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.

Photochemical α-Aminonitrile Synthesis Using Zn-Phthalocyanines as Near-Infrared Photocatalysts

While photochemical transformations with sunlight almost exclusively utilize the UV-vis part of the solar spectrum, the majority of the photons emitted by the sun have frequencies in the near-infrared region. Phthalocyanines show high structural similarity to the naturally occurring light-harvesting porphyrins, chlorins, and mainly bacteriochlorins and are also known for being efficient and affordable near-infrared light absorbers as well as triplet sensitizers for the production of singlet oxygen. Although having been neglected for a long time in synthetic organic chemistry due to their low solubility and high tendency toward aggregation, their unique photophysical properties and chemical robustness make phthalocyanines attractive photocatalysts for the application in near-infrared-light-driven synthesis strategies. Herein, we report a cheap, simple, and efficient photocatalytic protocol, which is easily scalable under continuous-flow conditions. Various phthalocyanines were studied as near-infrared photosensitizers in oxidative cyanations of tertiary amines to generate α-aminonitriles, a synthetically versatile compound class.

Fluorinated Zinc and Copper Phthalocyanines as Efficient Third Components in Ternary Bulk Heterojunction Solar Cells

Fluorinated zinc and copper metallophthalocyanines MPcF48 are synthesized and incorporated as third component small molecules in ternary organic solar cells (TOSCs). To enable the high performance of TOSCs, maximizing short-circuit current density (J SC) is crucial. Ternary bulk heterojunction blends, consisting of a polymer donor PTB7-Th, fullerene acceptors PC70BM, and a third component MPcF48, are formulated to fabricate TOSCs with a device architecture of ITO/PFN/active layer/V2O5/Ag. Employing copper as metal atom substitution in the third component of TOSCs enhances J SC as a result of complementary absorption spectra in the near-infrared region. In combination with J SC enhancement, suppressed charge recombination, improved exciton dissociation and charge carrier collection efficiency, and better morphology lead to a slightly improved fill factor (FF), resulting in a 7% enhancement of PCE than those of binary OSCs. In addition to the increased PCE, the photostability of TOSCs has also been improved by the appropriate addition of CuPcF48. Detailed studies imply that metal atom substitution in phthalocyanines is an effective way to improve J SC, FF, and thus the performance and photostability of TOSCs.

Synthesis of a Naphthalocyanine-Like Dye: The First Report on Zn(II)-1,6-methano[10]annulenecyanine

The synthesis of the new dye 1,6-methano[10]annulenecyanine is described. For this purpose, the 3,4-dicyano-1,6-methano[10]annulene and 3,4-carboxyimide-1,6-methano[10]annulene buildings blocks were synthesized in six to eight steps. In both cases, these building blocks were then cyclotetramerized to furnish a new Zn(II)-1,6-methano[10]annulenecyanine which presents a strong red-shifted absorption band at 800 nm and high solubility in common organic solvents.

Porphyrin–diketopyrrolopyrrole conjugates and related structures: Synthesis, properties and applications

A large diversity of porphyrin–diketopyrrolopyrrole conjugates and related structures formed by diketopyrrolopyrrole units and pyrrole-based moieties such as phthalocyanine, porphycene, calix[4]pyrrole or BODIPY have been reported since 2010. The new compounds, whether small molecules or polymeric materials, exhibit very interesting photophysical properties and have been tested in a range of technical or biological applications. This review summarizes the advances in the synthesis of such compounds. Their photophysical properties and potential applications are also briefly discussed.

BODIPY substituted zinc(II) phthalocyanine and its bulk heterojunction application in solar cells

A novel asymmetrical zinc(II) phthalocyanine-BODIPY conjugate (ZnPc-BODIPY) bearing three iodine groups directly substituted to the macrocycle and one BODIPY connected to the macrocycle with an amide bond was synthesized by the reaction of carboxylic-acid-substituted asymmetrical zinc(II) phthalocyanine (ZnPc) with the BODIPY-derivative-bearing amino group (BODIPY-NH2). This conjugate was fully characterized by spectroscopic methods (FT-IR, UV-vis, 1H NMR, 11B NMR, 19F NMR and mass) and elemental analysis. The fluorescence behavior of ZnPc-BODIPY was studied to determine the energy transfer process. Voltammetry measurements (CV and SWV) were performed to specify the HOMO–LUMO energy levels and band gaps of ZnPc-BODIPY and starting compounds (ZnPc and BODIPY-NH2) for comparison. In addition, the band gaps of these compounds were also determined by UV-vis absorption onset (λonset) and theoretical calculations. Bulk heterojunction solar cells containing ZnPc-BODIPY were fabricated in the structure of ITO/PEDOT:PSS/ZnPc-BODIPY:PCBM/Al. The photovoltaic parameters of the solar cell were obtained and the ZnPc-BODIPY conjugate was found to bring spectral contribution to IPCE at a peak of 510 nm.

p-Phenylene-bridged zinc phthalocyanine-dimer as hole-transporting material in perovskite solar cells

The synthesis and characterization of a [Formula: see text]-phenylene-bridged ZnPc dimer along with a preliminary study of this material as hole transporting material (HTM) in perovskite solar cells is described. The maximum efficiencies that obtained are 15.2% for ZnPc-[Formula: see text]-ZnPc 1, thus demonstrating the potential of the Pc dimers that could pave the path to achieve highly efficient PSCs (PCE >20%).

Design of Diketopyrrolopyrrole (DPP)-Based Small Molecules for Organic-Solar-Cell Applications

After the first report in 2008, diketopyrrolopyrrole (DPP)-based small-molecule photovoltaic materials have been intensively explored. The power conversion efficiencies (PCEs) for the DPP-based small-molecule donors have been improved up to 8%. Furthermore, through judicious structure modification, DPP-based small molecules can also be converted into electron-acceptor materials, and, recently, some exciting progress has been achieved. The development of DPP-based photovoltaic small molecules is summarized here, and the photovoltaic performance is discussed in relation to structural modifications, such as the variations of donor-acceptor building blocks, alkyl substitutions, and the type of conjugated bridges, as well as end-capped groups. It is expected that the discussion will provide a guideline in the exploration of novel and promising DPP-containing photovoltaic small molecules.