting in a general Cu > Co > Zn trend, while the nonpolar tetra-tert-butyl substitution was investigated to evaluate the synthesis of soluble derivatives in the new conditions. Furthermore, the potassium hydroxide (KOH)-aided statistical synthesis of the unsymmetrical 9(10), 16(17), 23(24)-tri-tert-butyl-2-iodophthalocyaninato zinc(II), starting from 4-tert-butylphthalonitrile and 4-iodophthalonitrile in a glycerol/anisole mixture, proceeded with a satisfactory 26% yield. Our results provide insights into the investigation of new reaction environments and the understanding of their strengths and weaknesses, with a view to further increasing the sustainability of the synthesis of metallomacrocycles with high added value while lowering their production cost.

Preparation and Characterization of Cu and Ni on Alumina Supports and Their Use in the Synthesis of Low-Temperature Metal-Phthalocyanine Using a Parallel-Plate Reactor

Ni- and Cu/alumina powders were prepared and characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), and N₂ physisorption isotherms were also determined. The Ni/Al₂O₃ sample reveled agglomerated (1 μm) of nanoparticles of Ni (30-80 nm) however, NiO particles were also identified, probably for the low temperature during the H₂ reduction treatment (350 °C), the Cu/Al₂O₃ sample presented agglomerates (1-1.5 μm) of nanoparticles (70-150 nm), but only of pure copper. Both surface morphologies were different, but resulted in mesoporous material, with a higher specificity for the Ni sample. The surfaces were used in a new proposal for producing copper and nickel phthalocyanines using a parallel-plate reactor. Phthalonitrile was used and metallic particles were deposited on alumina in ethanol solution with CH₃ONa at low temperatures; ≤60 °C. The mass-transfer was evaluated in reaction testing with a recent three-resistance model. The kinetics were studied with a Langmuir-Hinshelwood model. The activation energy and Thiele modulus revealed a slow surface reaction. The nickel sample was the most active, influenced by the NiO morphology and phthalonitrile adsorption.

Improved syntheses of high hole mobility phthalocyanines: A case of steric assistance in the cyclo-oligomerisation of phthalonitriles

It has been shown that the base-initiated cyclo-oligomerisation of phthalonitriles is favoured by bulky α-substituents making it possible to obtain the metal-free phthalocyanine directly and in high yield. The phthalocyanine with eight α-isoheptyl substituents gives a high time-of-flight hole mobility of 0.14 cm²·V⁻¹·s⁻¹ within the temperature range of the columnar hexagonal phase, that is 169–189 °C.