Cyclopentadienylruthenium π Complexes of Subphthalocyanines: A “Drop-Pin” Approach To Modifying the Electronic Features of Aromatic Macrocycles

Tuning Fluorescence and Singlet Oxygen Quantum Yields of Subporphyrazines by Axial Functionalization

The axial functionalization of Subporphyrazines (SubPzs) with unreported alkoxy groups, carboxy and carboperoxy rests, as well as sulfanyl, aryl and amino groups, forming B-O, B-S, B-C, and B-N bonds, respectively, has been investigated. The studied oxygen nucleophiles include aromatic and sterically demanding aliphatic alcohols, along with carboxylic acids and peracids. In general, direct substitution of the chloro-SubPz by oxygen nucleophiles of diverse nature proceeds smoothly, with yields of the isolated alkoxy and carboxy-substituted SubPzs ranging from 49 to 100 %. Conversely, direct substitution with sulphur, carbon and nitrogen nucleophiles do not afford the corresponding substituted SubPzs. In these cases, a stepwise procedure involving an axial triflate-SubPz intermediate was employed, affording only the phenyl-SubPz in 8 % yield. The major compound under these conditions was the unreported SubPz μ-oxo dimer, presumably arising from substitution of the triflate-SubPz by the in situ generated hydroxy-SubPz. This result indicates a quite low reactivity of the TfO-SubPz intermediate with carbon, sulphur and nitrogen nucleophiles. All SubPzs prepared in this work exhibited fluorescence at 510-515 nm with quantum yields ranging from 0.1 to 0.24. Additionally, all SubPzs generated singlet oxygen, with ΦΔ values ranging from 0.15 to 0.57, which show no apparent correlation with the axial substituents.

A Green-to-Near-Infrared Photoswitch Based on a Blended Subporphyrazine-Dithienylethene System

A subporphyrazine (SubPz)-dithienylethene (DTE) photochromic device with 1o and 1c states, was developed and characterized. In this device, the DTE unit can reversibly switch the SubPz absorbance from green to near-infrared [λmax (o/c) = 527 nm/740 nm], as well as the SubPz fluorescence and singlet oxygen quantum yields. The core of this design involves using a highly tunable SubPz chromophore that shares its quasi-isolated ethene moiety with a DTE photoswitch.

Synthesis and photothermal conversion properties of sandwich N-fused porphyrin rhodium-μ-dichloride dimer complexes: π-extended analog of pentamethylcyclopentadienyl dirhodium(III)-μ-dichloride dimer

Anionic cyclopentadienyl (Cp) and its pentamethyl-substituted derivative (Cp*) serve as crucial ligands for creating stable π-coordinated materials, including catalysts. From a structural perspective, the π-extended analog of Cp, known as an N-fused porphyrin (NFP), is recognized as an intriguing 18π aromatic chromophore, offering near-infrared (NIR) optical properties that can be fine-tuned through metal complexation. When coordinated with rhodium at the central NFP core, it forms a sandwich binuclear rhodium(III) complex along with terminal and bridging chloride ligands, denoted as Rh-1, and its bromo derivative, Rh-1-Br. In contrast to the bis-NFP complex of iron(II) reported previously by our team, both Rh-1 and Rh-1-Br complexes exhibit strong NIR optical properties and narrow HOMO-LUMO energy gaps, attributed to minimal orbital interactions between the two co-facial NFP ligands. Leveraging these NIR absorption properties, we assessed the photothermal conversion properties of Rh-1 and ligand 1, revealing high conversion efficiency. This suggests their potential application as photothermal agents for use in photothermal therapy.

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.

Analysis of the Solvent Effects on the Crystal Growth of Peripherally Chlorinated Boron Subphthalocyanines

We report the characterization of the crystal/nano-structures for hexachloro-boron subphthalocyanines (Cl6BsubPc) grown via a variety of solvent diffusion methods and also with having axial substitutions variants: chloride; phenoxy; naphthoxy and...

Controlling Intramolecular Förster Resonance Energy Transfer and Singlet Fission in a Subporphyrazine-Pentacene Conjugate by Solvent Polarity

Due its complementary absorptions in the range of 450 and 600 nm, an energy-donating hexaaryl-subporphyrazine has been linked to a pentacene dimer, which acts primarily as an energy acceptor and secondarily as a singlet fission enabler. In the corresponding conjugate, efficient intramolecular Förster resonance energy transfer (i-FRET) is the modus operandi to transfer energy from the subporphyrazine to the pentacene dimer. Upon energy transfer, the pentacene dimer undergoes intramolecular singlet fission (i-SF), that is, converting the singlet excited state, via an intermediate state, into a pair of correlated triplet excited states. Solvatochromic fluorescence of the subporphyrazine is a key feature of this system and features a red-shift as large as 20 nm in polar media. Solvent is thus used to modulate spectral overlap between the fluorescence of subporphyrazine and absorption of the pentacene dimer, which controls the Förster rate constant, on one hand, and the triplet quantum yield, on the other hand. The optimum spectral overlap is realized in xylene, leading to Förster rate constant of 3.52×1011  s-1 and a triplet quantum yield of 171 % ±10 %. In short, the solvent polarity dependence, which is a unique feature of subporphyrazines, is decisive in terms of adjusting spectral overlap, ensuring a sizable Förster rate constant, and maximizing triplet quantum yields. Uniquely, this optimization can be achieved without a need for synthetic modification of the subporphyrazine donor.

Synthesis, Characterization and Optoelectronic Property of Axial-Substituted Subphthalocyanines

Two novel substituted subphthalocyanines have been prepared introducing m-hydroxybenzoic acid and m-hydroxyphenylacetic acid into the axial position of bromo-subphthalocyanine. The compounds have been characterized by Fourier transform infrared (FT-IR), Nuclear Magnetic Resonance (NMR) and single-crystal X-rays diffraction (XRD) methods. Their photophysical properties show that the axial substitution results into a relatively higher fluorescence quantum efficiency (ΦF=5.74 for m-hydroxybenzoic acid and 9.09 % for m-hydroxyphenylacetic acid) in comparison with that of the prototype compound, despite the almost negligible influence on the maximum absorption or the emission position. Moreover, the electrochemical behaviors show that the axial-substituted subphthalocyanines also exhibit enhanced specific capacitances of 395 F/g (m-hydroxybenzoic acid) and 362 F/g (m-hydroxyphenylacetic acid) compared with 342 F/g (the prototype) to the largest capacitance at the scan rate of 5 mV/s, and the significantly larger capacitance retentions of 83.6 % and 82.1 % versus 37.3 % upon density up to 3 A/g. These results show the potential of these axial-substituted subphthalocyanines in the use as organic photovoltaics and supercapacitors.

Oxidation-Induced Detachment of Ruthenoarene Units and Oxygen Insertion in Bis-Pd(II) Hexaphyrin π-Ruthenium Complexes

Two types of new bis-Pd(II) hexaphyrin π-ruthenium complexes are reported. A double-decker bis-Pd(II) hexaphyrin π-ruthenium complex 4 was obtained by oxidation-induced detachment of a ruthenoarene unit from the triple-decker complex 3 and oxygen-inserted triple-decker bis-Pd(II) hexaphyrin π-ruthenium complex 6 was obtained upon treatment of bis-Pd(II) [26]hexaphyrin 5 with [RuCl₂(p-cymene)]₂ under aerobic conditions. Although π-metal complexation of porphyrinoids often results in decreased global aromaticity due to the enhancement of local 6π aromatic segments, distinct aromatic characters were indicated for 4 and 6 by ¹H-NMR spectral and theoretical calculations. These results are accounted for in terms of possible resonance contributors of hexaphyrin di- and tetraanion ligands. Thus, π-metal coordination has been shown to be effective for modulation of the overall aromaticity.

Synthesis of 1,2-dicyanoferrocene by cyanation reactions

We report two synthetic pathways for the preparation of 1,2-dicyanoferrocene, in a search for new dinitrile-based precursors that could be useful in the synthesis of metallocene-containing azaporphyrins, as well as in catalysis. Both procedures include cyanation reactions as the key steps. Magnesiation of cyanoferrocene, followed by reaction with electrophilic tosyl cyanide, affords the target compound in only two synthetic steps from ferrocene. In addition, 1,2-dicyanoferrocene can be prepared by a three step procedure, which implies a twofold cyanation of 1,2-dibromoferrocene, using Zn(CN)[Formula: see text], in a biphasic medium and in the presence of bulky [Formula: see text]-BuXPhos-Pd-G3.

Expanding the Subporphyrazine Chromophore by Conjugation of Phenylene and Vinylene Substituents: Rainbow SubPzs

The efficiency of the vinylene moiety as a linker to intercommunicate the subporphyrazine (SubPz) core with other chromophores and redox active systems has been examined. In addition, different substitution patterns for hexaarylated SubPzs have been explored in order to control the absorption, fluorescence, and redox properties independently of one another. Besides X-ray crystallography, complete spectroscopic and electrochemical characterizations have been performed, and the conclusions have been supported by density functional theory calculations. The absorption and emission profiles, as well as the organization of the macrocycles in the crystalline state, are strongly determined by the substitution pattern. Within the hexaarylated family, para-substitution with electron-rich moieties (i.e., phenylene or ether) red-shifts both the SubPz absorption and emission bands. Progressive fading of these effects upon extending the oligophenylene branches from one to three units evidences the less efficient electronic delocalization over the phenyl ends as the oligophenylene branch is enlarged. Contrasting, meta-substitution produces little variation or blue shift of the SubPz Q-band, while bathochromic shifts are always observed for the emission bands. In hexavinylene-SubPzs, peripheral vinylene moieties adopt a coplanar configuration with the aromatic SubPz core, resulting in a π-extended chromophore that preserves the unique electronic tunability of SubPzs. This is reflected by the strong alteration of the SubPz electronic properties produced by phenyl and biphenyl moieties attached to the vinylene ends.

Two Discrete RuCp* (Cp*=Pentamethylcyclopentadienyl) Binding Modes of N-Confused Porphyrins: Peripheral π Complex and Sitting Atop Ruthenocenophane Complex by Skeletal Transformation

Complexation of a RuCp* cation with N-confused tetraarylporphyrins (NCPs) forms directly bound ruthenium(II) pentamethylcyclopentadienyl (Cp*) π-complex on a specific meso-aryl group (e.g., phenyl) neighboring peripheral imino nitrogen of NCPs in high yields. In contrast, in the case of NCPs bearing bulky meso-substituents (e.g., 3,5-di-tert-butylphenyl), new ruthenocenophane-like complex embedded on an N-confused calix[4]phyrin was formed through multiple C-H bond activation of methyl groups of Cp* ligand. The mechanistic insight into the formation of the ruthenocenophane was derived from DFT calculations.

Metallo-organic ensembles of tritopic subphthalocyanine ligands

Organic building blocks containing amines and aldehydes can be used for the preparation of complex metallo-organic structures, such as M[Formula: see text]L[Formula: see text] triple helicates or face-capped M[Formula: see text]L[Formula: see text] tetrahedral cages, through the formation of both dynamic covalent and coordinative linkages during the self-assembly process. Herein we describe how the subcomponent self-assembly method can be succesfully applied over a triamine-functionalized subphthalocyanine (SubPc) ligand to build metallo-supramolecular helicates. Two isomeric SubPcs (C[Formula: see text]-SubPc1 and C[Formula: see text]-SubPc1) have been prepared from the corresponding C[Formula: see text]-SubPcI[Formula: see text] and C[Formula: see text]-SubPcI[Formula: see text] precursors under optimized Suzuki conditions. We selected the tritopic C[Formula: see text]-SubPc1 derivative as ligand for the subcomponent self-assembly experiments, which involved the reaction with 2-formylpyridine and different Fe(II) salts. The self-assembly process was mainly studied by mass spectrometry (ESI direct injection techniques), and in all the conditions applied, we could observe the formation of helicate-type Fe[Formula: see text]SubPc[Formula: see text] structures and/or Fe[Formula: see text]SubPc[Formula: see text] species, which can be considered as open precursors of Fe[Formula: see text]SubPc[Formula: see text] tetrahedral cages.

A hindered subphthalocyanine that forms crystals with included aromatic solvent but will not play ball with C60

A novel subphthalocyanine containing bulky substituents placed at its peripheral sites (i.e. 2,3,9,10,16,17-hexa(2′,6′-di-iso-propylphenoxy)boron subphthalocyanine) was prepared and assessed for supramolecular binding with C[Formula: see text], through crystallisation and fluorescence studies. Three different crystal polymorphs of the subphthalocyanine were obtained that showed inclusion of a single aromatic solvent molecule within the well-defined cavity of the molecule but complete exclusion of C[Formula: see text]. Analysis of the crystal structures indicated that the bowl-shaped cavity of the subphthalocyanine molecule was only accessible to small molecules due to the steric congestion surrounding the macrocycle, which results in hindered rotation of the substituents on the NMR timescale. Enhanced solubility, up to 42.0 g/L in common organic solvents, was demonstrated consistent with the crystal structures which are dominated by relatively weak intermolecular interactions, which allow solvent molecules to play a role in crystallisation.

A Colorful Life: Scientific Achievements of Tomás Torres in the Fields of Phthalocyanines, Molecular Materials and Nanoscience

Some of the most important achievements of Tomás Torres in the last few decades within the fields of Phthalocyanines and related compounds, Molecular Materials and Nanoscience are revised and his recognized international prestige in these areas highlighted on the occasion of his 65th birthday.

The first porphyrin–subphthalocyaninatoboron(iii)-fused hybrid with unique conformation and intramolecular charge transfer behavior

The first porphyrin–subphthalocyaninatoboron(iii)-fused hybrid with unique conformation and intramolecular charge-transfer behaviour has been isolated and structurally characterized.

Cyclophanes containing bowl-shaped aromatic chromophores: three isomers of anti-[2.2](1,4)subphthalocyaninophane

The connection of bowl-shaped aromatic boron subphthalocyanines with anti-[2.2]paracyclophane resulted in the first observation of electronic communication between convex and concave surfaces. Three isomers of anti-[2.2](1,4)subphthalocyaninophane, described as concave-concave (CC), convex-concave (CV), and convex-convex (VV) according to the orientation of the subphthalocyanine units, were synthesized and characterized by various spectroscopic techniques, including (1) H NMR, electronic absorption, fluorescence, and magnetic circular dichroism spectroscopy and X-ray crystallography, together with molecular-orbital calculations. On going from the CC system to CV and further to VV, the Q band broadened and finally split as a result of through-space expansion of the conjugated systems, which were also reproduced theoretically.

Metallophthalocyanin-ocenes: scandium phthalocyanines with an η5-bound Cp ring

A series of scandium complexes supported by the phthalocyanine (Pc) ligand have been prepared and structurally characterized, including the first examples of η⁵-Cp metal phthalocyanines where the Cp fragment sandwiches the metal centre.

A core-expanded subphthalocyanine analogue with a significantly distorted conjugated surface and unprecedented properties

The introduction of a seven-membered-ring unit in the place of a five-membered-ring unit in the structure of subphthalocyanine resulted in significant distortion of the bowl-shaped structure of the conjugated molecule as well as the following unprecedented properties: the preferential formation of the axially fluoro substituted species, the fluttering-dynamic-motion-induced rapid exchange of P and M enantiomers, markedly split Q-band absorption, and a clear difference in the ring-current effects arising from the convex and concave surfaces.

Synthesis and spectroscopic properties of chiral binaphthyl-linked subphthalocyanines

Chiral binaphthyl-linked subphthalocyanines (SubPcs) have been prepared and characterized by various spectroscopies.

Structurally-modified subphthalocyanines: molecular design towards realization of expected properties from the electronic structure and structural features of subphthalocyanine

This feature article summarizes recent contributions of the authors in the synthesis of structurally-modified subphthalocyanines, which covers (1) modification of the conjugated system, (2) core-modification, and (3) exterior-modification.

Peripheral arylation of subporphyrazines

Peripherally hexaarylated subporphyrazines (SubPzs) have been prepared through a Pd-catalyzed, CuTC-mediated coupling of a hexaethylsulfanylated subporphyrazine with arylboronic acids. The introduced aryl substituents strongly influence the electronic properties of the subporphyrazine through effective conjugative interaction. Aryl rings endowed with π-electron-donating groups at the para positions produce a remarkable perturbation of the electron density of the SubPz macrocycle. This is reflected through significant redshifts of the SubPz CT and Q-bands, together with increase of the molar absorptivity of the former, with respect to those exhibited by the hexaphenyl-SubPz 2 a. Moreover, the trend in the first SubPz reduction potentials correlates with the Hammett constants (σp ) corresponding to the para substituents of the aryl. The domed, extended SubPz π-system self-assembles in the solid state to form a dimeric capsule that houses a solvent molecule.