Peripherally Cyanated Subphthalocyanines as Potential n-Type Organic Semiconductors

Bulking Up the Bay-Position Substituents Enables Enhanced Selectivity of Cs-Symmetric Boron Subphthalocyanine-Subnaphthalocyanine Hybrids

The precise synthesis of subporphyrinoid hybrids with π-expanded topologies and unique material properties plays a promising role in the design of functional macrocycles. Easy, selective, and controllable routes to boron subphthalocyanine-subnaphthalocyanine hybrids, Bsub(Pc3-p-Ncp)s, are desirable for this purpose yet synthetically challenging due to random mixtures of Cs-, C3v-, and, in some cases, C1-symmetric compounds that form during traditional statistical mixed cyclotrimerizations. Herein, we addressed this issue by developing a sterically driven mixed cyclotrimerization with enhanced selectivity for the targeted Cs-symmetric hybrid and complete suppression of sterically crowded macrocyclic byproducts. This process, coupled with a rationally designed precursor bearing bulky phenyl substituents, enabled the synthesis and characterization of bay-position phenylated Ph2-(Rp)8Bsub(Pc2-Nc1) hybrids with halogens (Rp = Cl or F) in their peripheral isoindole rings. Reaction selectivity ranged between 59 and 72% with remarkable yields, significantly higher than that of conventional mixed cyclotrimerizations. These findings were augmented by theoretical calculations on precursor Lewis basicity as guiding principles into hybrid macrocycle formation. Additionally, the incorporation of unfused phenyl groups and halogen atoms into the hybrid framework resulted in fine-tuned optical, structural, electronic, and electrochemical properties. This straightforward approach achieved improved selectivity and controlled narrowing of the product distribution, affording the efficient synthesis of structurally sophisticated Bsub(Pc2-Nc1) hybrids. This then expands the library of 3-dimensional π-extended macrocycles for use in a range of applications, such as in optoelectronic devices with precisely tailored optical properties.

Tetra(peri-naphthylene)anthracene: A Near-IR Fluorophore with Four-Stage Amphoteric Redox Properties

A novel, benign synthetic strategy towards soluble tetra(peri-naphthylene)anthracene (TPNA) decorated with triisopropylsilylethynyl substituents has been established. The compound is perfectly stable under ambient conditions in air and features intense and strongly bathochromically shifted UV/vis absorption and emission bands reaching to near-IR region beyond 900 nm. Cyclic voltammetry measurements revealed four facilitated reversible redox events comprising two oxidations and two reductions. These remarkable experimental findings were corroborated by theoretical studies to identify the TPNA platform a particularly useful candidate for the development of functional near-IR fluorophores upon appropriate functionalization.

Recent advances in subphthalocyanines and related subporphyrinoids

Subporphyrinoids constitute a class of extremely versatile and attractive compounds. Herein, a comprehensive review of the most recent advances in the fundamentals and applications of these cone-shaped aromatic macrocycles is presented.

Subphthalocyanines as Efficient Photosensitizers with Nanomolar Photodynamic Activity against Cancer Cells

Because cancer is the second leading cause of death globally, investigation of new photosensitizers for photodynamic therapy is highly desirable. In this work, different peripherally substituted subphthalocyanines (SubPcs) with either a benzocrown moiety (CE-) or a tyrosine methyl ester (Tyr-) as the axial ligand have been prepared. Target SubPcs showed high Φ_Δ values, >0.50 in EtOH. Both CE- and Tyr- moieties increased substantially the hydrophilicity of the compounds (log P = 1.79-2.63, n-octanol/PBS). Uptake to cells, subcellular localization, and monitoring of the progression of cell death over time are described. Improved spectroscopic behavior of the CE- series in cell culture medium resulted in higher photodynamic activity versus that of the Tyr- series. In particular, the peripherally triethylsulfanyl SubPc-CE exhibited extraordinarily low EC₅₀ values of 2.3 and 4.4 nM after light activation and high TC₅₀ values of 14.49 and 5.25 μM (i.e., dark toxicity without activation) on SK-MEL-28 and HeLa cells, respectively, which rank it among the best photosensitizers ever.

Subphthalocyaninato Boron(III) Hydride: Synthesis, Structure and Reactivity

Subphthalocyanine (SubPc) chemistry has been limited so far by their high sensitivity toward strong nucleophiles. In particular, the substitution of the axial chlorine atom by a nucleophilic group in the case of less-reactive SubPcs, such as those bearing electron-withdrawing peripheral substituents, presents some limitations and requires harsh conditions. By taking advantage of the electrophilic character of DIBAL-H, it has been possible to prepare for the first time SubPc-hydride derivatives that exhibit high reactivity as hydroboration reagents of aldehydes. This hydride transfer requires using a typical carbonyl activator (trimethylsilyl triflate) and only one equivalent of aldehyde, affording SubPcs with an axial benzyloxy group in good yield. This transformation has proven to be a useful alternative method for the axial functionalisation of dodecafluoroSubPc, a paradigmatic SubPc derivative, by using electrophiles for the first time. Considering the increasing interest in SubPcs as electron-acceptor semiconductors with remarkable absorption in the visible range to replace fullerene in organic photovoltaic (OPV) devices, it is of the utmost importance to develop new synthetic methodologies for their axial functionalisation.

Panchromatic Light Harvesting and Stabilizing Charge-Separated States in Corrole-Phthalocyanine Conjugates through Coordinating a Subphthalocyanine

Owing to the electron-donating and -accepting nature of corroles (Corr) and phthalocyanines (Pc), respectively, we designed and developed two novel covalently linked Corr-Pc conjugates. The synthetic route allows the preparation of the target conjugates in satisfying yields. Comprehensive steady-state absorption, fluorescence, and electrochemical assays enabled insights into energy and electron-transfer processes upon photoexcitation. Coordinating a pyridine-appended subphthalocyanine (SubPc) to the Pc of the conjugate sets up the ways and means to realize the first example of an array composed by three different porphyrinoids, which drives a cascade of energy and charge-transfer processes. Importantly, the SubPc assists in stabilizing the charge-separated state, that is, one-electron oxidized Corr and the one electron-reduced Pc, upon photoexcitation by means of a reductive charge transfer to the SubPc. To the best of our knowledge, this is the first case of an intramolecular oxidation of a Corr within electron-donor-acceptor conjugates by means of just photoexcitation. Moreover, the combination of Corr, Pc, and SubPc guarantees panchromatic absorption across the visible range of the solar spectrum, with the SubPc covering the "green gap" that usually affects porphyrinoids.