Liquid-Exfoliated 2D Materials for Optoelectronic Applications

Two-dimensional (2D) materials have attracted tremendous research attention in recent days due to their extraordinary and unique properties upon exfoliation from the bulk form, which are useful for many applications such as electronics, optoelectronics, catalysis, etc. Liquid exfoliation method of 2D materials offers a facile and low-cost route to produce large quantities of mono- and few-layer 2D nanosheets in a commercially viable way. Optoelectronic devices such as photodetectors fabricated from percolating networks of liquid-exfoliated 2D materials offer advantages compared to conventional devices, including low cost, less complicated process, and higher flexibility, making them more suitable for the next generation wearable devices. This review summarizes the recent progress on metal-semiconductor-metal (MSM) photodetectors fabricated from percolating network of 2D nanosheets obtained from liquid exfoliation methods. In addition, hybrids and mixtures with other photosensitive materials, such as quantum dots, nanowires, nanorods, etc. are also discussed. First, the various methods of liquid exfoliation of 2D materials, size selection methods, and photodetection mechanisms that are responsible for light detection in networks of 2D nanosheets are briefly reviewed. At the end, some potential strategies to further improve the performance the devices are proposed.

Synthesis and investigation of the electrical properties of novel liquid-crystal phthalocyanines bearing triple branched alkylthia chains

The synthesis and electrical characterization of liquid crystalline and conducting properties of novel peripheral- and non-peripheral-tetra 2-(tri(hexylthio))ethoxy- and 2-(tri(octylthio))ethoxy-substituted copper(ii) phthalocyanines have been reported.

Construction and Characterization of Phthalocyanine-Loaded Particles of Curdlan and Their Photosensitivity

To optimize the physicochemical properties of phthalocyanine (PC), we examined its behavior in particles of triple helix glucan curdlan (CUR). CUR was denatured and renatured in DMSO, in the presence of PC. Infrared spectroscopy and transmission electron microscopy (TEM) showed that PC and CUR formed an inclusion complex, in which PC was trapped inside CUR molecules. This redshifted the absorption peak of PC, which would improve its usefulness as a photosensitizer, because infrared light can penetrate more deeply into human tissues. The conductivity of the solution of CUR-PC was higher than the conductivities of either a CUR solution or a PC dispersion, indicating that CUR-PC is more water soluble than PC. In addition, CUR-PC was highly stable in water. Thus, the use of CUR as a carrier of PC improves several of its physical properties. PC is used as a photosensitizer for killing cancer cells, but its use is hampered by its low solubility. Further, its absorption range limits its use to a depth of 1–3 mm in tissues. CUR-PC, with its high solubility and infrared absorption peak, was highly effective as a photosensitizer. It killed 84% of HeLa cells under 15 min of long wavelength radiation and had little cytotoxicity in the absence of light. These results demonstrate that CUR-PC has promise as a photosensitizer, as well as provide theoretical support for a wide range of applications for PC and CUR.

Novel phthalocyanines containing azo chromophores; synthesis, characterization, photophysical, and electrochemical properties

A series of novel metal-free and zinc (II), copper (II), cobalt (II), and manganese (III) phthalocyanine complexes bearing peripheral 2,6-dimethyl-4-(4-tert-butyl-phenylazo)phenoxy units have been synthesized. Novel phthalonitrile derivative required for the preparation of these phthalocyanine complexes was prepared by a base-catalyzed nucleophilic aromatic nitro displacement of 4-nitrophthalonitrile with 2,6-dimethyl-4-(4-tert-butyl-phenylazo)phenol. The structures of these new compounds were characterized by using elemental analyses, proton and carbon nuclear magnetic resonance, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy and mass spectrometry. The photophysical properties of metal-free and zinc(II) phthalocyanines were studied in tetrahydrofuran. The electrochemical properties of the phthalocyanine complexes were investigated by cyclic and square wave voltammetry.

Photophysical and photochemical properties of fluoroether-substituted zinc(II) and titanium(IV) phthalocyanines

The synthesis and characterization of novel zinc(II) (1a–4a) and oxo-titanium(IV) (1b–4b) phthalocyanine derivatives bearing 1H,1H-nona?uoro-3,6-dioxaheptan-1-ol groups are described for the first time. These phthalocyanines (1a–4a and 1b–4b) were characterized by elemental analysis and different spectroscopic techniques such as UV-vis, [Formula: see text]H NMR, FTIR and mass. Furthermore, the photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen generation and photodegradation) properties of these phthalocyanines were investigated in tetrahydrofuran (THF) solution. The influence of the number of the substituted groups (tetra or octa), position of the substituents (peripheral or non-peripheral) and central metal atom (zinc or titanium) on the photophysical and photochemical properties of these phthalocyanines were evaluated.

DBU-Catalysed Synthesis of Metal-Free Phthalocyanines and Metallophthalocyanines Containing 2(3,4-Dimethoxyphenyl)Ethanol and 4-Hydroxybenzaldehyde Groups: Characterisation, Antimicrobial Properties and Aggregation Behaviour

The synthesis, characterisation, and spectral and antimicrobial properties of novel peripherally tetra-substituted metal-free phthalocyanines and metallophthalocyanines bearing four 2(3,4-dimethoxyphenyl)ethanol or 4-hydroxybenzaldehyde substituents is reported. The aggregation behaviour of these compounds was investigated in different concentrations of DMSO. The compounds exhibited antimicrobial activity against test microorganisms.

Optimally tuned functionals improving the description of optical and electronic properties of the phthalocyanine molecule

By means of Density functional theory and time-dependent density functional theory calculations, we present a comprehensive investigation on the influence of different functional schemes on electronic and optical properties of the phthalocyanine molecule. By carrying out our own tuning on the OT-LC-BLYP/6-31G(d,p) functional, we show that such a procedure is fundamental to accurately match experimental results. We compare our results to several others available in the literature, including the B3LYP/6-31+G(d,p) set, which is commonly portrayed as the best combination in order to obtain a good description of the band gap. The results obtained here present not only significant improvement of the optical properties from the conventional BLYP, but we can also objectively report an improvement of our tuned functional when compared to the current benchmark of the literature as far as optical properties are concerned. Particularly, by means of this approach, it was possible to achieve a good agreement between the theoretical and experimental optical gap as well as of the positioning of the main peaks in the absorption spectrum. Our results thus suggest that correcting the long-range term on exchange term of the Coulomb operator, by means of a tuning procedure, is a good option to accurately describe properties of the phthalocyanine molecule.

The effects of substituent position on kinetics of benzene vapour adsorption onto 3-phenylphenoxy substituted metal-free and metallo-phthalocyanines thin films

The preparation of metal-free, Zn(ii), In(iii), and Cu(ii)-phthalocyanines containing tetrakis-(3-phenylphenoxy) groups was achieved.

Stable nano-sized copper and its oxide particles using cobalt tetraamino phthalocyanine as a stabilizer; application to electrochemical activity

CVs showing the electrocatalytic reduction of dioxygen with (a) bare GC; GC modified with (b) CoPTA; (c) metallic oxide nanoparticles after exposing the particles to air for 1 day and (d) CoPTA capped copper nanoparticles.

Synthesis and characterization of novel tetrakis (3-hydroxypropylmercapto)-substituted phthalocyanines

A phthalonitrile precursor 4-(3-hydroxypropylmercapto)phthalonitrile (3) was synthesized via a base-catalyzed nucleophilic aromatic nitro displacement of 4-nitrophthalonitrile with the 3-mercapto-1-propanol. A novel tetrasubstituted metal-free phthalocyanine (4) ( M = 2 H ) and its metal complexes (5–8) ( M = Zn , Ni , Cu and Co ) bearing 3-hydroxypropylmercapto moieties were prepared by the cyclotetramerization reaction of (3) with the appropriate materials. The visible spectra of the zinc(II) phthalocyanine (5) was recorded with different concentrations and different ions as Ag +, Hg 2+ and Pb 2+ in DMF and also with different solvents as dimethylformamide and pyridine. Fluorescence spectrum of the compound (5) was also studied. Temperature and frequency dependence of AC conductivity for (4–8) was investigated in air and under vacuum and were found to be ~10-8–10-5 S.m-1. Thermal properties of the phthalocyanines were examined by differential scanning calorimetry. All the novel compounds have been characterized by elemental analysis, UV-vis, FT-IR, NMR and MS spectral data and DSC techniques.

Magnetism and multiplets in metal-phthalocyanine molecules

Magnetism and multiplets for metal-phthalocyanine (MPc) molecules with transition-metals (M) of Mn and Co were investigated based on the constraint density functional theory calculations by imposing density matrix constraint on the d-orbital occupation numbers. For the MnPc, the ground state is found to be the 4Eg state with the perpendicular magnetic anisotropy with respect to the molecular plane, while for the CoPc, the ground state is the 2A1g state with a planar magnetic anisotropy.

Synthesis and Characterisation of New Metallophthalocyanines Containing Four 12-Membered Diazadithia-Macrocyclic Moieties

Tetrasubstituted zinc, cobalt, nickel, copper and lead phthalocyanines bearing four 12-membered diazadithia macrocyclic moieties on peripheral positions have been synthesised by cyclotetramerisation reaction of 1,10-ditosyl-1,2,3,5,6,8,9,10-octahydrobenzo[h][1,4,7,10]dithiadiazacyclododecine-12,13-dicarbonitrile and corresponding anhydrous metal salts under microwave irradiation. The thermal stabilities of the phthalocyanine compounds have determined by thermogravimetric analysis.

Electrochemical properties of octakis(hydroxyethylthio)-substituted phthalocyanines

Cyclic voltammetry of octakis(hydroxyethylthio)-substituted phthalocyanines with 2 H ( H 2 OHETPc ), Zn (II) ( Zn II OHETPc (−2)) and Co (II) ( Co II( OHETPc (−2)) in the phthalocyanine core has been investigated in dimethylsulfoxide ( DMSO ), and some of the results were evaluated together with their absorption spectra in the visible range. The redox processes due to both aggregated and non-aggregated species were observed on the voltammograms of phthalocyanines with Zn (II). The effect of chloride ion on the cyclic voltammetry of Co II OHETPc (−2) has been investigated in the DMSO / ClO 4− couple. The comparison of cyclic voltammetry for Co II OHETPc in the absence and presence of chloride ion showed that chloride ion does not bind to either Co (II) or Co (I) but does bind very strongly to Co (III). The detailed electrochemistry of Co II OHETPc (−2) was investigated in terms of the Co (I)/ Co (II) and Co (II)/ Co (III) redox couples, and various equilibria related to the species coordinated to Co (II) and Co (III) in the phthalocyanine core.

Electrochemical and Adsorption Properties of Novel Phthalocyanines with Four 16-Membered Diazadithia Macrocycles

Cyclic voltammetric measurements of Cu (II) and Ni (II) phthalocyanines with four 16-membered diazadithia macrocycles (1 and 2) and pentanuclear Ni (II) phthalocyanine bearing four Cu (II) ions in diazadithia macrocycles at the peripheral positions (3) have been carried out on platinum in DMSO and in aqueous medium 3 showed strong adsorption properties in DMSO and especially in aqueous medium, possibly as a result of the interaction between the copper ions in the four macrocycles and the platinum working electrode. Interestingly, the oxidation peak of 3 was split into two waves in aqueous medium. This behaviour is discussed in terms of disaggregation of the mixed valence species produced by the oxidation of aggregated species. A mechanism for both the oxidation of the complex and the splitting of the oxidation peak into two waves is suggested.

UV-vis and Binding Studies of Cobalt Tetrasulfophthalocyanine–Thiolate Complexes as Intermediates of the Merox Process

Intermediates of the cobalt tetrasulfophthalocyanine ( CoTSPc )-catalyzed thiol autoxidation were studied by UV-vis spectroscopy. All thiolates react with CoTSPc resulting in the formation of 1:1 complexes. Three major factors control both the stability and aggregation of the complexes: thiolate basicity, metal-to-ligand charge transfer (MLCT) and π stacking. Basic thiolates partially reduce C oII TSPc , whereas CoTSPc complexes with low-basicity aliphatic thiolates ( p K a < 4) do not exhibit Co (II) reduction, based on the absence of the characteristic Co (I) charge transfer band at 450 nm. CoTSPc complexes with aliphatic and bulky aromatic thiolates appear to be aggregated in aqueous solutions and are characterized by a broad band at 650 nm. Non-bulky aromatic thiolates of low basicity ( p K a < 6) form unique stable monomeric Co II TSPc complexes. This unique spectral feature can be attributed to π stacking between the phthalocyanine ring and thiolate. Comparison of binding constants shows that the partial reduction of Co (II) significantly contributes to the thiolate binding. A combination of aromatic π stacking and MLCT appears to be responsible for the observed 1000-fold stronger binding of non-basic aromatic thiolates as compared with aliphatic ligands of similar basicity. Kinetic studies confirm the importance of the thiolate binding type for catalysis.

New phthalocyanines containing bulky electron rich substituents

Metal-free and metallophthalocyanines with four 9-anthroyl groups bound through ethylthio ester bridges on the periphery have been prepared. The new compounds were characterized by elemental analyses, 1 H NMR, IR, mass and UV-vis spectral data. The electronic spectra exhibit an intense π-π* transition of 9-anthroyl identity together with characteristic Q and B bands of the phthalocyanine core. Effect of metal ions on intensity of fluorescence spectra of phthalocyanine derivatives substituted with 9-anthroyl groups was investigated. The energy transfer to the phthalocyanine core and radiative decays of the 9-anthroyl emission and phthalocyanine core were examined.

Synthesis and photophysical properties of zinc phthalocyanines substituted with quinolinoxy group

The synthesis of tetrasubstituted zinc phthalocyanines bearing quinolinoxy groups are reported for the first time. The new compounds have been characterized by elemental analysis, IR, MS and electronic spectroscopy. The photophysical properties, such as the electronic absorption spectra and fluorescence spectra, have also been investigated and discussed together with the influence of substituent position and organic solvents on these properties. The introduction of quinolinoxy group to the Pc ring was found to affect these photophysical properties to some extent.

Spectrophotometric and electrochemical studies of the interaction between iron(II) tetrasulfophthalocyanine and histamine

The interaction between iron(II) tetrasulfophthalocyanine ([ Fe II TSPc ]4+) and histamine results in the oxidation of the central metal by oxygen in the former, with the formation of a complex denoted as [(His) Fe III TSPc ]3− (where His = histamine). The rate constant for the formation of the complex is kf = 2.41 × 10−2 dm 3.mol−1.s−1 and an equilibrium constant of 6.3 dm3.mol-1 was obtained. The oxidation state of the central metal of [ Fe II TSPc ]4− before and after the coordination of histamine is confirmed by spectroelectrochemistry. Further electrochemical oxidation of this [( His ) Fe III TsPc ]3− derivative results in a metal-based process proposed to involve an Fe IV phthalocyanine species.

A convenient synthesis of phthalocyanines bearing four methyl 4-hexyloxyphenyl-2-phenoxy acrylate functionalities

A novel synthetic pathway for the preparation of a new phthalonitrile derivative, methyl (E)-3-[2-(3,4-dicyanophenoxy)-4-(hexyloxy)phenyl]acrylate (3), based on the opening of the lactone ring of 7-hexyloxycoumarin (2H-1-benzopyrane-2-one, 2H-chromen-2-one) and ether formation of the formed hydroxy group with 4-nitrophthalonitrile, is presented. Cyclotetramerization of this dinitrile in 2-N,N-dimethylaminoethanol gives the desired Zn(II) , Co(II) and Cu(II) phthalocyanines (4, 5 and 6) with four methyl 4-hexyloxy-2-phenoxy acrylate moiety on periphery. The complexes are characterized by IR, elemental analysis, 1 H NMR, 13 C NMR MALDI-TOF and UV-vis spectroscopy. The redox behavior of the complexes are also discussed.

A career in phthalocyanine chemistry – the Linstead Award 2002

A stroll through memory lane highlighting the author's contributions to phthalocyanines, including synthetic aspects especially of binuclear species, manganese oxygen breathing chemistry, mixed valence species, solution and surface electrochemistry, electrocatalysis, two-electron concerted processes, charge transfer spectroscopy, ligand electrochemical parameter applications and phthalocyanine design.

Microwave assisted synthesis of substituted metallophthalocyanines and their catalytic activity in epoxidation reaction

Substituted iron and cobalt phthalocyanines are easily prepared by microwave irradiation of the starting materials under solvent free condition, which reduced reaction time considerably. The synthesized metallophthalocyanines (octachloro-, tetranitro-, tetracarboxy- or polyphthalocyanine) are used as epoxidation catalysts of cyclooctene in homogeneous and heterogeneous conditions by iodosylbenzene as an oxidant. Their catalytic activities have shown that the electron withdrawing groups on the phthalocyanine ring have a very small effect on stability of the catalyst during the reactions.

Synthesis and characterization of a new (phthalocyani-nato)bis(carboxylate) silicon(IV) compound with increased solubility

The synthesis and spectroscopic characterization of a new soluble silicon(IV) phthalocyanine complex is presented. The compound shows an increased solubility compared to its SiPcCl 2 precursor and this allowed solution 1 H NMR characterization. The assignment of the 1 H NMR signals for the axial ligands is greatly facilitated due to the anisotropic high ring current effects from the macrocycle. In addition, good quality crystals were grown from this more soluble material for molecular structure determination by single-crystal X-ray diffraction analysis. The molecular structure determination shows that the complex crystallizes in a non-centrosymmetric space group due to the inherent chirality of the naproxene ligands. Bond lengths and angles fit well to other analogous compounds previously reported.