A Molecular Chameleon: Reversible pH- and Cation-Induced Control of the Optical Properties of Phthalocyanine-Based Complexes in the Visible and Near-Infrared Spectral Ranges

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.

Electrochromic Smart Window Based on Transition-Metal Phthalocyanine Derivatives

Phthalocyanines have been widely investigated as electrochromic materials because of their large conjugated structure. However, they have shown limited applicability due to their complex electrochromism mechanism and low solubility in common organic solvents. Replacement of central metal ions in phthalocyanines affects their stability and is responsible for various electrochromic phenomena, such as color change. Herein, the relationship between the electron d-orbital arrangement in the outermost layer of transition metals and the electrochromic stability of phthalocyanine derivatives has been investigated. An enhanced solubility of phthalocyanines in organic solvents was obtained through the introduction of quaternary tert-butyl substitution. Electrochromic devices fabricated with transition-metal phthalocyanine derivatives showed high response speeds and good stability. The fast color-switching feature between blue/green and blue/purple makes it a promising candidate for smart windows and adaptive camouflage applications.

A new highly Selective, sensitive and NIR spectrophotometric probe based on A2B2-Type of unsymmetrical phthalocyanine for hazardous Be2+ recognition

The aim of this work is to construct a new A₂B₂-type of unsymmetrical and ratiometric phthalocyanine (Pc) based-probe O-A₂B₂ZnPc to provide an effective solution to critical inadequacy to be experienced for the detection of hazardous Be²⁺. O-A₂B₂ZnPc enabling strong absorption and emission in Near-Infrared region (λ_abs-λ_em wavelengths of 694-712 nm) showed excellent selectivity and sensitivity toward Be²⁺ among competitive metal ions by both spectrophotometric and fluorometric methods. The probe with oligomeric Pc form in THF was degraded with the addition of aqueous Be²⁺ and arranged to J-aggregation form, resulting in a remarkably diminishing in Q-band at 694 nm as well as a new band formation at 746 nm, and a considerably decreasing in fluorescence emission. The probe has superior features for the determination of Be²⁺ such as high quantum efficiency and photochemical stability, rapid response (1 s), high selectivity and very low Limit of Detection (0.26 ppb and 1.5 ppb) for UV-Vis and fluorescence, respectively which are quite good values according to the permissible amount of Be²⁺ (4 ppb) in water as specified by World Health Organization. O-A₂B₂ZnPc can be shown among the best performing probes with its unique properties according to previous studies in the literature. In addition, the geometrical and spectral features of the O-A₂B₂ZnPc were analyzed in detail by DFT calculations.

Drug Molecular Immobilization and Photofunctionalization of Calcium Phosphates for Exploring Theranostic Functions

Theranostics (bifunction of therapeutics and diagnostics) has attracted increasing attention due to its efficiency that can reduce the physical and financial burden on patients. One of the promising materials for theranostics is calcium phosphate (CP) and it is biocompatible and can be functionalized not only with drug molecules but also with rare earth ions to show photoluminescence that is necessary for the diagnostic purpose. Such the CP-based hybrids are formed in vivo by interacting between functional groups of organic molecules and inorganic ions. It is of great importance to elucidate the interaction of CP with the photofunctional species and the drug molecules to clarify the relationship between the existing state and function. Well-designed photofunctional CPs will contribute to biomedical fields as highly-functional ormultifunctional theranostic materials at the nanoscales. In this review, we describe the hybridization between CPs and heterogeneous species, mainly focusing on europium(III) ion and methylene blue molecule as the representative photofunctional species for theranostics applications.

Rare-earth based tetrapyrrolic sandwiches: chemistry, materials and applications

This review summarises advances in chemistry of tetrapyrrole sandwiches with rare earth elements and highlights the current state of their use in single-molecule magnetism, organic field-effect transistors, conducting materials and nonlinear optics.

A sextuple-decker heteroleptic phthalocyanine heterometallic samarium-cadmium complex with crystal structure and nonlinear optical properties in solution and gel glass

A sextuple-decker heteroleptic phthalocyanine heterometallic compound (1) with a subunit arrangement of {(Pc)Sm(Pc)Cd(Pc*)Cd(Pc*)Cd(Pc)Sm(Pc)} has been prepared and analyzed using various spectroscopic instruments, in which four unsubstituted phthalocyanine anions (Pc) and two substituted analogues (Pc*) with n-pentoxyl substituents at eight peripheral positions are connected through the complexation of two Sm(III) and three Cd(II) ions. In particular, its sextuple-decker structure has been disclosed by the single-crystal X-ray diffraction technique. The solution and gel glass forms of this compound display third-order nonlinear optical properties due to the intrinsic conjugated nature over the sextuple-decker sandwich complex.

Near infrared photothermal conversion materials: mechanism, preparation, and photothermal cancer therapy applications

Photothermal therapy (PTT) has been widely applied in cancer therapy as a result of its non-invasive, localized treatment and good therapeutic effect. In general, the final therapeutic effect of PTT mainly depends on the photothermal materials, which can be further considered to be determined by the photothermal conversion efficiency, biocompatibility, and photothermal stability of photothermal materials. In this review, photothermal materials including inorganic materials, organic materials, and organic-inorganic composite materials in recent years have been summarized in terms of the mechanism, preparation, and cancer therapy applications. In the end, the perspectives and obstacles in their further development are overviewed.

Tetra-(benzo-24-crown-8)-phthalocyanines as a platform for supramolecular ensembles: Synthesis and interaction with viologen

The synthesis of a series of novel tetra-(benzo-24-crown-8)-phthalocyanines (Mg(II), Ni(II) and Co(II)) as well as a modified procedure for the free-base ligand and its Zn(II) and Cu(II) complexes are reported. The tendency of these phthalocyanines to undergo supramolecular cofacial dimerization induced by interaction with a viologen ([Formula: see text]-di(but-3-ynyl)-4,4[Formula: see text]-bipyridinium) was investigated by UV-vis absorption and EPR spectral studies in solution. The nature of the metal cation in phthalocyanine, the concentration, as well as the solvent all influenced the assembly processes.

α- and β-Substituted Metal-Free Phthalocyanines: Synthesis, Photophysical and Electrochemical Properties

Two novel phthalonitrile derivatives, bearing two hexyloxy groups and a benzodioxin (or a naphthodioxin) annulated ring, along with their corresponding metal-free phthalocyanines (H2Pc) were prepared. FT-IR, mass, electronic absorption, 1H NMR, and 13C NMR spectroscopy were employed for the characterization of all compounds. The effect of hexadeca substituents on the photophysical properties of metal-free Pcs was investigated. Photophysical properties of H2Pc were studied in tetrahydrofuran (THF). Fluorescent quantum yields of phthalocyanines (Pcs) were calculated and compared with the unsubstituted phthalocyanine. 1,4-Benzoquinone effectively quenched the fluorescence of these compounds in THF. Cyclic and square wave voltammetry methods were applied to metal-free phthalocyanines and Pc-centered oxidation and reduction processes were obtained.

Novel 2-naphthyl substituted zinc naphthalocyanine: synthesis, optical, electrochemical and spectroelectrochemical properties

New zinc naphthalocyanine with bulky 2-naphthyl groups was obtained. Aggregation drastically influences its optical and electrochemical behavior. Spectroelectrochemistry helps to establish the oxidation potential and reveals unusual color change.

Carbene insertion to N–H bonds of 2-aminothiazole and 2-amino-1,3,4-thiadiazole derivatives catalyzed by iron phthalocyanine

Iron(III) phthalocyaninate decorated with crown ether substituents, [(15C5)4PcFe]Cl, efficiently catalyzed the insertion of carbene derived from ethyl diazoacetate to six amines functionalized with thiazole, thiazoline and thiadiazole heterocycles. The reactions were carried out under practical conditions using EDA:amine stoechiometric ratio with 0.05 mol% catalyst loading. Turnover numbers up to 3360 have been achieved. The aminoacid derivatives bearing heterocyclic moieties were obtained under catalytic conditions for the first time with 36–69% yields in the case of single N–H insertion products and up to 77% in the case of double N–H insertion products.

Methodological Survey of Simplified TD-DFT Methods for Fast and Accurate Interpretation of UV-Vis-NIR Spectra of Phthalocyanines

A methodological survey of density functional theory (DFT) methods for the prediction of UV-visible (vis)-near-infrared (NIR) spectra of phthalocyanines is reported. Four methods, namely, full time-dependent (TD)-DFT and its Tamm-Dancoff approximation (TDA), together with their simplified modifications (sTD-DFT and sTDA, respectively), were tested by using the examples of unsubstituted and alkoxy-substituted metal-free ligands and zinc complexes. The theoretical results were compared with experimental data derived from UV-visible absorption and magnetic circular dichroism spectroscopy. Seven popular exchange-correlation functionals (BP86, B3LYP, TPSSh, M06, CAM-B3LYP, LC-BLYP, and ωB97X) were tested within these four approaches starting at a relatively modest level using 6-31G(d) basis sets and gas-phase BP86/def2-SVP optimized geometries. A gradual augmentation of the computational levels was used to identify the influence of starting geometry, solvation effects, and basis sets on the results of TD-DFT and sTD-DFT calculations. It was found that although these factors do influence the predicted energies of the vertical excitations, they do not affect the trends predicted in the spectral properties across series of structurally related substituted free bases and metallophthalocyanines. The best accuracy for the gas-phase vertical excitations was observed in the lower-energy Q-band region for calculations that made use of range-separated hybrids for both full and simplified TD-DFT approaches. The CAM-B3LYP functional provided particularly accurate results in the context of the sTD-DFT approach. The description of the higher-energy B-band region is considerably less accurate, and this demonstrates the need for further advances in the accuracy of theoretical calculations. Together with a general increase in accuracy, the application of simplified TD-DFT methods affords a 2-3 orders of magnitude speedup of the calculations in comparison to the full TD-DFT approach. It is anticipated that this approach will be widely used on desktop computers during the interpretation of UV-vis-NIR spectra of phthalocyanines and related macrocycles in the years ahead.

Non-peripherally alkylamino-substituted phthalocyanines: Synthesis, spectral, photophysical and acid-base properties

Non-peripherally substituted metal-free and zinc phthalocyanines (Pcs) bearing four diethylamino groups and four Br atoms were prepared. Optimal conditions for synthesis of corresponding precursor ([Formula: see text] 3-bromo-6-(diethylamino)phthalonitrile) either by nucleophilic substitution or by Buchwald–Hartwig coupling were studied. Noteworthy, 3,6-bis(diethylamino)phthalonitrile was also formed, nevertheless only at low yield (typically below 1%) and all attempts for its cyclotetramerization failed. Q bands of prepared Pcs were strongly red shifted up to the near-IR region (769 and 800 nm in THF for zinc and metal-free Pc, respectively). Unusually large hypsochromic shifts of the Q bands, 130 and 80 nm for metal-free and zinc Pc, respectively, were observed upon treating these Pcs with trifluoroacetic acid, which was attributed to the protonation of non-peripheral amines. Treatment with sulfuric acid led to subsequent protonation on the azomethine nitrogens as well. Photophysical study revealed low fluorescence emission of both derivatives ([Formula: see text] <0.03, in THF) and efficient singlet oxygen production only for zinc Pc ([Formula: see text] 0.77 in THF and 0.60 in DMF).

Crown-substituted naphthalocyanines: synthesis and supramolecular control over aggregation and photophysical properties

Tetra-15-crown-5-naphthalocyanines as first representatives of crown-substituted π-extended phthalocyanines were synthesized and characterized. The possibility to control their aggregation and photophysical properties by reversible formation of supramolecular assemblies in the presence of KOAc was demonstrated.

Super-Sensitive Protonation Behavior of Trifluoroethoxy-Substituted Phthalocyanines and Their Application to Solvent Discrimination

The super-sensitive protonation behavior of trifluoroethoxy-substituted phthalocyanines (TFEO-Pcs) was carefully studied using UV-vis and fluorescence spectroscopy, as well as computational calculations. The practical utility of TFEO-Pcs in sensor technology was demonstrated by identifying chloroform samples from different commercial sources.

Ring-Oxidized Zinc(II) Phthalocyanine Cations: Structure, Spectroscopy, and Decomposition Behavior

A bromonium oxidizing agent was used to produce a ring-oxidized zinc phthalocyanine (PcZn), [PcZn(solvent)]^•₂[BAr^F₄]₂ (1·solvent), in good yield. This material is dimeric in the solid state with one axially coordinated solvent [tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME)] and close intradimer ring-ring distances of 3.18 and 3.136 Å (THF and DME respectively); this proximity facilitates strong antiferromagnetic coupling to yield diamagnetic dimers. 1·THF is present in solution as a monomer and a dimer. In CH₂Cl₂, the dimer is favored above 0.1 mM, and it is almost exclusively present in solvents with a high dielectric constant such as acetonitrile. The material 1·THF/DME decomposes in DME to a meso-nitrogen-protonated species, [HPcZn(DME)₂][BAr^F₄] (2), which was isolated and represents the first example of such a structurally characterized, protonated, unsubstituted PcM complex. A partially oxidized dimer or "pimer" [(PcZn(DME))₂]^•[BAr^F₄] (3) was also structurally characterized and has a intradimer ring-ring distance of 3.192 Å, similar to 1·THF/DME. Dimer 3 also represents the first isolated PcM-based pimer. Electron paramagnetic resonance analysis of a 1.0 mM solution of 1·DME in DME showed the production of 3 over hours by the combination of 1·DME and 2 in solution.

Organic Dye Based Nanoparticles for Cancer Phototheranostics

Phototheranostics, which simultaneously combines photodynamic and/or photothermal therapy with deep-tissue diagnostic imaging, is a promising strategy for the diagnosis and treatment of cancers. Organic dyes with the merits of strong near-infrared absorbance, high photo-to-radical and/or photothermal conversion efficiency, great biocompatibility, ready chemical structure fine-tuning capability, and easy metabolism, have been demonstrated as attractive candidates for clinical phototheranostics. These organic dyes can be further designed and fabricated into nanoparticles (NPs) using various strategies. Compared to free molecules, these NPs can be equipped with multiple synergistic functions and show longer lifetime in blood circulation and passive tumor-targeting property via the enhanced permeability and retention effect. In this article, the recent progress of organic dye-based NPs for cancer phototheranostic applications is summarized, which extends the anticancer arsenal and holds promise for clinical uses in the near future.

π-Extended hexadeca-substituted cobalt phthalocyanine as an active layer for organic field-effect transistors

The structural modification of the phthalocyanine skeleton with a hexadeca substitution pattern is a promising approach for the fabrication of active layers for OFETs.

Evaluation of the Intramolecular Charge-Transfer Properties in Solvatochromic and Electrochromic Zinc Octa(carbazolyl)phthalocyanines

2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato zinc(II) (3) and 2,3,9,10,16,17,23·24-octakis-(3,6-di-tert-butyl-9H-carbazole) phthalocyaninato zinc(II) (4) complexes were prepared and characterized by NMR and UV-vis spectroscopies, magnetic circular dichroism (MCD), matrix-assisted laser desorption ionization mass spectrometry, and X-ray crystallography. UV-vis and MCD data are indicative of the interligand charge-transfer nature of the broad band observed in 450-500 nm range for 3 and 4. The redox properties of 3 and 4 were probed by electrochemical and spectro-electrochemical methods, which are suggestive of phthalocyanine-centered first oxidation and reduction processes. Photophysics of 3 and 4 were investigated by steady-state fluorescence and time-resolved transient absorption spectroscopy demonstrating the influence of the carbazole substituents on deactivation from the first excited state in 3 and 4. Protonation of the meso-nitrogen atoms in 3 results in much faster deactivation kinetics from the first excited state. Spectroscopic data were correlated with density functional theory (DFT) and time-dependent DFT calculations on 3 and 4.

A series of stilbazolium salts with A-π-A model and their third-order nonlinear optical response in the near-IR region

A series of water-soluble stilbazolium salts with A-π-A (A: Acceptor) model have been synthesized and fully characterized. The results obtained from absorption spectra and TD-DFT computational studies show that there is a relative strong intramolecular charge transfer (ICT) transition from pyridine unit to pyridine cation of the stilbazolium salts. Furthermore, it is found that the three stilbazolium salts (T1, T2, T3) show the strong two-photon absorption (2PA) response in the near-infrared (IR) region by Z-scan technique using femtosecond laser. And the stilbazolium salt T3 shows the largest two-photon absorption cross-section and third-order nonlinear optical (NLO) coefficient χ⁽³⁾ at 730nm, indicating the different terminal substituent group of the pyridinium plays a vital role in third-order NLO behavior.