Synthesis, spectral and electrochemical characterization of non-aggregating α-substituted...

Synthesis, spectral and electrochemical characterization of non-aggregating α-substituted vanadium(IV)-oxo phthalo-cyanines

Zhou Jianga, Zhongping Oub∏∏, Naisheng Chen*a∏, Jundong Wanga, Jinling Huanga, Jianguo Shaob∏∏ and Karl M. Kadish*b∏

a Institute of research on Functional Materials, Fuzhou University, Fuzhou 350002, China b Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA

Received 16 December 2004Accepted 28 February 2005

ABSTRACT: Two α-substituted vanadium-oxo phthalocyanines, [(OC6H3(t-Bu)2)4Pc]VO and [(OC8H17)4Pc]VO, where OC6H3(t-Bu)2 is 2,4-di-tert-butylphenoxy and OC8H17 is 2,2,4-tri-methyl-3-pentoxy, were synthesized and characterized by elemental analysis, mass spectrometry, UV-visible, IR, ESR spectroscopy and electrochemistry. Both complexes have good solubility and do not aggregate in polar or non-polar solvents. Three reductions and two oxidations can be observed in DMF containing 0.2 M TBAP. A HOMO-LUMO gap of ~1.4 V is seen for both complexes. The first two one-electron reductions and first oxidation are reversible diffusion controlled electrode processes under the given experimental conditions. The effects of solvent and phthalocyanine macrocycle substituents on the Q bands of the electronic absorption spectra are discussed. Copyright © 2005 Society of Porphyrins & Phthalocyanines.

KEYWORDS: synthesis, spectroscopy, electrochemistry, vanadium-oxo phthalocyanines.

INTRODUCTIONPhthalocyanines have been studied with respect

to their importance in applications as photosen-sitizers for photodynamic therapy (PDT), catalysts, molecular materials, chemical sensors, non-linear optical materials, dyes and pigments [1-3]. Generally, unsubstituted phthalocyanines have poor solubility and a high tendency of aggregation in organic solvents [4], thus greatly limiting their use for various appli-cations. Alkyl, alkoxyl groups or other substituents have often been added to the periphery of the phthalocyanine macrocycle for improving solubility. Tetra-substituted phthalocyanines normally consist of four constitutional isomers and generally show

higher solubility than the corresponding unsubstitued or octa-substitued complexes. On the other hand, α-substituted phthalocyanines have higher solubility than the β-substituted complexes [4].

It is known that vanadium-oxo phthalocyanines exhibit a smaller HOMO-LUMO gap and a longer wavelength Q band in the near IR region than the phthalocyanines with no axial ligands. The excellent optical and photoelectronic properties of vanadium-oxo phthalocyanines have lead to their promising applications in the areas of electrophotographic techniques [5], optical recording materials [6] as well as non-linear optical (NLO) [7] and gas sensing [8] techniques. However, only a few vanadium-oxo phthalocyanines have been synthesized and characterized to date [9-11]. In this paper, the synthesis and characterization of two novel α-position tetra-substituted vanadium-oxo phthalocyanines (Chart 1) are described. Both vanadium-oxo complexes, tetra- α-(2,4-di-tert-butylphenoxy)vanadium-oxo phthalo-

*Correspondence to: Naisheng Chen, email: nschen@fzu.edu.cn, fax: +86 591-87892632 and Karl M. Kadish, email: kkadish@uh.edu, fax: +1 713-743-2745

∏SPP full member or ∏∏ student member in good standing

Journal of Porphyrins and Phthalocyanines Published at http://www.u-bourgogne.fr/jpp/

J. Porphyrins Phthalocyanines 2005; 9: 352-360

Published on web 06/16/2005

α-SUBSTITUTED VANADIUM(IV)-OXO PHTHALOCYANINES 353

cyanine, [(OC6H3(t-Bu)2)4Pc]VO 1 and tetra-α-(2,2,4-tri-methyl-3-pentoxy)vanadium-oxo phthalocyanine, [(OC8H17)4Pc]VO 2, where OC6H3(t-Bu)2 is 2,4-di-tert-butylphenoxy and OC8H17 is 2,2,4-tri-methyl-3-pentoxy, have a high solubility and exist as monomers in polar and non-polar organic solvents. The physicochemical properties and redox behavior of the compounds were obtained by elemental analysis, UV-visible, IR, mass spectrometry and ESR spectroscopy as well as by electrochemical and spectroelectrochemical measurements.

EXPERIMENTAL

Chemicals

N,N-dimethylformamide (DMF) was obtained from Aldrich Co. and used as received for electrochemical measurements. Tetra-n-butylammonium perchlorate (TBAP) was purchased from Sigma Chemical or Fluka Chemika Co., recrystallized from ethyl alcohol, and dried under vacuum at 40 °C for at least one week prior to use.

3-(2,4-di-tert-butylphenoxy)phthalonitrile and 3-(2,2,4-tri-methyl-3-pentoxy)phthalonitrile were syn-thesized according to the basic method reported in the literature [12]. All other reagents were of analytical grade and used as received.

Synthesis of 1(4),8(11),15(18),22(25)-tetra-(2,4- di-tert-butylphenoxy)vanadium-oxo phthalocya-nine, [(OC6H3(t-Bu)2)4Pc]VO (1). A mixture of 3-(2,4-di-tert-butylphenoxy)phthalonitrile (1.33 g, 4 mmol), V2O5 (0.1 g, 1 mmol), urea (5.0 g)， NH4Cl (0.9 g) and ammonium molybdate (0.01 g) were milled to form a uniform powder which was heated and stirred at 150 °C for 0.5 h and then at 190 °C for 4 h. The product was extracted using toluene and purified on a silica gel column. After evaporation of toluene (eluent), the remained green powder was washed with methanol and then dried in a vacuum desiccator at 80 °C (yield 48%). Anal. calcd. for C88H96N8O5V, %: C, 75.67; H, 6.93; N, 8.02. Found: C, 75.69; H, 7.14; N, 7.82. MS (ESI): m/z 1397.1 [M+H]+, (100%). IR: ν, cm-1 2956, 2866, 1589, 1482, 1398, 1362, 1249, 1212, 1135, 1077, 1009, 984, 747, 648, 492.

Synthesis of 1(4),8(11),15(18),22(25)-tetra-(2, 2,4-tirmethyl-3-pentoxy)vanadium-oxo phthalo-cyanine, [(OC8H17)4Pc]VO (2). This compound was synthesized and purified by the method described above for complex 1 and 3-(2,2,4-tri-methyl-3-pentoxy)phthalonitrile was used instead of 3-(2,4-di-tert-butylphenoxy)phthalonitrile (yield 17%). Anal. calcd. for C64H80N8O5V, %: C, 70.37; H, 7.38; N, 10.26. Found: C, 69.00; H, 7.01; N, 9.57. MS (ESI): m/z 1092.4 [M+H]+, (100%). IR: ν, cm-1 2958, 2912, 2877, 1588, 1487, 1395, 1388, 1335, 1272, 1243,

1135, 1015, 928, 743.

Preparation of LB film

The LB film of complex 1 was prepared with a KSV Minitrough II (Finland). Deionized water (15 MΩcm-1) was used as subphase. A microscopic slide was used as the substrate which was successively pretreated by ultrasonic cleaning with hot deionized water (50 °C), iso-propanol and chloroform for 15 min and then dried under vacuum. The phthalocyanines were dissolved in toluene and the concentration of the solution was 1.0 × 10-4 M. Then, the solution (150 μl) was carefully added drop by drop to the surface of the subphase with a micro-syringe. The floating thin film of the phthalocyanines was formed when the solvent volatilized. When the surface pressure was stable, the film was subject to symmetric compression at a rate of 3 mm.min-1 until the surface pressure reached 20 μN.m-1. Deposition of the LB film was then carried out under this pressure with a vertical dipping rate of 5 mm.min-1.

Instrumentation

IR spectra were measured in KBr pellets at room temperature with a PE-983G FTIR spectrophotometer. UV-vis spectra were analyzed via a PE Lambda-800 UV-vis spectrophotometer. Elemental analyses were performed by ELEMENTAR VARIO EL III. Mass spectra were collected with a LCQ Deca XP MAX(ESI) mass spectrometer. HPLC analyses were performed on the Waters HPLC system with 1525 dinary HPLC pump and 2996 photodiode array detector. Analytical condition: C18 column of 3.55 mm (ID) x 100 mm (long), particle size 15 μm, column temperature at 30 °C. HPLC grade DMF from TEDIA was used as eluent with a flow rate of 1.0 ml.min-1. Electron spin resonance (ESR) spectra were obtained on an IBM model ESP 300 apparatus. The low temperature ESR measurements were carried out via a liquid-nitrogen finger dewar.

Cyclic voltammetry was carried out a t 298 K by using an EG&G Princeton Applied Research (PAR) 173 potentiostat/galvanostat. A homemade three-electrode cell was used for cyclic voltammetric measurements and consisted of a platinum button or glassy carbon working electrode, a platinum counter electrode and a homemade saturated calomel reference electrode (SCE). The SCE was separated from the bulk of the solution by a fritted glass bridge of low porosity which contained the solvent/supporting electrolyte mixture. Thin-layer UV-visible spectroelectrochemical experiments were performed with a home-built thin-layer cell which has a light transparent platinum net working electrode. Potentials were applied and monitored with an EG&G PAR Model 173 potentiostat. Time-resolved UV-visible

Z. JIANG ET AL.354

spectra were recorded with a Hewlett-Packard Model 8453 diode array spectrophotometer. High purity N2 from Trigas was used to deoxygenate the solution and kept over the solution during each electrochemical and spectroelectrochemical experiment.

RESULTS AND DISCUSSION

Synthesis

Unsubstituted phthalocyanines generally have very poor solubility in common organic solvents. For example, a saturated solution of (Pc)VO is only 10-6 M in CH2C12 [9]. Because of this, the traditional purification procedure for unsubstituted phthalocyanines involves either removing the non-phthalocyanine components by repeated washings with acid, alkali and various organic solvents or repeatedly dissolving and reprecipitating the compound in sulfuric acid solution. The sublimation method is good for the purification of unsubstituted phthalocyanines but not for all of the substituted ones [3]. In the current work, the introduction of hydro-phobic substituents greatly improved the solubility of the examined vanadium-oxo phthalocyanines. The reaction products could be extracted with toluene to remove most non-phthalocyanine components and then subjected to silica gel column chromatography for further purification.

The structures of the compounds were confirmed by IR spectroscopy. For example, in the case of compound 1, bands are seen at 2956 and 2866 cm-1 which are attributed to νC-H of the alkyl group. Bands at 1589 and 1482 cm-1 are due to the skeletonal vibrations of the macrocyclic ring. Split double bands at 1398 and 1362 cm-1 and an absorption at 1212 cm-1 confirm the presence of the tert-butyl groups. Absorptions at 1249 and 1077 cm-1 are attributed to νC-O-C of the ether bond. The 1009 cm-1 frequency for the ν(VO) stretch of 1 is consistent with a previously characterized band at 1007 cm-1 for octakis(hexylthio)-vanadylporphyrazine [13] and at 1011-1013 cm-1 for binuclear vanadylphthalocyanines [11]. However the 1009 cm-1 band of 1 is larger than the 987 cm-1 reported for the porphyrin (OEP)VO [14] (OEP = octaethylporphyrin). It is also larger than the 970 cm-1 for the corrole complex (Me8)Cor(H)VO [15] and the 975 cm-1 for the corrolazine [(TBP)8Cz(H)]VO [16], where (Me8)Cor = octamethylcorrole and (TBP)8Cz = octakis(para-tert-butyl-phenyl)corrolazine, respectively.

In the synthesis of phthalocyanines,

cyclotetramerization of the unsymmetrical precursor, i.e. 3- and 4-substituted phthalonitriles or other phthalyl derivatives, often results in mixtures of all four possible isomers, i.e. those with D2h, C4h, C2v and Cs symmetries (Chart 1). When neglecting electronic and steric effects, a statistical distribution at a 1:1:2:4 ratios for the mentioned above isomers is expected [17]. However, the steric and electronic effects of the substituents arising from 3-substituted phthalonitriles can strongly affect the formation and ratio of the four different isomers and this would lead to a non-statistical distribution of the isomers [17]. In this work, three HPLC peaks can be seen at retention times of 4.3, 5.3 and 6.7 min, indicating at least three different isomers exist for [(OC6H3(t-Bu)2)4Pc]VO 1. However, only one peak is observed by analytical HPLC of [(OC8H17)4Pc]VO 2. This result suggests that only one of these isomers is obtained for 2 under the given experimental conditions and indicates that the more bulky and rigid substituents on this compound have a stronger steric effect which may lead to a relatively low yield of 17% for complex 2 vs 48% for [(OC6H3(t-Bu)2)4Pc]VO 1.

Substituents at the more sterically crowed α-position may cause distortion of the molecule [18]. As seen from Chart 1, the D2h isomer should have

Chart 1.

the largest distortion among the isomers because the two bulky substituents are crowed in the same pocket of the two benzo rings. The extent of distortion for these isomers follows the order: D2h > Cs = C2v > C4h. Some tetra-substituted phthalocyanines have been separated with a developed HPLC phase. The order of retention time is D2h < C2v ≤ Cs < C4h [19]. In this work, a separation of the constitution isomers with a common C18 column is possible. It is presumed that the difference in retention times of these isomers should be due to the distortion and/or the magnified differences in dipole moments inducing by the distortions. The isomers of [(OC6H3(t-Bu)2)4Pc]VO 1 have the same eluting sequence with the ratio of the absorbance at 7:20:1 for C4h:(Cs+C2v):D2h. The result suggests that the formation of the C4h isomer is favorable while D2h is greatly hindered due to steric effects of the bulky substituents on the α-positions.

UV-visible spectrum in solution

The λmax of the major Q band is red-shifted with increasing polarity of the solvent. A maximum red-shift of 13 nm is seen for [(OC6H3(t-Bu)2)4Pc]VO 1 and 20 nm for [(OC8H17)4Pc]VO 2 (see Table 1), which might be caused by a strong dipole-dipole interaction between the polar solvent and/or the phthalocyanine molecules.

(F16Pc)VO shows different absorption spectra in polar and non-polar solvents [10]. In non-polar solvents such as benzene or 1,2-dichlorobenzene, the Q band appears at 709 nm. In polar solvents such as DMF or dichloromethane, the band position is at 640 nm. The ~70 nm blue-shift of the Q band upon going from a non-polar to a polar solvent has been attributed to dimerization/aggregation of the complex in the polar solvent [10, 20-23]. However, this is not the case for [(OC6H3(t-Bu)2)4Pc]VO 1 or [(OC8H17)4Pc]VO 2, both of which shows a characteristic monomeric spectrum in common organic solvents such as pyridine, DMF, CH2Cl2, cyclohexane, n-hexane or toluene. The Q band of

these complexes ranges from 724 to 747 nm and is listed in Table 1. The UV-visible spectra of 1 and 2 exhibit no significant blue-shift of the Q band when the solvent is changed from the polar DMF to the non-polar n-hexane (see examples for 1 in Fig. 1). This result indicates that aggregation does not occur for complexes 1 and 2 in either type of solvent, polar or non-polar. It can be considered that the bulkiness of the peripheral substituents on the phthalocyanine prevents aggregation [10].

The relationship between concentration and

Fig. 1. UV-visible spectra of compound 1 at different concentrations (A) in DMF at (a) 1.03, (b) 2.06, (c) 3.09, (d) 4.12, (e) 5.16, (f) 6.19 and (g) 7.22 × 10-6 M and (B) in n-hexane at (a) 0.50, (b) 1.00, (c) 2.00, (d) 3.00, (e) 4.00 and (f) 5.00 × 10-6 M

Table 1. UV-visible spectral data (the major Q band, λmax, nm) of compounds 1 and 2 and related phthalocyanines in different solvents

Compound n-hexane Cyclohexane Toluene CH2Cl2 CHCl3 DMF Py

[(OC6H3(t-Bu)2)4Pc]VO, 1 724 727 733 736 738 731 737

[(OC8H17)4Pc]VO, 2 727 730 739 742 742 744 747

(Pc)VO 694 696 688

[(t-Bu)4Pc]VO 700

(R4Pc)Cua 704 705 708 709 703 706

(R4Pc)Pda 686 689 690 692 692 694

a R is the α-substituent which is the same as that of compound 1; data taken from reference 12.

Z. JIANG ET AL.356

maximum Q band absorbance for complexes 1 and 2 obeys Beerʼs law both in DMF and n-hexane (see examples for 1 in Fig. 1). A linear relationship is seen from 5.0 × 10-7 to 7.2 × 10-6 M, further confirming that only monomeric species exist in these two solvents and that aggregation does not occur under the given experimental conditions.

It is known that the addition of electron-donating groups at the α-position of the phthalocyanines makes the HOMO-LUMO gap smaller and shifts the Q band, which is composed mainly of the HOMO-LUMO transition, to longer wavelengths [24]. The same is seen for [(OC6H3(t-Bu)2)4Pc]VO 1 and [(OC8H17)4Pc]VO 2. The electron-donating groups, aryloxy for 1 and alkoxy for 2, are bound to four α-positions of the complexes and lead to a Q band red-shift of 43 nm for 1 and 56 nm for 2, with respect to what is seen for unsubstituted (Pc)VO in DMF (see Table 1). Compared with complex 1, a larger red-shift of the Q band is seen for complex 2. This suggests that the alkoxy group of 2 is a stronger electron-donating group than the aryloxy group of 1, and the HOMO-LUMO gap of 2 should be smaller than that of 1. This is confirmed by the electrochemically measured HOMO-LUMO gaps of 1.38 V for 2 and 1.45 V for 1 (see Table 2).

Compared to the spectra of copper and palladium phthalocyanines which have no axial ligands but have identical substituents as 1, the Q band of the vanadium-oxo complexes 1 shows a significant red-shift in both polar and non-polar solvents (see Table 1). For example, the Q band is at 704 nm for the copper complex and at 686 nm for the palladium complex in cyclohexane. However, this band is red-shifted to 724 nm for compound 1 in the same solvent (Table 1). This result indicates that the energy of the π-π* transitions for V=O complex is much lower than that of Cu or Pd complexes.

UV-visible spectrum of LB film

Figure 2 shows the solution and LB film spectra of complex 1. For the LB film spectrum, one of the shoulder peaks has disappeared and a broad Q band is seen as compared to the solution spectrum. This result suggests that a stronger interaction may occur between molecules in the solid state than in solution. The red-shift of the Q bands for the LB film spectrum indicates that the molecules of 1 are arranged in an edge-to-edge form [2, 9]. It seems that the crowding from adjacent benzo groups and the presence of the axial oxygen atom of 1 would hinder the approach of the phthalocyanine molecules needed to arrange in a coplanar form or in the slipped form. The small value of the red-shift, i.e. 10 nm for the major Q band, can be attributed to a longer distance between the molecules and/or a larger distortion of the compound in the solid state.

Electrochemistry

The electrochemistry of [(OC6H3(t-Bu)2)4Pc]VO 1 and [(OC8H17)4Pc]VO 2 was carried out in DMF

Table 2. Half-wave potentials (V vs SCE) of vanadium(IV)-oxo complexes in DMF, 0.1 M TBAP

CompoundaOxidation Reduction ΔEred(1-2) HOMO-LUMO

Ref.2nd 1st 1st 2nd 3rd (V) gap (V)

[(OC6H3(t-Bu)2)4Pc]VO, 1 1.34b 0.94 -0.51 -0.97 -1.94b 0.46 1.45 tw

[(OC8H17)4Pc]VO, 2 1.21b 0.76 -0.62 -1.12 -2.07b 0.50 1.38 tw

[(Bu)4Pc]VO 0.94 -0.58 -1.08 0.50 1.52 9

(F16Pc)VOc 1.34 -0.29 -0.62 -1.41 0.33 1.63 10

[(TBP)8Cz(H)]VOc,d 1.01 -0.60b 1.61 16

(TPP)VO 1.32 1.01 -0.98 -1.50 0.52 1.99 25

[(Bu)4Pc]TiO 0.85 -0.52 -1.02 0.50 1.37 9

a (Bu)4Pc = tetra-tert-butylphthalocyanine; F16Pc = perfluorophthalocyanine; (TBP)8Cz = octakis(para-tert-butylphenyl)corro-lazine; TPP = tetraphenylporphyrin. b Ep, peak potential at a scan rate of 0.1 V/s. c In CH2Cl2. d Values converted from V vs Ag/AgCl to V vs SCE via E1/2(SCE) = E1/2(Ag/AgCl) + 0.045 V. tw: this work.

Fig. 2. UV-visible spectra of compound 1 in toluene (solid line) and in the solid state of a LB film (dashed line)

containing 0.1 M TBAP. The cyclic voltammograms of both compounds are shown in Fig. 3 while a summary of half-wave potentials for electrooxidation and electroreduction is given in Table 2 which also includes the potentials for the related vanadium-oxo phthalocyanines [(Bu)4Pc]VO and (F16Pc)VO [9, 10] and phthalocyanine analogs, [(TBP)8Cz(H)]VO [16] and (TPP)VO [25].

Compounds 1 and 2 both undergo two one-electron reversible reductions which are located at E1/2 = -0.51 and -0.97 V for 1 and -0.62 and -1.12 V for 2. A more negative irreversible reduction is also observed for 1 at Epc = -1.94 V and for 2 at E pc = -2.07 V. Only one oxidation was reported for previously studied vanadium-oxo phthalocyanines [9, 10], but two oxidations are observed for the presently investigated compounds. The first of these is reversible for both compounds (Fig. 3). Compound 2 has stronger electron-donating substituents than 1; therefore it is

harder to reduce and easier to oxidize than 1 and its redox potentials are all shifted negatively by 0.11-0.18 V as compared to 1 (Fig. 3).

The potential difference, ΔEred(1-2), between the first two reductions is 0.46 V for 1 and 0.50 V for 2. These separations are the same as those obtained for [(Bu)4Pc]VIVO (0.50 V), (TPP)VIVO (0.52 V) and [(Bu)4Pc]TiIVO (0.50 V) under the same experimental conditions (see Table 2). The HOMO-LUMO gap is 1.45 V for 1 and 1.38 V for 2 and is comparable with the gaps of [(Bu)4Pc]VIVO (1.52 V) and [(Bu)4Pc]TiIVO (1.37 V). However, it is much smaller than the 1.63 V for (F16Pc)VIVO and 1.99 V for (TPP)VIVO (Table 2). It is known that the two reductions and one oxidation of [(Bu)4Pc]VIVO, [(Bu)4Pc]TiIVO and (TPP)VIVO are all macrocycle-centered reactions [9, 25]. Compounds 1 and 2 have similar electrochemical behavior. The first oxidation of these two complexes is phthalocyanine-ring centered and leads to formation of a π-cation

Fig. 3. Cyclic voltammograms of (a) compound 2 and (b) compound 1 in DMF, 0.1 M TBAP. Small peaks indicated by * are caused by impurities

Fig. 4. Cyclic voltammograms of compound 2 in DMF, 0.1 M TBAP at different scan rates of (a) 20, (b) 50, (c) 100, (d) 200 and (e) 500 mV.s-1

Z. JIANG ET AL.358

radical. The first two reductions for 1 and 2 are also ring-centered and lead to formation of a π-anion radical and dianion upon the first and second reductions in DMF, 0.1 M TBAP.

Cyclic voltammetric measurements of 2 were also carried out in DMF containing 0.1 M TBAP at different scan rates (20-500 mV.s-1). The cyclic voltammograms are shown in Fig. 4. Linear relationships between the peak current (ip) and the square root of the scan rate (υ1/2) are seen for the first two reversible reductions and for the first oxidation of this compound (Fig. 5). These results indicate that each redox process is a diffusion-controlled electrode reaction.

Spectroelectrochemistry

Thin-layer UV-visible spectroelectro-chemistry for complexes 1 and 2 was carried out in DMF, 0.1 M TBAP. Similar spectroelectrochemical data was obtained for both complexes. As an example, the spectral changes obtained for 2 upon the first oxidation and the first, second and third reductions are shown in Figs 6 and 7.

Upon the first reduction of 2 at -0.90 V, the Q band at 746 nm disappears while two bands at 618 and 1031 nm grow in (Fig. 6a),

consistent with formation of a phthalocyanine π-anion radical. Based on the final spectrum obtained after the first oxidation at 1.00 V (see Fig. 6b), the product for the oxidation of 2 is proposed to be a phthalocyanine π-cation radical. Spectral changes for the phthalocyanine ring-centered reduction and ring-centered oxidation are both reversible and the initial spectrum can be recovered when the potential is returned to 0.0 V. The π-anion and π-cation radicals are both stable on the thin-layer spectroelectrochemical time scale. The spectral changes upon further reductions at -1.40 and -2.20 V for complex 2 are shown in Fig. 7. These two reductions are also considered to be the macrocycle ring-centered and lead to formation of the species, [2]2- and [2]3-.

ESR characterization

Similar ESR spectra are observed in DMF solutions (173 K) and in the solid state for [(OC6H3(t-Bu)2)4Pc]VO 1 and [(OC8H17)4Pc]VO 2. Examples of the ESR spectra for these complexes in DMF (173 K) are shown in Fig. 8. The illustrated spectra are similar to each other and confirm the oxidation state assignment as +4, giving rise to a VIV=O (d1, S = 1/2) ESR spectrum for both complexes. The peaks of the spectra are clearly due to the 51V (I = 7/2) hyperfine interaction characterized by g// = 1.981, g⊥ = 2.015 and A// = 167.0 (G), A⊥ = 59.0 (G) for complex 1 and g// = 1.982, g⊥ = 2.015 and A// = 169.6 (G), A⊥ = 59.6 (G) for complex 2. The g and A values of the ESR spectra for

Fig. 5. Plot of peak current (ip) vs the square root of scan rate (υ1/2) for (a) the first and second reductions and (b) the first oxidation of compound 2 in DMF, 0.1 M TBAP

Fig. 6. Thin-layer UV-visible spectral changes of compound 2 obtained during (a) the first reduction at -0.90 V and (b) the first oxidation at 1.00 V in DMF, 0.1 M TBAP

1 and 2 are comparable with values of non-substituted VIV=O phthalocyanine [26]. The ESR spectra of 1 and 2 are also in good agreement with other monomeric phthalocyanine analogs, i.e. the porphyrin (TPP)VIVO [25], the corrolazine [(TBP)8Cz(H)]VIVO [16] and the

octakis(hexylthio)vanadylporphyrazine [13]. If a dimer was formed for a vanadium-oxo phthalocyanine complex, an ESR spectrum with fifteen lines should be observed as repor-ted for (F16Pc)VO [10]. The ESR spectra obtained for 1 and 2 in DMF at 173 K indicate that only monomeric complexes exist and no dimer is formed under the given experimental conditions.

CONCLUSIONTwo vanadium-oxo phthalocyanines with

aryloxy or alkoxy substituents on the four α-positions were synthesized and characterized by UV-visible, IR, MS, ESR spectroscopy and electrochemistry. The spectra of LB film indicate that the investigated complexes are arranged in an edge-to-edge form. These vanadium-oxo complexes have high solubility in both polar and non-polar organic solvents. UV-vis spectral and ESR data show that no aggregation occurs and only monomers exist under the given experimental conditions. Three reductions and two oxidations can be

observed in DMF, 0.1 M TBAP. The HOMO-LUMO gaps for these complexes range from 1.38 to 1.45 V. The first reduction and first oxidation are both phthalocyanine ring-centered electrode processes and lead to the formation of π-anion and π-cation radicals.

Acknowledgements

The financial support of the Nature Science Research Foundation of Fujian Province in China (Project E0310007) and the Robert A. Welch Foundation (K.M.K. E-680) are highly appreciated.

REFERENCES 1. The Porphyrin Handbook, Kadish KM, Smith

KM and Guilard R, Eds., Academic Press: New York, 2003; Vol. 19.

2. Phthalocyanines, Properties and Applications, Leznoff CC and Lever ABP, Eds., VCH: New York, 1989-1996, Vols I-IV.

3. Thomas AL, Phthalocyanine Research and Applications, CRC Press: Boston, 1990.

4. Snow AW. in The Porphyrin Handbook, Kadish KM, Smith KM, Guilard R, Eds., Academic Press: New York, 2003; Vol. 17, Chapter 109, pp 130-176.

5. Shen YJ. The Synthesis and Applications of Phthalocyanines, Chemical Industry Press: Beijing, 2001.

6. Gu DH, Chen QY, Shu JP, Tang XD, Gan FX,

Fig. 8. ESR spectra of complexes 1 (a) and 2 (b) in DMF at 173 K. ESR parameters: microwave frequency, 9.516 GHz; incident microwave power, 20.3 mV; modulation frequency, 100 kHz; modulation amplitude, 10.0 G; receiver gain, 4.0 × 104

Fig. 7. Thin-layer UV-visible spectral changes obtained for compound 2 during (a) the second reduction at -1.40 V and (b) the third reduction at -2.20 V in DMF, 0.1 M TBAP

Z. JIANG ET AL.360

Shen SY, Liu K and Xu HJ. Thin Solid Films 1995; 257: 88.

7. Guo L, Ma G, Liu Y, Mi J, Qian S and Qiu L. Appl. Phys. B 2002; 74: 253.

8. Honeybourne CL and Odannell J. Analytical Proceedings 1991; 28: 333.

9. Lever ABP, Licoccia S, Magnell K, Minor PC and Ramaswamy BS. Adv. Chem. Ser. 1982; 201: 237.

10. Handa M, Suzuki A, Shoji S, Kasuga K and Sogabe K. Inorg. Chim. Acta 1995; 230: 41.

11. Tian MQ, Zhang YD, Wada T and Sasabe H. Dyes and Pigments 2003; 58: 135.

12. Li BY, Wang JD, Yang SL and Chen NS. Chinese J. Synth. Chem. 2003; 11: 138.

13. Ozturk R, Guner S, Aktas B and Gul A. Synth. React. Inorg. Met.-Org. Chem. 2001; 31: 1623.

14. Walters MA. Appl. Spectrosc. 1983; 37: 299.15. Licoccia S, Paolesse R, Tassoni E, Polizio F and

Boschi T. J. Chem. Soc., Dalton Trans. 1995; 3617.

16. Fox JP, Ramdhanie B, Zareba A, Czernuszewicz RS and Goldberg DP. Inorg. Chem. 2004; 43:

6600.17. Torres T. J. Porphyrins Phthalocyanines 2000;

4: 325.18. George RD, Snow AW, Shirk JS and Barger

WR. J. Porphyrins Phthalocyanines 1998; 2: 1.19. Sommeraurer M, Rager C and Hanack M. J.

Am. Chem. Soc. 1996; 118: 10085.20. Kasuga K, Hayashi H and Handa M. Chem. Lett.

1991; 1877.21. Kasuga K and Tsutsui M. Coord. Chem. Rev.

1980; 32: 67.22. Harriman A and Richoux MC. J. Chem. Soc.,

Faraday Trans. 2 1980; 76: 1618.23. Griffiths CH, Walker MS and Goldstein P. Mol.

Cryst. Liq. Cryst. 1976; 33: 149.24. Kobayashi N, Ogata H, Nonaka N and

Lukʼyanets EA. Chem. Eur. J. 2003; 9: 5123.25. Kadish KM, Sazou D, Araullo C, Liu YM,

Saoiabi A, Ferhat M and Guilard R. Inorg. Chem. 1988; 27: 2313.

26. Sato M and Kwan T. J. Chem. Phys. 1969; 50: 558.

Copyright of the works in this Journal is vested with World Scientific Publishing. Thearticle is allowed for individual use only and may not be copied, further disseminated, orhosted on any other third party website or repository without the copyright holder’swritten permission.

Synthesis, spectral and electrochemical characterization of non-aggregating α-substituted...

Documents

Transcript of Synthesis, spectral and electrochemical characterization of non-aggregating α-substituted...

Handbook of electrochemical impedance spectroscopy.pdf

Journal of Industrial and Engineering Chemistry · 2017. 10. 23. · Electrochemical characterization and thermodynamic tendency of β-Lactoglobulin adsorption on 3D printed stainless

Electrochemical Equilibrium – Electromotive Force

ORR performance Test. electrode system on an electrochemical ... · electrode system on an electrochemical workstation (CHI 660D) in 0.1 M KOH electrolyte. Then 8 μL of the homogeneous

10.626 Lecture Notes, Impedance spectroscopy · PDF fileImpedance spectroscopy ... we will see that electrochemical double layers can be modeled as parallel ... 10.626 Lecture Notes,

Electrochemical Behaviour of Native and Denatured β-Sheet ... · Primarily, the basic electrochemical behaviour of prion and its redox system was observed using CV where 3 various

Electrochemical Phenomena Eh and pE Approaches Redox Reactions pE-pH Diagrams Flooded Soils.

Electrochemical Preparation of a Novel Elec- troactive

An inspection of the runoff of an electrochemical grinding … · The electrochemical grinding process (ECG) is a subset of the machining family known as electrochemical machining

Electrochemical Detection in HPLC

Supplementary Materials Catalyzed by (Imido)vanadium(IV ... · A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps. Organometallics 2016 , 35 , 2286–2293. (b)

Electrochemical Impedance Spectroscopy: Low Z Systems · EIS Relevance to Energy Storage and Conversion (ESC) • Materials research before building ESC devices give plenty of information

Lattice Dynamics of β-V O : Raman Spectroscopic Insight ... · Lattice Dynamics of β-V 2O 5: Raman Spectroscopic Insight into the Atomistic Structure of a High-Pressure Vanadium

HIGH EFFICIENCY WIRELESS ELECTROCHEMICAL ACTUATORS: DESIGN …biomems.usc.edu/publications/2011/2011_MEMS_echem_actuator.pdf · of the wireless system (Fig. 11). CONCLUSION We demonstrated

Metal …downloads.hindawi.com/archive/2011/605913.pdfISRN Condensed Matter Physics 3 Table 1: Parameters of vanadium oxides. Oxide T t,K αm∗/m e VO Metal — — V 2O 3 150 0.462

oxo cms portal full

PPAR · 2020-07-09 · PPAR Inhibitors, Agonists, Antagonists, Activators & Modulators 13-Oxo-9E,11E-octadecadienoic acid Cat. No.: HY-N5097 13-Oxo-9E,11E-octadecadienoic acid, an

E.P.R. studies of the phase transitions in -phase vanadium … · 2017-09-23 · 2014 The 03B2 phase vanadium bronzes NaxV2O5 have been studied by E.P.R. Two transi-tions in magnetic

Electrochemical Sensors Based on Architectural Diversity ...

Inorganic nanostructures for photo-electrochemical and photo-catalytic water splitting Frank E. Osterloh Chem. Soc. Rev., 2013, 42, 2294.