Ring-based Redox Processes Research Articles

Electrochemical and In-situ exhibited spectroelectrochemical properties of novel 4,4′-(3,5-di-tert-butyl-1,2-phenylene)bis(oxy) substituted ball-type phthalocyanine compounds

In this study, binuclear ball-type metallophthalocyanine compounds Co2Pc2(2), Fe2(OAc)2Pc2(3), Mn2(OAc)2Pc2(4), Ni2Pc2(5), Zn2Pc2(6) were obtained by using 4,4′-((3,5-di-tert-butyl-1,2-phenylene)bis(oxy))diphthalonitrile, and metal salts (mol ratio of metal salts and ligand:5/1), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst in 0.25 mL dimethylethanolamine at reflux temperature for about 20 min. Phthalocyanines have shown high solubility in common organic solvents since they contain eight bulky butyl groups and showed minimal aggregation in common solvents. The chemical structure of the complexes and their precursor has been characterized by spectral methods and elemental analysis. Electron transfer properties of all ball-type metallophthalocyanines were studied by using electrochemical and in-situ spectroelectrochemical measurements in non-aqueous media. Two kinds of electron transfer processes, i.e., metal-based and phthalocyanine ring-based redox processes, were revealed by these complexes. The electrochemical experiments displayed the establishment of discrete mixed-valenced oxidized as well as reduced groups resulting from intramolecular interactions between the two phthalocyanines and two metal units in novel ball-type complexes. Advanced redox properties of these complexes developed noticeable spectral and color changes, detected by in-situ spectroelectrochemical measurements in a solution medium.

Spectroscopic, electrochemical and optical properties of non-peripherally (2,2-dimethyl-1,3-dioxolan-4-yl)methoxy groups substituted metal-free and metallophthalocyanines

Metal-free and metallophthalocyanine complexes (M = 2H, InCl, or MnCl) containing (2,2-dimethyl-1,3-dioxolan-4-yl)methoxy groups were synthesized and characterized. The electrochemical properties of the phthalocyanine complexes were investigated by cyclic and square wave voltammetry. Metal-free and indium phthalocyanines give ring-based oxidation and reduction processes, while manganese phthalocyanine gives both metal and ring-based redox processes. Thin films of phthalocyanines were prepared by spin coating technique. The films were investigated as a function of the different metal ions in the inner core, with the transmittance spectrum measured at a wavelength range of 200–1000 nm. The results show that type of metal ions in the phthalocyanine core clearly change the transmittance values of the thin films of phthalocyanine complexes. Surface morphologies of the films were characterized by scanning electron microscopy. It has been observed that metal-free films form a more continuous and non-porous structure, while InPc and MnPc films have a porous surface.

Synthesis, characterization and electrochemical studies of metal-free and metallophthalocyanines containing two different chalcone units substituted on peripherally positions

In this paper, novel two different chalcone compounds (E)-3-(5-chloro-2-hydroxyphenyl)-1-o-tolylprop-2-en-1-one (2a) and (E)-3-(5-bromo-2-hydroxyphenyl)-1-(2-methoxyphenyl)prop-2-en-1-one (2b) and their phthalonitrile compounds (3a and 3b) were synthesized in the first step. Then, metal-free (4a and 4b), cobalt (II) (5a and 5b), copper (II) (6a and 6b) and manganese (III) (7a and 7b) phthalocyanines containing chalcone groups at peripheral positions were synthesized. All novel compounds were characterized by general spectroscopic techniques. The electrochemical studies of cobalt (II) (5a and 5b), copper (II) (6a and 6b) and manganese (III) (7a and 7b) phthalocyanine complexes were determined by cyclic voltammetry (CV) and square-wave voltammetry (SWV). Electrochemical studies display that while the CuPc (6a and 6b) shows just Pc ring-based redox processes, the CoPc (5a and 5b), MnClPc (7a and 7b) exhibit both metal-based and ring based redox reaction owing to the metal 3d orbitals lying among the Pc HOMO and LUMO.

Synthesis, characterization, and electrochemical and in-situ spectroelectrochemical properties of novel peripherally and non-peripherally 7-oxy-3-(3,4-dimethoxyphenyl) coumarin substituted phthalocyanines

Novel metal-free (4 and 9), Zn(II) (5 and 10) and Co(II) (6 and 11) phthalocyanines (Pcs) bearing four 7-oxy-3-(3,4-dimethoxyphenyl)coumarin (1) substituents at peripheral (β) and non-peripheral (α) positions have been prepared by cyclotetramerization reactions of 4-(3-(3,4-dimethoxyphenyl)coumarin-7-oxy)phthalonitrile (3) or 3-(3-(3,4-dimethoxy-phenyl)coumarin-7-oxy)phthalonitrile (8), respectively, in the presence of relevant metal acetate salts in N,N-dimethylaminoethanol. The compounds have been characterized by elemental analysis, FT-IR, UV–Vis and MALDI-TOF mass spectroscopies. Thermal properties of the compounds were evaluated by thermogravimetric analysis and differential scanning calorimetry. Electrochemical redox properties of all compounds were investigated by voltammetric and in-situ spectroelectrochemical measurements in dimethylsulfoxide including tetrabutyl ammonium perchlorate as the supporting electrolyte. The metal-free and Zn(II)Pc compounds displayed Pc ring-based redox processes whereas both Pc ring-based and metal-based electron transfer processes were observed for Co(II)Pc complexes. H-aggregation tendency of peripherally substituted compounds was found to be much higher than that of non-peripherally substituted ones. It was observed that there have been systemmatic redox potential and aggregation behaviour differences between the peripherally and non-peripherally substituted Pc compounds. These differences were attributed to different sterical and conformational effects of these substitution patterns. In-situ spectroelectrochemical and in-situ electrocolorimetric measurements suggested that peripherally substituted Co(II)Pc is a multi-coloured chromophore material displaying distinct spectral and colour changes during the first reduction and oxidation processes, and thus, being suitable for electrochromic applications.

High Electrochemical Versatility and Applicability with Metal Phthalocyanines Carrying Peripheral 2,3-dihydro-1H-inden-5-yloxy Substituents: Rich Redox Behavior, Oxygen Electrocatalysis and Electrochromism

The presence of cobalt(II), iron(III) and manganese(III) in the peripherally 2,3-dihydro-1H-inden-5-yloxy substituted phthalocyanine (Pc) core enriched their redox character in non-aqueous media with additional reversible metal-based reduction and oxidation couples, compared to their metal-free and tin(IV) Pc analogues displaying only Pc ring-based redox processes. The existence of trace amount of dioxygen in the electrolyte system was observed to considerably influence the redox behaviors of FePc and MnPc. As a result of the enhanced interaction between dioxygen and the central metal, the FePc showed much higher catalytic performance for oxygen reduction reaction than those of the others. It was also nearly insensitive to the presence of methanol. The comparison with the Pt-based catalyst showed that it could be a good alternative to the platinum as cathode catalyst, especially in direct methanol fuel cells. Furthermore, the association of the redox processes of metal Pcs with distinct spectral and color changes pointed out the possibility of their application as electrochromic materials. Langmuir Blodgett film of Mn(Cl)Pc compound on the indium tin oxide glass behaved as ideal neutral and cathodic coloring material, displaying red to green and red to purple color changes between its cationic forms with fast response time and high optical stability.

Comparative studies of photophysical and electrochemical properties of sulfur-containing substituted metal-free and metallophthalocyanines

The synthesis, photophysical and electrochemical properties of soluble sulfur-containing 4-(methylthio) benzenethiol substituted, non-peripherally metal-free and metallo (Zn, Ga, Co, and Mn) phthalocyanine complexes (2–6) are reported for the first time. The new phthalocyanines have been characterized by FT-IR spectroscopy, 1H-NMR, 13C-NMR, mass and UV–Vis spectroscopy techniques. Spectroscopic properties of these compounds were investigated in different solvents. Spectral and photophysical (fluorescence quantum yield) properties of metal free (2), zinc(II) (3), and gallium(III) phthalocyanines (4) were reported in different solvents toluene, tetrahydrofuran, and dimethyl sulfoxide. These results suggest that the solvents play role on the fluorescence quantum yields Φ F of the synthesized complexes (2–4). The electrochemical studies exhibit that while complexes (3) and (4) give only Pc ring-based redox processes, complexes (5) and (6) give both metal and ring-based redox reactions due to the energy level of metal in the Pc core lie between the HOMO and the LUMO of the ring.

Non-aggregated axially naphthoxazin group substituted silicon phthalocyanines: Synthesis and electrochemistry

In this study, the new 2-[2-(1H-naphtho[1,2-e][1,3]oxazin-2(3H)-yl)ethoxy]ethanol, 6-(1H-naphtho[1,2-e][1,3]oxazin-2(3H)-yl)hexan-1-ol have been synthesized. Then, novel axially naphthoxazin substituted two silicon(IV) phthalocyanines (SiPcs) have been synthesized and characterized. The aggregation behavior of SiPcs were examined in different solvents and concentrations in DMSO. In all studied solvents and concentrations, SiPcs were non-aggregated. The reduction and oxidation behavior of the axially disubstituted SiPcs were established by cyclic (CV) and square wave (SWV) voltammetry. Axially naphthoxazin substituted silicon(IV) phthalocyanines were observed to display phthalocyanine ring-based redox processes.

Highly soluble tetra lauryl alcohol substituted phthalocyanines; synthesis, electrochemistry, spectroelectrochemistry

The tetra peripherally β-substituted 2(3),9(10),16(17),23(24)-tetrakis undecyloxy phthalocyanine derivatives, M{Pc[O-(CH2)11CH3)]4} Pc: Phthalocyanine, [M: Zn(II)(2), Ga(III)(3), and Ti(IV)(4)], have been synthesized and characterized using FT-IR, 1H, and 13CNMR, MS (MALDI-TOF), UV–vis, atomic force microscopy, electro and spectroelectro chemical and elemental analysis. The new synthesized complexes are soluble in both polar solvents and nonpolar solvents, such as THF, DMF, CHCl3, CH2Cl2, benzene, and even hexane. Electrochemical and spectroelectrochemical measurements give common metal-based and/or Pc ring-based redox processes which support the proposed structures of the complexes. While titanium phthalocyanine exhibits metal- and Pc ring-based reduction and/or oxidation couples, gallium and zinc phthalocyanines give only Pc ring-based electron transfer processes.

Synthesis, characterization and comparative electrochemistry of beta and alpha tetra-[4-oxy-3-methoxybenzoic acid]-substituted Zn(II), Co(II) and Cu(II) phthalocyanines

In this study, novel beta and alpha tetra-[4-oxy-3-methoxybenzoic acid]-substituted Co(II), Zn(II) and Cu(II) phthalocyanines were prepared by the cyclotetramerization of the new phthalonitriles (1)/(2) and the corresponding divalent metal salts. The compounds were characterized by spectral data (IR, UV–Vis, 1H NMR and mass spectroscopies) as well as elemental analysis. These metallophthalocyanines showed excellent solubility in most organic solvents. The reduction and oxidation behaviour of the alpha- and beta-substituted complexes were established by voltammetry and in situ spectroelectrochemistry. The complexes were observed to display metal- and/or phthalocyanine ring-based redox processes. The redox and aggregation behaviours of the phthalocyanine complexes were found to be affected considerably by the nature of the substitution.

Electrochemical Evidence of Intramolecular Electronic Communication in Zr and Hf Phthalocyanines Bearing Ferrocene-Containing β-Diketonato Axial Ligands: Structure of [PcHf(FcCOCHCOC6H5)2

The series of zirconium(IV) and hafnium(IV) phthalocyanine complexes [PcM(FcCOCHCOR)2] (Pc = phthalocyaninato; M = Zr; R = CF3 (1), CH3 (2), C6H5 (3), Fc ((C5H5)Fe(C5H4), 4), as well as M = Hf ; R = CF3 (5), CH3 (6), C6H5 (7), and Fc (8)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf(FcCOCHCOC6H5)2], 7 (Z = 2, space group P1), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of 7 it was clear that these complexes have a distorted D4h symmetry at the coordination site of the metal centers, which explains a splitting of the UV-vis Q band into Qx and Qy components with 3 ≤ Δλ(max,Q) ≤ 10 nm. Cyclic and square wave voltammetric studies in CH2Cl2/[N((n)Bu)4][B(C6F5)4] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in 1-8. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be E°' = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV-vis Q-band maximum wavelengths, and HOMO-LUMO energy gaps as expressed by ΔE°'I-III = ΔE°'wave I - ΔE°'wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, ΣχR. Mathematical relationships for the dependency of E°' on ΣχR for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands.

Crown ether-substituted water soluble phthalocyanines and their aggregation, electrochemical studies

The synthesis of a new metal-free, zinc (II), cobalt phthalocyanines and their water soluble quaternized derivatives 5a, 6a substituted with four crown ether groups are described. The aggregation behavior of these compounds was investigated in different concentrations of DMSO. The effect of solvents on absorption spectra was studied in various organic solvents. Water soluble phthalocyanines 5a and 6a were investigated for their aggregation behavior in DMSO, DMF, water and in various DMSO/water mixtures by comparing their UV–Vis spectra. Water soluble phthalocyanines in DMSO and in up to 50 vol.% DMSO/water are nonaggregated. But increasing amounts of water leads to higher aggregation ratios. Electrochemical properties of phthalocyanines were investigated by cyclic and square wave voltammetry. While cobalt phthalocyanine displayed metal and ring-based redox processes, the other phthalocyanines displayed only ring-based redox processes.

Oxygen reduction reaction catalyzed with titanyl phthalocyanines in nonaqueous and aqueous media

Electrochemical and in situ spectroelectrochemical behaviors and electrocatalytic reduction of molecular oxygen with titanyl phthalocyanines (TiPc) bearing 3,4-(methylenedioxy)-phenoxy substituents were performed in aprotic solvents. Multi electrons and metal-based and ring-based redox processes of TiPcs indicate their possible electrocatalytic activity toward many target species. Different numbers and positions of the substituents of the complexes affect the peaks' character and assignment of the processes. The presence of O2 in the electrolyte system influences the electrochemical and spectral responses of TiPcs. Electrochemical and in situ spectroelectrochemical analysis indicates interaction of molecular oxygen with TiPcs and these interaction mechanisms depend on both the substituent environments of the complexes and the electrolyte system. Langmuir-Blodgett films of the complexes also catalyze molecular oxygen in aqueous media, which is a desired property for their practical application.

Synthesis and electrochemical investigation of phthalocyanines with dendritic bulky ethereal substituents

Metal-free and metallophthalocyanines carrying four dendritic 3,4-bis(benzyloxy)benzyloxy groups on the periphery were prepared by cyclotetramerization of a new precursor, namely 4-[3,4-bis(benzyloxy)benzyloxy]phthalonitrile (2) in the presence of the corresponding divalent metal salts (Zn(II), Co(II)). The novel phthalonitrile derivative 2 was synthesized by the reaction of 4-nitrophthalonitrile and 3,4-dibenzyloxybenzyl alcohol (1), which was prepared by the catalytic reduction of 3,4-dibenzyloxybenzaldehyde with NaBH4 in ethanol. The new compounds were characterized by elemental analysis, together with FT-IR, 1H NMR and UV–Vis spectra. The electrochemical and in situ spectroelectrochemical measurements showed that while the cobalt phthalocyanine complex (5) gives both metal-based and ring-based redox processes, the metal-free and zinc phthalocyanine complexes (3 and 4) give only ring-based electron transfer processes. An in situ electrocolorimetric method was applied to investigate the colour of the electrogenerated anionic and cationic forms of the novel phthalocyanine complexes carrying bulky ethereal aryloxy substituents.

Synthesis, photophysical, photochemical and electrochemical properties of crown ether bearing coumarin substituted phthalocyanines

Zinc (II), cobalt (II) and copper (II) phthalocyanines substituted at the peripheral (complexes 5, 6 and 7) and non-peripheral (complexes 8, 9 and 10) positions with 7,8-(15-crown-5)-3-(4-oxyphenyl)coumarin groups have been prepared and characterized. The photophysical and photochemical properties of zinc (II) Pc complexes (5 and 8) were also described. The singlet oxygen quantum yields (0.54 for 5, 0.65 for 8) are indicating the potential of the complexes as photosensitizers in applications of PDT. The redox processes of the complexes were identified by voltammetry and in situ spectroelectrochemistry. Alpha and beta-substituted complexes displayed metal- and/or phthalocyanine ring-based redox processes. It was found that the kind of substitution affects the redox processes of the phthalocyanine complexes considerably, due to the difference in their aggregation behaviors.

Synthesis and spectroelectrochemistry of new phthalocyanines with ester functionalities

Metal-free (H 2Pc) and metallophthalocyanines (MPc; M: Co, Zn) with four n-pentyl ester of thioglycolic acid groups have been synthesized by the esterification of the corresponding carboxylic acid derivatives with n-pentanol. The novel phthalocyanine compounds were characterized by elemental analyses, mass, FT-IR and UV–Vis spectral data. The aggregation investigations carried out in different concentrations and solvents indicate that ester substituted metal-free and metallo-phthalocyanine compounds have not shown any aggregation behavior in the concentration range of about 10 −5 M. Electrochemical and in-situ spectroelectrochemical measurements give common MPc based redox behaviors which supported the proposed structure of the complexes. While CoPc gives both metal-based and ring-based redox processes, H 2Pc and ZnPc give only ring-based electron transfer processes. In-situ electrocolorimetric method was applied to investigate the color of the electro-generated anionic and cationic forms of the complexes.

3,4-Ethylenedioxythiophene substituted phthalocyanines

Zinc and cobalt phthalocyanines, peripherally functionalized with electroactive and electropolymerizable groups were synthesized and their electrochemical, spectroelectrochemical, and electrocolorimetric properties were studied. While cobalt phthalocyanine gives both metal-based and ring-based redox processes, zinc phthalocyanine shows only ring-based electron transfer processes. Any redox signal belonging to thiophene groups is recorded within the potential window of the electrolyte system. However, when the complexes are over-oxidized with more positive switching potential, electropolymerization of the complexes on the working electrode are recorded. Presence of the EDOT groups differentiates the colors of the electrogenerated anionic and cationic forms of the complexes which indicate possible electrochromic applications of the complexes.

Electrocatalytic oxygen reduction and hydrogen evolution reactions on phthalocyanine modified electrodes: Electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric monitoring

This study describes electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric monitoring of the electrocatalytic reduction of molecular oxygen and hydronium ion on the phthalocyanine-modified electrodes. For this purpose, electrochemical and in situ spectroelectrochemical characterizations of the metallophthalocyanines (MPc) bearing tetrakis-[4-((4′-trifluoromethyl)phenoxy)phenoxy] groups were performed. While CoPc gives both metal-based and ring-based redox processes, H 2Pc, ZnPc and CuPc show only ring-based electron transfer processes. In situ electrocolorimetric method was applied to investigate the color of the electrogenerated anionic and cationic forms of the complexes. The presence of O 2 in the electrolyte system influences both oxygen reduction reaction and the electrochemical and spectral behaviors of the complexes, which indicate electrocatalytic activity of the complexes for the oxygen reduction reaction. Perchloric acid titrations monitored by voltammetry represent possible electrocatalytic activities of the complexes for hydrogen evolution reaction. CoPc and CuPc coated on a glassy carbon electrode decrease the overpotential of the working electrode for H + reduction. The nature of the metal center changes the electrocatalytic activities for hydrogen evolution reaction in aqueous solution. Although CuPc has an inactive metal center, its electrocatalytic activity is recorded more than CoPc for H + reduction in aqueous solution.

Synthesis and electrochemical, electrical and gas sensing properties of novel mononuclear metal-free, Zn(II), Ni(II), Co(II), Cu(II), Lu(III) and double-decker Lu(III) phthalocyanines substituted with 2-(2H-1,2,3-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl) phenoxy

A new mono substituted phthalonitrile derivative 3 was prepared by a nucleophilic displacement reaction of 4-nitrophthalonitrile with 2-(2H-1,2,3-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol. Novel metallophthalocyanines 4–8 (M=Zn, Ni, Co, Cu, Lu, respectively), metal free 9 and double decker Lu(III) phthalocyanine 10 with four peripheral 2-(2H-1,2,3-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenoxy groups were synthesized by cyclotetramerisation of the phthalonitrile and characterized by elemental analyses, FTIR, 1H NMR, UV–vis and MALDI-TOF MS spectral data. Cyclic voltammetry, differential pulse voltammetry and in situ spectroelectrochemistry of the phthalocyanine compounds have been studied. This allowed us to identify and compare metal- and phthalocyanine ring-based redox processes of the complexes. Impedance spectroscopy (IS) and dc conductivity measurements were performed as a function of temperature (300–430K) and frequency (40–105Hz.). The sensing properties of the films for toluene were also investigated. The dc results showed an activated conductivity dependence on temperature for all films. While room temperature impedance spectra consist of a curved line, a transformation into a full semicircle with increasing temperature was observed. The analysis of ac conductivity data showed that the CBH model is the dominant conduction mechanism for the electron transport in the films. While exposure to toluene has no effect on the conductivity of the film of 8–10 completely reversible sensor response to toluene only were obtained for compounds 4–7. It was also observed that the operating temperature had a considerable effect on sensing characteristics of the films.

Synthesis and electrochemical behavior of novel peripherally and non-peripherally substituted ball-type cobalt phthalocyanine complexes

The syntheses of new ball-type Co(II) phthalocyanines containing 4,4′-(9 H-fluorene-9,9- diyl)diphenol substituents at non-peripheral (complex 6) and peripheral (complex 7) positions are presented. These complexes were characterized by UV–Vis, FT-IR, mass spectroscopy and electrochemical methods. Both complexes exhibit metal and ring based redox processes, typical of cobalt phthalocyanine complexes. For 6, the metal based reduction was observed at −0.46 V followed by a ring based reduction at −1.40 V. The metal oxidation for 6 was observed at +0.16 V and the ring based oxidation at +1.05 V. For 7, reductions are easier but the oxidations are more difficult. The metal based reduction for 7 was observed at −0.38 V followed by a ring based reduction at −1.03 V. The metal oxidation for 7 was observed at +0.20 V and the ring based oxidation at +1.35 V.

Synthesis, electrochemical, in situ spectroelectrochemical and in situ electrocolorimetric characterization of new metal-free and metallophthalocyanines substituted with 4-{2-[2-(1-naphthyloxy)ethoxy]ethoxy} groups

The synthesis of novel metal-free and metallophthalocyanines [Ni(II), Zn(II), Co(II), Cu(II)] were prepared by cyclotetramerization of a novel 4-{2-[2-(1-naphthyloxy)ethoxy]ethoxy}phthalonitrile and the corresponding metal salts (NiCl 2, Zn(CH 3COO) 2, CoCl 2 and CuCl 2). The structures of the target compounds were confirmed using elemental analysis, IR, 1H NMR, 13C NMR, UV–Vis and MS spectral data. Voltammetric and in situ spectroelectrochemical measurements show that while cobalt phthalocyanine complex gives both metal-based and ring-based redox processes, metal-free, and zinc phthalocyanines show only ring-based reduction and oxidation processes. All complexes decomposed and coated on the electrode as nonconductive film at positive potential window of the electrolyte. An in situ electrocolorimetric method has been applied to investigate color of the electro-generated anionic and cationic forms of the complexes.