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

Phthalocyanines Synthesis: A State-of-The-Art Review of Sustainable Approaches Through Green Chemistry Metrics

Driven by escalating environmental concerns, synthetic chemistry faces an urgent need for a green revolution. Green chemistry, with its focus on low environmental impacting chemicals and minimized waste production, emerges as a powerful tool in addressing this challenge. Metrics such as the E-factor guide the design of environmentally friendly strategies for chemical processes by quantifying the waste generated in obtaining target products, thus enabling interventions to minimize it. Phthalocyanines (Pcs), versatile molecules with exceptional physical and chemical properties, hold immense potential for technological applications. This review aims to bridge the gap between green chemistry and phthalocyanine synthesis by collecting the main examples of environmentally sustainable syntheses documented in the literature. The calculation of the E-factor of a selection of them provides insights on how crucial it is to evaluate a synthetic process in its entirety. This approach allows for a better evaluation of the actual sustainability of the phthalocyanine synthetic process and indicates possible strategies to improve it.

Contracted porphyrins and calixpyrroles: synthetic challenges and ring-contraction effects

Ring-contracted porphyrin analogues, such as subporphyrins and calix[3]pyrroles, have recently attracted considerable attention not only as challenging synthetic targets but also as functional macrocyclic compounds. Although canonical porphyrins and calix[4]pyrrole are selectively generated via acid-catalyzed condensation reactions of pyrrole monomers, their tripyrrolic analogues are always missing under similar conditions. Recent progress in synthesis has shown that strain-controlled approaches using boron(iii)-templating, core-modification, or ring tightening provide access to various contracted porphyrins. The tripyrrolic macrocycles are a new class of functional macrocycles exhibiting unique ring-contraction effects, including strong boron chelation and strain-induced ring expansion. This Perspective reviews recent advances in synthetic strategies and the novel ring-contraction effects of subporphyrins, triphyrins(2.1.1), calix[3]pyrroles, and their analogous.

Pressure-Induced Amidine Formation via Side-Chain Polymerization in a Charge-Transfer Cocrystal

Compression of small molecules can induce solid-state reactions that are difficult or impossible under conventional, solution-phase conditions. Of particular interest is the topochemical-like reaction of arenes to produce polymeric nanomaterials. However, high reaction onset pressures and poor selectivity remain significant challenges. Herein, the incorporation of electron-withdrawing and -donating groups into π-stacked arenes is proposed as a strategy to reduce reaction barriers to cycloaddition and onset pressures. Nevertheless, competing side-chain reactions between functional groups represent alternative viable pathways. For the case of a diaminobenzene:tetracyanobenzene cocrystal, amidine formation between amine and cyano groups occurs prior to cycloaddition with an onset pressure near 9 GPa, as determined using vibrational spectroscopy, X-ray diffraction, and first-principles calculations. This work demonstrates that reduced-barrier cycloaddition reactions are theoretically possible via strategic functionalization; however, the incorporation of pendant groups may enable alternative reaction pathways. Controlled reactions between pendant groups represent an additional strategy for producing unique polymeric nanomaterials.

Innovative Design Strategies Advance Biomedical Applications of Phthalocyanines

Owing to their long absorption wavelengths, high molar absorptivity, and tunable photosensitivity, phthalocyanines have been widely used in photodynamic therapy (PDT). However, phthalocyanines still face the drawbacks of poor targeting, "always-on" photosensitizing properties, and unsatisfactory therapeutic efficiency, which limit their wide applications in biomedical fields. Thus, new design strategies such as modification of targeting molecules, formation of nanoparticles, and activating photosensitizers are developed to improve the above defects. Notably, recent studies have shown that novel phthalocyanines are not only used in fluorescence imaging and PDT, but also in photoacoustic imaging, photothermal imaging, sonodynamic therapy, and photothermal therapy. This review focuses on recent design strategies, applications in biomedicine, and clinical development of phthalocyanines, providing ideas and references for the design and application of phthalocyanine, so as to promote their future transformation into clinical applications.