Dimers, trimers and oligomers of phthalocyanines and related compounds

Unexpected Supramolecular-Induced Redox Switching in Sandwich Gd Bisphthalocyaninate

The redox state of the phthalocyanine in sandwich lanthanide complexes is crucial for their applications. In this work, we demonstrate that the cation-induced supramolecular assembly of crown-substituted phthalocyanine lanthanide complexes Ln[(15C5)4Pc]2 can be used to control the redox state of the ligand simultaneously with the coordination sphere of the central metal. We achieve unprecedented redox switching of phthalocyanine ligands in a double-decker Gd(III) complex, resulting from the intramolecular inclusion of potassium cations between the decks with simultaneous twisting of the ligands (the skew angle between them decreases from 44.61 to 0.21°). Such a structural change leads to an increase in the deck-to-deck distance and drastically facilitates ligand reduction. This process was shown to be anion-dependent: only potassium salts of weak acids (KOPiv and KOAc) induce intramolecular inclusion of cations with redox switching in contrast to salts of strong acids (KBr, KOPic, KSCN, and KPF6), where such a redox process does not occur. This breakthrough opens new avenues for controlling the electrochromic properties, of phthalocyanines, along with other properties, such as electrical conductivity, optics, etc.

π-Extended Pyrazinepyrene-Fused Zinc Phthalocyanines: Synthesis and Excited-State Charge Separation Involving Coordinated C60

A series of pyrazinepyrene-fused zinc phthalocyanines (ZnPc-Pyr_n) have been newly synthesized by reacting quinoxaline and the corresponding diamino-functionalized phthalocyanines as a new class of π-extended phthalocyanine systems. Bathochromically shifted absorption as a function of the number of pyrazinepyrene entities due to extended π-conjugation and quenched fluorescence due to the presence of fused pyrazinepyrene were witnessed. The electronic structures of these phthalocyanines were probed by systematic computational and electrochemical studies, while the excited-state properties were examined by pump-probe spectroscopies operating at the femto- and nanosecond time scales. Similar to the excited singlet lifetimes, the excited triplet states also revealed diminished lifetimes with an increased number of pyrazinepyrene entities. Further, the coordinatively unsaturated zinc in these molecules was coordinated with phenyl imidazole-functionalized fullerene, ImC₆₀, to form a new series of donor-acceptor conjugates. Upon full characterization of these conjugates, the occurrence of excited-state charge separation was established by transient pump-probe spectroscopy, covering wide temporal and spatial regions. The lifetime of the final charge-separated states was ∼2 ns and decreased with an increase in the number of fused pyrazinepyrene units.

Recent Progress for Single-Molecule Magnets Based on Rare Earth Elements

Single-molecule magnets (SMMs) have attracted much attention due to their potential applications in molecular spintronic devices. Rare earth SMMs are considered to be the most promising for application owing to their large magnetic moment and strong magnetic anisotropy. In this review, the recent progress in rare earth SMMs represented by mononuclear and dinuclear complexes is highlighted, especially for the modulation of magnetic anisotropy, effective energy barrier (U_eff) and blocking temperature (T_B). The terbium- and dysprosium-based SMMs have a U_eff of 1541 cm^-1 and an increased T_B of 80 K. They break the boiling point temperature of liquid nitrogen. The development of the preparation technology of rare earth element SMMs is also summarized in an overview. This review has important implications and insights for the design and research of Ln-SMMs.

DNA groove binder and significant cytotoxic activity on human colon cancer cells: Potential of a dimeric zinc (II) phthalocyanine derivative

The interaction of a multi-component system consisting of benzene-1,4-diyldimethanimine-bridged dimeric zinc-phthalocyanine groups (4OMPCZ) with calf thymus DNA (ct-DNA) was investigated using UV-Vis absorption, fluorescence emission spectroscopy methods, and viscosity measurements. The binding constant, K_b, which is an important parameter to gain information about the binding mode, was found as 9.7 × 10⁷ M^-1 from the UV-Vis absorption studies. Another important spectrophotometric tool is competitive displacement assays with Ethidium bromide and Hoechst 33342. Through this experiment, a higher K_SV value was obtained with Hoechst for the phthalocyanine derivative, 4OMPCZ, and the ct-DNA complex than with ethidium bromide. Additionally, molecular docking studies were conducted to calculate the theoretical binding constant and visualize the interactions of 4OMPCZ with a model DNA. According to docking results, although the interactions are mainly located in the major groove of the DNA helix, due to the wrapping, these interactions can also be extended to the minor groove of the DNA. Spectrophotometric, molecular docking, and viscosity studies revealed that the interaction of 4OMPCZ with DNA is likely to be via the major and minor grooves. The in vitro cytotoxic activity of 4OMPCZ was evaluated by MTT assay on human colon cancer cells (HT29) after 72 h of treatment. 4OMPCZ indicated significant cytotoxic activity when stimulated with UV light compared to the standard chemotherapy drugs, fluorouracil (5-FU), and cisplatin on HT29 colon cancer cells. The IC₅₀ value of 4OMPCZ displayed considerably lower concentrations compared to the standard drugs, 5-FU, and cisplatin.

Effects of aggregation on the structures and excited-state absorption for zinc phthalocyanine

In the present paper, the aggregated structures of zinc phthalocyanine (ZnPc) have been investigated by considering its dimers and trimers. Based on the density functional theory calculations, two stable conformations are obtained for the ZnPc dimer and trimer, respectively. The IGMH (independent gradient model based on the Hirshfeld partition of molecular density) analysis reveals that the π-π interaction between the ZnPc molecules causes the aggregation. Normally, stacked structures with a slight displacement are favorable for aggregation. In addition, the planar structure of the ZnPc monomer is largely maintained in the aggregated conformations. For the presently obtained structures, the first singlet excited state absorption (ESA) spectra of these aggregated conformations of ZnPc were calculated based on the linear-response time-dependent density functional theory (LR-TDDFT), which has been well applied by our group. The results of the excited state absorption spectra reveal that the aggregation causes the ESA band to blue shift compared to the ZnPc monomer. By using the conventional description of the interaction between monomer transition dipoles, this blue shift is elucidated by the side-by-side transition dipole moments in the constituted monomers. The present results for the ESA combined with the previously reported results for ground state absorption (GSA) will provide guidelines to tune the window of the optical-limiting effect for the ZnPc based materials.

Lanthanide-tetrapyrrole complexes: synthesis, redox chemistry, photophysical properties, and photonic applications

Tetrapyrrole derivatives such as porphyrins, phthalocyanines, naphthalocyanines, and porpholactones, are highly stable macrocyclic compounds that play important roles in many phenomena linked to the development of life. Their complexes with lanthanides are known for more than 60 years and present breath-taking properties such as a range of easily accessible redox states leading to photo- and electro-chromism, paramagnetism, large non-linear optical parameters, and remarkable light emission in the visible and near-infrared (NIR) ranges. They are at the centre of many applications with an increasing focus on their ability to generate singlet oxygen for photodynamic therapy coupled with bioimaging and biosensing properties. This review first describes the synthetic paths leading to lanthanide-tetrapyrrole complexes together with their structures. The initial synthetic protocols were plagued by low yields and long reaction times; they have now been replaced with much more efficient and faster routes, thanks to the stunning advances in synthetic organic chemistry, so that quite complex multinuclear edifices are presently routinely obtained. Aspects such as redox properties, sensitization of NIR-emitting lanthanide ions, and non-linear optical properties are then presented. The spectacular improvements in the quantum yield and brightness of Yb^III-containing tetrapyrrole complexes achieved in the past five years are representative of the vitality of the field and open welcome opportunities for the bio-applications described in the last section. Perspectives for the field are vast and exciting as new derivatizations of the macrocycles may lead to sensitization of other Ln^III NIR-emitting ions with luminescence in the NIR-II and NIR-III biological windows, while conjugation with peptides and aptamers opens the way for lanthanide-tetrapyrrole theranostics.

Zinc-[7]helicenocyanine and Its Discrete π-Stacked Homochiral Dimer

In this communication, we demonstrate a novel approach to prepare a discrete dimer of chiral phthalocyanine (Pc) by exploiting the flexible molecular geometry of helicenes, which enables structural interlocking and strong aggregation tendency of Pcs. Synthesized [7]helicene‐Pc hybrid molecular structure, zinc‐[7]helicenocyanine (Zn‐7HPc), exclusively forms a stable dimeric pair consisting of two homochiral molecules. The dimerization constants were estimated to be as high as 8.96×10⁶ M⁻¹ and 3.42×10⁷ M⁻¹ in THF and DMSO, respectively, indicating remarkable stability of dimer. In addition, Zn‐7HPc exhibited chiral self‐sorting behavior, which resulted in preferential formation of a homochiral dimer also in the racemic sample. Two phthalocyanine subunits in the dimeric form strongly communicate with each other as revealed by a large comproportionation constant and observation of an IV‐CT band for the thermodynamically stable mixed‐valence state.

Synthesis and characterization of heteroleptic rare earth double-decker complexes involving tetradiazepinoporphyrazine and phthalocyanine macrocycles

Reaction of (2,3,9,10,16,17,23,24-octabutylphthalocyaninato)lanthanide(iii) acetylacetonates (BuPcLn(acac), 1a-c, Ln = Lu (a), Eu (b), La (c)) with a tetrakis(5,7-bis(4-tert-butylphenyl)-6H-1,4-diazepino)[2,3-b,g,l,q]porphyrazine ligand (tBuPhDzPzH2, 2) produced sandwich compounds (tBuPhDzPz)Ln(BuPc) (3a-c), which represent the first heteroleptic double-deckers incorporating both Pc and DzPz decks. A combination of high-resolution mass spectrometry, UV-Vis/NIR, MCD, and 1H NMR spectroscopy, and square-wave voltammetry provided unambiguous characterization of target complexes 3 indicating that their spectral and electrochemical properties are generally intermediate with respect to their homoleptic relatives. Based on the data of solution-state 1H-1H NMR (COSY, NOESY) correlation spectroscopy supported by DFT calculations, a dimerization tendency of compounds 3 proportional to the Ln(iii) ion size was found. The spectroelectrochemical study of 3 and the corresponding homoleptic double-deckers revealed a pronounced tendency to aggregation of the one-electron oxidized forms of DzPz-containing double-decker complexes compared to homoleptic Pc2Ln compounds.

Synthesizing and evaluating the photodynamic efficacy of asymmetric heteroleptic A7B type novel lanthanide bis-phthalocyanine complexes

In this study heteroleptic A₇B type novel Lu(iii) and Eu(iii) lanthanide phthalocyanines (LnPc(Pox)[Pc′(AB₃SH)]) with high extinction coefficients have been synthesized as candidate photosensitizers with reaction yields higher than 33%. The singlet oxygen quantum yields of LuPc(Pox)[Pc′(AB₃SH)] and EuPc(Pox)[Pc′(AB₃SH)], respectively, were measured 17% and 1.4% by the direct method in THF. The singlet oxygen quantum yield of LuPc(Pox)[Pc′(AB₃SH)] in THF is the highest among lutetium(iii) bis-phthalocyanine complexes to date. The photodynamic efficacy of the heteroleptic lanthanide phthalocyanines was evaluated by measuring cell viabilities of A549 and BEAS-2B lung cells, selected to representing in vitro models for testing cancer and normal cells against potential drugs. The cell viabilities demonstrated concentration dependent behavior and were varied by the type of phthalocyanines complexes. Irradiation of the cells for 30 minutes with LED array at 660 nm producing flux of 0.036 J cm⁻² s⁻¹ increased cell death for LuPcPox-OAc, LuPc(Pox)[Pc′(AB₃SH)] and ZnPc. The IC₅₀ concentrations of LuPc(Pox)[Pc′(AB₃SH)] and ZnPc were determined to be below 10 nM for both cell lines, agreeing very well with the singlet oxygen quantum yield measurements. These findings suggest that LuPc(Pox)[Pc′(AB₃SH)] and particularly LuPcPox-OAc are promising drug candidates enabling lowered dose and shorter irradiation time for photodynamic therapy.

Novel bis-lanthanide Lu(iii) and Eu(iii) phthalocyanine complexes have been designed/synthesized and tested their photodynamic efficacy for A549 and BEAS-2B cells in vitro conditions as candidate photosensitizers in PDT.

Antiferromagnetic coupling in copper(II)porphyrin dimers linked by copper(II) or palladium(II) ion

The synthesis of porphyrin dimers linked by metal ions is described and the X-ray structure of two new dimers is presented. As previously shown for diamagnetic metal ions, strong electronic interactions between the individual subunits were observed. Antiferromagnetic coupling between copper(II)porphyrins linked by palladium(II) or copper(II) ions was studied by EPR and SQUID measurements. For the palladium(II)-linked dimer, the very small antiferromagnetic coupling was estimated by EPR measurements ([Formula: see text] <-1 cm[Formula: see text]. For the trinuclear-copper(II)-linked dimer, a large antiferromagnetic coupling between the copper(II) ions was measured. In this trinuclear compound, the linking copper(II) ion is used as a relay to increase the interaction between the two copper(II)porphyrins.

Extreme multi-point van der Waals interactions: isolable dimers of phthalocyanines substituted with pillar-like azaacenes

How strong are van der Waals interactions in determining the final outcome of self-assembled structures of small molecular systems? Herein we report isolable phthalocyanine (Pc) dimers bound by π-π interactions between monomeric Pcs which can be handled as single entities. Pc dimers have been continuously investigated as one of the simplest models of Pc aggregates. Pcs were substituted with eight dihydrodiazapentacene (DHDAP) moieties on the periphery, which act as pillar-like π-planes and these molecules form H-type dimers with the help of synergetic π-π interactions between two co-facial Pc rings and among the pillar-like DHDAP moieties. The dimer structures were fully confirmed by 1D and 2D NMR, ESR, and electronic absorption measurements. The dissociation of these dimers was observed in particular solvents such as o-dichlorobenzene, due to the good solubility of the larger π-conjugated molecules. On the other hand, in ethyl acetate the monomers were metastable species and underwent selective dimerization. Interestingly in THF, neither the dimerization of the monomers nor the dissociation of dimers was observed, suggesting that both the dimers and the monomers were kinetically well stabilized. For hours to days, we can handle these dimers as "a molecule" not only in solution but also even in mass spectrometry under ionization conditions without significant dissociation.

Photodynamic properties of aza-analogues of phthalocyanines

Spectral and photophysical properties and in vitro photodynamic activity of aza-analogues of phthalocyanines are summarized.

Synthesis, characterization, and optical and surface properties of (4-(trifluoromethylthio)phenoxy) copper(ii) phthalocyanine

This paper reports on the synthesis and characterization of a non-peripherally tetra-substituted copper phthalocyanine containing a 4-(trifluoromethylthio)phenoxy group.

Selective Stabilization of the Spin States of a Magnetically Anisotropic Dysprosium Ion Induced by Photo-Excitation of the Associated Cyclic π-Conjugated System

The presence of a new electronic interaction, which couples a 4 f-electronic system with a total angular momentum J and a photoexcited cyclic π-conjugated system with an orbital angular momentum L, in the bis(phthalocyaninato)dysprosium single-molecule magnet ([DyPc₂ ]^- ) is reported. Two π-π* excited states in the visible spectral region of the [DyPc₂ ]^- complex, which are denoted here as Q_L and Q_H , showed significantly different temperature and field dependences of the magnetic circular dichroism (MCD) A-term intensity. This phenomenon not only indicates the presence of a "J-L" interaction, but also that the interaction generates two different preferred orientations of the J-L pair, either parallel (for the Q_H band) or antiparallel (for the Q_L band), depending on the excitation energy. We have constructed a theoretical model that reproduces the temperature and field dependences, and quantitatively evaluated the J-L interaction.

Conceptual design of tetraazaporphyrin- and subtetraazaporphyrin-based functional nanocarbon materials: electronic structures, topologies, optical properties, and methane storage capacities

A large variety of conceptual three- and fourfold tetraazaporphyrin- and subtetraazaporphyrin-based functional 3D nanocage and nanobarrel structures have been proposed on the basis of in silico design. The designed structures differ in their sizes, topology, porosity, and conjugation properties. The stability of nanocages of Oh symmetry and nanobarrels of D4h symmetry was revealed on the basis of DFT and MD calculations, whereas their optical properties were assessed using a TDDFT approach and a long-range corrected LC-wPBE exchange-correlation functional. It was shown that the electronic structures and vertical excitation energies of the functional nanocage and nanobarrel structures could be easily tuned via their size, topology, and the presence of bridging sp(3) carbon atoms. TDDFT calculations suggest significantly lower excitation energies in fully conjugated nanocages and nanobarrels compared with systems with bridging sp(3) carbon fragments. Based on DFT and TDDFT calculations, the optical properties of the new materials can rival those of known quantum dots and are superior to those of monomeric phthalocyanines and their analogues. The methane gas adsorption properties of the new nanostructures and nanotubes generated by conversion from nanobarrels were studied using an MD simulation approach. The ability to store large quantities of methane (106-216 cm(3) (STP) cm(-3)) was observed in all cases with several compounds being close to or exceeding the DOE target of 180 cm(3) (STP) cm(-3) for material-based methane storage at a pressure of 3.5 MPa and room temperature.

ABAB-type phthalocyanines simultaneously bearing electron donating and electron accepting groups. Synthesis, spectroscopy, and structure

Mg(trans-TPTCPc) was successfully prepared and structurally characterized, representing the first structurally characterized ABAB-type phthalocyanine compound simultaneously bearing electron-donating and electron-accepting groups.

Synthesis and electronic properties of nitrogen-bridged dimers of boron subphthalocyanines

We describe for the first time the synthesis and characterization of a new family of subphthalocyanine derivatives, the μ-azo dimers, in which two closely interacting macrocycles are axially linked together by a B–N–B bridge.

New developments in porphyrin-like macrocyclic chemistry: a novel family of dibenzotetraaza[14]annulene-based cofacial dimers

The first known cofacial dimers, based on covalently linked dibenzotetraaza[14]annulenes, were synthesized in reasonable 35–40% yields, without recourse to high-dilution techniques.

Electrochemical properties of carbonyl substituted phthalocyanines as electrode materials for lithium-ion batteries

Through I₂doping and foam nickel coating technology, the conductivity and electrochemical properties of phthalocyanines (2and3) have been improved obviously.

Double-decker bis(tetradiazepinoporphyrazinato) rare earth complexes: crucial role of intramolecular hydrogen bonding

Study focuses on specific interactions in diazepine-containing macroheterocycles.

Intramolecular aggregation and optical limiting properties of triazine-linked mono-, bis- and tris-phthalocyanines

A series of triazine-linked mono-, bis- and tris-phthalocyanines are synthesized, intramolecular aggregation is found in bis- and tris-phthalocyanines via π-π stacking interaction. Theoretical and experimental studies reveal the formation of the intramolecular aggregation. The spectrographic, photophysical and nonlinear optical properties of these compounds are adjusted for the formation of the intramolecular aggregation. The bis-phthalocyanine dimer presents smaller fluorescence quantum yield, lower triplet formation yield and the triplet-minus-ground state extinction coefficient, which causes poorer optical limiting performance. It is interesting that the tris-phthalocyanine is composed of a mono-phthalocyanine part and a bis-phthalocyanine part, the optical limiting property of the tris-phthalocyanine is similar to that of mono-phthalocyanine.

DFT and TD-DFT calculations of axially substituted tin porphyrins and an ethynyl-linked tin porphyrin dimer

Time-dependent density functional theory calculations have been employed to characterize the inter-macrocycle interactions introduced when two tin(IV) porphyrins are axially covalently bonded via an ethynyl linker. The effect of changing the relative orientations of the two metalloporphyrin macrocycles is explored, with particular attention given to electronic states at energies up to the Soret-correlated states in the dimer. Expansion of the Gouterman four orbital approach for the monomer to an eight orbital approach in the dimer produces a satisfactory analysis. The results are used to examine the feasibility of using such linked structures in photon harvesting schemes.

meso-Phenyltetrabenzotriazaporphyrin based double-decker lanthanide(iii) complexes: synthesis, structure, spectral properties and electrochemistry

A series of tetrabenzotriazaporphyrin half-sandwich and sandwich compounds, including unexpected meso-dearylated derivatives as well as the first triple-decker, have been prepared.

Synthesis and magnetic properties of an annulated dinuclear copper(II) phthalocyanine peripherally having 2,6-dimethylphenoxy substituents

A dinuclear copper(II) phthalocyanine complex with 12 2,6-dimethylphenoxyl groups at the peripheral positions of the [ CuPc ]2 framework, where [ CuPc ] units are linked by a common annulated benzene ring to give the planar dinuclear structure, was prepared and characterized. The introduced bulky 2,6-dimethylphenoxyl groups were revealed to effectively suppress the aggregation of the dinuclear complex in the toluene solution, showing a considerably red-shifted Q-band at 838 nm. The EPR spectrum (measured in the frozen toluene solution at 15 K) and temperature-dependent magnetic moment indicated the existence of antiferromagnetic interaction between the copper(II) ions. The exchange integral J was estimated to be -1.8 cm-1 using Bleaney Bowers equation for the S1 = S2 = 1/2 system. The long-range interaction ( Cu – Cu distance = 10.7 Å) through the common annulated benzene ring between two [ CuPc ] units was confirmed by the DFT calculation result.

A phthalocyanine-subphthalocyanine heterodinuclear dimer: comparison of spectroscopic properties with those of homodinuclear dimers of constituting units

A phthalocyanine-subphthalocyanine heterodinuclear dimer has been disclosed for the first time with its unique flat-bowl-shaped structure revealed by X-ray crystallography. Its spectroscopic properties were compared with those of homodinuclear dimers of constituting units, as well as those of constituting monomeric units.

Indium-chlorine and gallium-chlorine tetrasubstituted phthalocyanines in a bulk system, Langmuir monolayers and Langmuir-Blodgett nanolayers--spectroscopic investigations

The paper deals with spectroscopic characterization of metallic phthalocyanines (Pc's) (indium and gallium) complexed with chlorine and substituted with four benzyloxyphenoxy peripheral groups in bulk systems, 2D Langmuir monolayers and Langmuir-Blodgett nanolayers. An influence of the molecular structure of dyes (the presence of metal and of substitutes attached to the phthalocyanine macroring) on the in situ measurements of light absorption is reported. Molecular arrangement of the phthalocyanine molecular skeleton in the Langmuir monolayers on water substrate and in the Langmuir-Blodgett nanolayers is evaluated. A comparison of the light absorption spectra of the phthalocyanine monolayers with the spectra of the dyes in solution supports the existence of dye aggregates in the monolayer. It was shown that the type of dye aggregates (oblique and H types) depends markedly on the dye molecular structures. The NIR-IR, IR reflection-absorption and Raman spectra are also monitored for Langmuir-Blodgett nanolayers in non-polarized and polarized light. It was shown that the dye molecules in the Langmuir-Blodgett layers are oriented nearly vertically with respect to a gold substrate.