Selective metal sensor phthalocyanines bearing non-peripheral functionalities: Synthesis, spectroscopy, electrochemistry and spectroelectrochemistry

Polyhedron 28 (2009) 257–262

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Selective metal sensor phthalocyanines bearing non-peripheral functionalities: Synthesis, spectroscopy, electrochemistry and spectroelectrochemistry Mehmet Kandaz a,*, Meryem N. Yarasir a, Atıf Koca b a b

Sakarya University, Department of Chemistry, 54140 Esentepe, Sakarya, Turkey Marmara University, Department of Chemical Engineering, Faculty of Engineering, 34722 Göztepe, Istanbul, Turkey

a r t i c l e

i n f o

Article history: Received 12 September 2008 Accepted 11 November 2008 Available online 6 January 2009 Keywords: Phthalocyanines Metal sensor Aggregation Electrochemistry Spectroelectrochemistry

a b s t r a c t A novel alcohol-soluble ionophore ligand and its non-peripherally tetrasubstituted functional 1,8,15,22tetrakis(6-hydroxyhexylsulfanyl) metallophthalocyanines M[Pc(a-SC6H12OH)4] (M = Cu(II), Zn(II), Co(II); Pc = phthalocyanine) are reported. The aggregation and cation binding behaviors of the phthalocyanine compounds in the presence of soft AgI and PdII metal ions were investigated by using UV–Vis spectroscopy. The new compounds have been characterized by elemental analysis, IR, 1H, 13C NMR, UV/Vis spectroscopy, ESI and MALDI–TOF–MS mass spectra. Voltammetric and in-situ spectroelectrochemical studies show that while copper and zinc phthalocyanine complexes give well-defined ring-based reduction and oxidation processes, the cobalt phthalocyanine gives both metal-based and ring-based redox processes which have reversible and diffusion controlled character. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction The benefit of phthalocyanines (Pcs) in terms of technological applications is beyond question [1,2]. The family of functional phthalocyanines has been an interesting target for chemists for the development of further chemical reactions on Pc complexes [3,4]. Functional Pcs perturbs the Pcs optical transitions by shifting the absorption from the visible to near-IR or UV-region. Phthalocyanines bearing thia functionalities show optical changes when they bind transition metal ions, while crown-ether substituted ones are well-suited to bind alkaline and alkaline-earth metal ions [5,6]. Although several Pcs bearing different substituents either on the b position or at an axial position have been synthesized and characterized [5,7], papers on the synthesis, electrochemistry and spectroelectrochemistry of non-peripherally functional phthalocyanines are scarce because of the preparation and purification required [8]. In the past few years we have directed our attention to the construction of phthalocyanine-based functional systems [3,9,10]. The introduction of functional groups having rich electron-donor units on the phthalocyanine ring is not only expected to improve its solubility but also to enhance optical or electrochemical properties of the phthalocyanine. In this study, we therefore report a new ligand and its nonperipherally a-substituted MPcs, M[Pc(a-SC6H12OH)4] {M = Cu(II) (2), Zn(II) (3), Co(II) (4)}. The cation binding capabilities of the functional substituents on the periphery of MPcs (2)–(4) as well

* Corresponding author. Tel.: +90 2642955946; fax: +90 2642955950. E-mail address: [email protected] (M. Kandaz). 0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.11.035

as voltammetric and in-situ spectroelectrochemical characterization are also reported. 2. Experimental Chloroform (CHCl3), 4-nitrophthalonitrile, tetrahydrofuran (THF), tetrabutyl ammoniumperchlorate (TBAP), Zn(OAc)2, CuCl2, CoCl2 and all other reagents were purchased from Alfa Aesar and were used as received. The purity of the products was tested in each step by TLC (thin-layer chromatography) (SiO2, CHCl3, hexane and MeOH). FT-IR (Fourier transform infrared) spectra were recorded on a Perkin–Elmer spectrophotometer with samples were dispersed in KBr discs. Chromatography was performed with silica gel (Merck grade 60 and sephadex) from Aldrich. Elemental analysis (C, H and N) was performed at the instrumental Analysis Laboratory of Marmara University. Time- and applied-resolved UV–Vis spectra were recorded on an Agilent Model 8453 diode array spectrophotometer. 1H NMR, and 13C NMR spectra were recorded on a Bruker 300 spectrometer instrument. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were carried out with a Gamry Reference 600 potentiostat/galvanostat controlled by an external PC and utilizing a three-electrode configuration at 25 °C. The working electrode was a Pt disc with a surface area of 0.071 cm2. The surface of the working electrode was polished with a diamond suspension before each run. A Pt wire served as the counter electrode. A saturated calomel electrode (SCE) was employed as the reference electrode and this was separated from the bulk of the solution by a double bridge. Ferrocene was used as an internal reference. Electrochemical grade

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2.1. Synthesis

and monitored by TLC (CHCl3) under an inert atmosphere at 40– 45 °C for 2 days. After the reaction mixture was cooled to room temperature, it was poured into ca. 300 cm3 ice-water. The creamy precipitate that formed was filtered and washed with water until the washings became neutral. The crude product was dissolved in CHCl3 and washed with 5% NaHCO3 to remove the unreacted starting thiol compounds. The creamy solution was then dried with anhydrous Na2SO4, and filtered. The solvent, CHCl3, was removed under reduced pressure. The final product was chromatographed over a silica gel column using a mixture of CHCl3: MeOH (100/5) as eluent, giving a hydroscopic oily solid. Finally the pure powder was dried in vacuum. Yield: 0.93 g (61.89 %). M.p.: 77 °C. IR (thin film) /cm1: 2236 (– CN), 3280 (CH2–OH), 3080, 3045 (Ar–H), 2933, 2885, 2854 (AliphCH2) 1707 (H–O  H, weak), 1585 (s), 1555, 1476, 1384, 1277, 1145, 1067, 980, 852, 735, 570. 1H NMR ([D6]-DMSO) d (ppm): 7.85–7.62 (m, 3H, Ar–H, Phenyl Ar–H H3, H4 and H5), 4.19 (t, br, –CH2–OH, D2O exchangeable), 3.55 (t, 2H, –CH2OH), 2.85 (CH2– CH2–S–), 1.65 (m, 2H, CH2–S–Ar), 1.50 (m, 2H, CH2CH2CH2–OH), 1.37 (m, 2xCH2CH2CH2). 13C NMR (ATP test) (300 MHz, [D6]DMSO) d (ppm): 143.23, 135.45, 132.76, 130.09, 116.12, 115.16, 116.95, 116.82, 62.76 (–CH2 OH), 40.42 (DMSO), 37.16 (S-CH2), 33.40 (CH2CH2OH), 29.12 (SCH2CH2), 28.80 (SCH2CH2CH2), 25.26 (CH2CH2CH2CH2OH). Anal. Calc. for C14H16N2OS (%): C, 64.62; H, 6.15; N, 10.77. Found (%): C, 64.04; H, 6.05; N, 10.28%. MS (MALDI–TOF): m/z: 262.3 [M]+ , 283.1 [M+Na]+.

2.1.1. 30 (6-hydroxyhexylthio)-1,2-dicyanobenzene (1) 6-Mercapto–1-hexanol (1.55 g, 12.00 mmol, excess) was dissolved in dry DMF and finely ground anhydrous K2CO3 (2.40 g, 17.00 mmol) was added. Then 3-nitrophthalonitrile (2.00 g of 11.56 mmol) was added to this mixture dropwise at 35–40 °C under a N2 atmosphere. The reaction mixture was stirred efficiently

2.1.2. 1(4),8(11),15(18),22(25)-(6-Hydroxyhexylthio)zinc(II)phthalocyanine (2) 30 -(6-hydroxyhexylthio)-1,2-dicyanobenzene (1) (0.25 g, 0.96 mmol) and anhydrous ZnCl2 (0.022 g), in the presence of quinoline and 1,8-diazabicyclo [5.4.0.] undec–7-ene (DBU, 0.05 ml) as a strong base (Scheme 1), were heated to reflux in a sealed tube

tetrabutylammonium perchlorate (TBAP) in extra pure dimethylsulfoxide (DMSO) was employed as the supporting electrolyte at a concentration of 0.10 mol dm3. High purity N2 was used to remove dissolved O2 prior to each run and to maintain a nitrogen blanket during the measurements. IR compensation was also applied to the CV scans to minimize the potential control error. The spectroelectrochemical measurements were carried out with an Ocean-optics QE65000 diode array spectrophotometer equipped with a potentiostat/galvanostat utilizing the three-electrode configuration of a thin-layer quartz spectroelectrochemical cell at 25 °C. The working electrode was Pt tulle. A Pt wire counter electrode separated by a glass bridge and a SCE reference electrode separated from the bulk of the solution by a double bridge were used. Matrix-assisted laser desorption/ionization-time-of-flight (MALDI–TOF) mass spectra were measured using a Bruker Autoflex III mass spectrometer equipped with a nitrogen UV-Laser operating at 337 nm. Spectra were recorded in the reflectron mode with an average of 50 shots. An a-cyano 4-hydroxycinnamicacid (CHCA) (20 mg/mL in THF) matrix was used. MALDI samples were prepared by mixing the complex (2 mg/mL in THF) with the matrix solution (1:10 v/v) in a 0.5 mL eppendorfÒ micro tube. Finally, 1 lL of the mixture was deposited on the sample plate, dried and then analyzed.

OH

CN NC

NC

HS

NO2

S

OH

NC

i

1

ii

RS N RS

N

N M

N

N N

N

SR

N SR R=

OH

M= Zn(2), Cu(3), Co(4) Scheme 1. Synthetic route of the 1,8,15,22-tetrakis{6-hydroxyhexylsulfanyl) metallophthalocyanines M[Pc(a-SC6H12OH)4] {M = Zn(II) (2), Cu(II) (3), Co(II) (4)}. (i) K2CO3, 6mercapto-1-hexanol, DMF, 40–45 °C, 2 days. (ii) Anhydrous, Zn(O2CMe)2, CuCl2, CoCl2, DBU.

M. Kandaz et al. / Polyhedron 28 (2009) 257–262

under a N2 atmosphere for 6 h. The color of the mixture turned green-blue over this time. After heating for an additional 3 h, the green–blue product was cooled to room temperature. The crude product formed was washed several times, successively with iPrOH and then cold CH3CN, to remove impurities. Finally, the product was further purified by silica gel chromatography {CHCl3 and then with CHCl3/MeOH (20:1 v/v)}. After washing the resulting oily product with copious amounts of hexane, diethylether and i-PrOH, finally it was dried in vacuum. This product is soluble in MeOH, THF, DMF, DMSO, pyridine and insoluble in diethylether. Yield of 2: 0.087 g (32.80%). Anal. Calc. for C56H64N8O4S4Zn (1105.0 g/mol): C, 60.81; H, 5.79; N, 10.14. Found: C, 60.28; H, 5.80%; N, 9.77. IR (KBr) m/cm1: 3284 (br, H-bonded), 2926, 2853, 1726 (H–O  H, weak), 1611 (w), 1598, 1484, 1430, 1366, 1223, 1215, 1138, 1066, 1032, 912, 825, 757, 735. 1H NMR ([D6]-DMSO) d (ppm): 7.88–7.60 (m, 12H, Ar-H, Phenyl Ar-H H3, H4 and H5), 4.21 (t, broad, 4H, –CH2–OH, D2O exchangeable), 3.55 (t, 8H, – CH2OH), 2.95 (8H, CH2–CH2–S–), 1.65 (m, 8H, –CH2CH2–S–Ar), 1.50 (m, 8H, CH2CH2CH2–OH), 1.37 (m, 2xCH2CH2CH2OH). UV/Vis (THF, kmax/nm: 709 (p–p*), 668 (agg), 656 (n-p*), 335 (deeper, p– p*). MS (MALDI–TOF, a-cyano 4-hydroxycinnamicacid (CHCA) as matrix): m/z (100 %): 1105 [M+H]+. 2.1.3. 1(4),8(11),15(18),22(25)-(6-Hydroxyhexylthio)copper(II)phthalocyanine (3) The same procedure as described for the preparation of 2, starting from 1 (0.150 g, 0.576 mmol) and CuCl2 (0.021 g, 0.170 mmol), was used to prepare compound 3. Yield of 3: 0.06 g (24.16%). Anal. Calc. for C56H64N8O4S4Cu (1103.5 g/mol): C, 60.90; H, 5.80; N, 10.15. Found: C, 60.69; H, 5.77; N, 9.58%. IR (thin film) m/cm1: 3250 (H-bonded, OH), 3015, 2975, 2952, 2854, 1727 (H–O  H, weak), 1655 (w), 1598, 1432 (w), 1366 (s), 1360, 1313, 1224, 1218, 1137, 1118, 1034, 910, 887, 873, 811, 742, 687. UV/Vis (THF, kmax/nm: 710 (p–p*), 662 (agg), 647 (n–p*), 441 (CT), 333 (deeper, p–p*). MS (MALDI–TOF, CHCA as matrix): m/z (100%): 1104 [M+H]+. 2.1.4. 1(4),8(11),15(18),22(25)-(6-Hydroxyhexylthio)cobalt(II)phthalocyanine (4) The same procedure as described for the preparation of 2, starting from 1 (0.150 g, 0.576 mmol) and CoCl2 (0.021 g, 0.170 mmol), was used to prepare compound 4. Yield of 4: 0.07 g (27.30%). Anal. Calc. for C56H64N8O4S4Co (1099 g/mol): C, 61.15; H, 5.82; N, 10.19. Found: C, 60.56; H, 5.56; N, 9.59%. IR (KBr thin film) m/cm1: 3243 (H-bonded, OH), 3026, 2973, 2928, 2847, 1722 (H–O  H, weak), 1600 (w), 1520, 1431 (w), 1360 (s), 1318, 1233, 1210, 1103, 1044, 933, 873, 781, 750, 694. UV/Vis (THF, kmax/nm: 695 (p–p*), 654 (agg), 629 (w, n-p*), 327 (deeper, p–p*). MS (MALDI–TOF, CHCA as matrix): m/z (100%):1100 [M+H]+.

259

quinoline and DBU as a strong base (Scheme 1), followed by chromatographic purification on silica gel columns. The purification steps were tedious because of the peripheral polar functional end-group. The new compounds were characterized by UV–Vis, IR, NMR spectroscopies, MALDI–TOF mass spectra and elemental analysis. All the analytical and spectral data are consistent with the predicted structures. The sharp peak in the IR spectra for the –C„N vibrations of 1 at 2230 cm1 disappeared after conversion into the MPcs, indicative of the MPcs formation. A primary aliphatic –OH peak at around 3280 cm1 and the remainder of the spectra for 2–4 are closely similar and diagnosed easily. Broad signals in the NMR spectrum of 2 are probably due to chemical exchange associated with aggregation–disaggregation equilibria which occurred at the high concentrations used in the NMR measurements. A broad signal belonging to primary aliphatic exchangeable –OH protons appeared at ca. 4.21 ppm, and this disappeared after addition of D2O. Splitting of the aromatic protons in the downfield region is less for a-substituted compounds when compared to b-substituted ones [12–15]. The UV/Vis spectra of the MPcs 2–4 exhibited characteristic absorptions in the Q-band region at around 695–710 nm, attributed to the p–p* transition from the HOMO (highest occupied molecular orbital) to the LUMO (lowest unoccupied molecular orbital) of the Pc2 ring, and in the B band region (UV region) at around 300–400 nm, arising from deeper p–p* transitions [14]. In the UV/Vis absorption spectra of MPcs 2–4, the Q-band absorptions were observed as a single band with high intensity at 709, 710 and 695 nm respectively. There was also a shoulder at the slightly higher energy side of the Q-band at 668, 662 and 654 nm for each phthalocyanine respectively. The Q-band absorptions are shifted to the lower energy side as a result of the electron-donating thioether substituents on periphery of the Pcs compared to those of MPcs bearing oxo substituted moieties, whereas the position of the Soret-like p–p* bands of all the MPcs are slightly shifted [5,6,9,14,15]. The Q-band of the a (non-peripheral) substituted Pcs is red-shifted by about 20 nm, when compared to the corresponding b (peripheral)-substituted complexes in the same solvent [9,11–13,14]. The observed red spectral shift is typical of Pcs bearing substituents at the a positions and has been explained by the linear combinations of the atomic orbital (LCAO) coefficients at

3. Results and discussion 3.1. Synthesis and characterization The introduction of 6-mercapto-1-hexanol groups, having rich electron-donor units, on the Pc ring is not only expected to improve the solubility of phthalocyanines in polar medium such as MeOH, EtOH, THF, DMF, DMSO and i-PrOH, but also to enhance the optical or electrochemical properties of the phthalocyanine. In the present work, 3’-(6-hydroxyhexylthio)-1,2-dicyanobenzene (1) can be readily synthesized by nucleophilic aromatic substitution reactions of 6-mercapto-1-hexanol on 3-nitrophthalonitrile [11]. MPc complexes (2–4) were obtained from the reaction of 1 with the appropriate anhydrous metal salts in the presence of

Fig. 1. Positive ion and reflectron mode MALDI–MS spectrum of 4 obtained in a-cyano-4-hydroxycinnamic acid (CHCA) as the MALDI matrix. Inset spectrum shows the expanded molecular mass region of 4.

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A

-40

R2

R1

I / μA

-20

0 -1

50 mVs -1 100 mVs -1 250 mVs -1 500 mVs

20

O1 40

60

1.5

B

O2

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

-20

-10

I / μA

Fig. 2. UV–Vis spectra of 3 in THF/MeOH (90/10 (v/v)) during titration with AgI (in MeOH).

the a positions for the HOMO [12,13]. As a result, the HOMO level is destabilized more for an a position than a b position. Moreover, the B bands of the complexes in the UV/Vis absorption spectra are broad due to the superimposition of the B1 and B2 bands in the 325–340 nm regions. The mass spectra of 2–4 confirmed the proposed structures. The protonated molecular ion peaks (MALDI matrix; a-cyano–4hydroxycinnamic acid (CHCA)) were easily identified at m/z: 1104.20 [M+H]+ for 2, 1105.78 [M+H]+ for 3 and 1100.30 [M+H]+ for 4 (Fig. 1) and they exactly overlapped with the mass of the complexes calculated theoretically from their elemental compositions [9].

0

R1

O1

O2

R2

10

20

30 1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

E / V vs.SCE Fig. 3. CVs (A) and DPVs (B) of 4 (5.00  104 mol dm3) at various scan rates on Pt working electrode in DMSO/TBAP electrolyte system. DPV parameters: pulse time 50 ms, pulse size 100 mV, step size 5 mV, sample period 100 ms.

Table 1 Voltammetric data of the complexes 2–4 with the related metallophthalo cyanines for comparison. Complex 2

3

4

g

CoPc CoPc i ZnPc i CuPc j ZnPc j CoPc h

Ring oxidations a

E1/2 b DEp (mV) c Ipa/Ipc a E1/2 b DEp (mV) c Ipa/Ipc a E1/2 b DEp (mV) c Ipa/Ipc f E1/2 (in DMSO) f E1/2 (in DMSO) f E1/2 (in DMSO) f E1/2 (in DCM) f E1/2 (in DCM) f E1/2 (in DCM)

0.34 – –

0.56 85 0.89 0.28 88 0.55 0.90e 71 – 0.99 0.77 0.56 0.85

MII/MIII

0.40 81 0.75 0.46 0.49

0.45

MII/MI

0.43 67 1.00 0.36 0.36

0.42

Ring reductions

d

0.91 75 0.91 0.96 80 0.85 1.39 93 0.97 1.27 1.27 0.71 0.91 0.75 1.30

1.47

DE1/2

1.36 80 0.88 1.17 85 0.82

Ref. tw

1.24 tw 0.83 tw

1.83e 1.10 1.27 1.16

1.43

0.82 0.85 1.48 1.47 1.60 0.87

9 17 [19] [19] 20 20

Tw – This work. a E1/2 = (Epa + Epc)/2 at 0.100 Vs1 scan rate. b DEp = Epa + Epc at 0.100 Vs1 scan rate. c Ipa/Ipc for reduction, Ipc/Ipa for oxidation processes at 0.100 Vs1 scan rate. d DE1/2 = E1/2 (first oxidation) – E1/2 (first reduction) = HOMO–LUMO gap for metallophthalocyanines having an electro-inactive metal center (metal to ligand (MLCT) or ligand to metal (LMCT) charge transfer transition gap for MPc having a redox active metal center). e The process is recorded with DPV. f Potentials were given versus SCE. g Substituted with tetrakis(6-hydroxyhexylsulfanyl) moieties. h Substituted with tetrakis-6-(-thiophene-2-carboxylate)-hexylthio moieties. i Substituted with tetra-tricarboethoxyethyl moieties. j Substituted with tetrapentafluorobenzyloxy moieties.

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3.2. UV/Vis spectroscopic titrations We have employed UV/Vis spectroscopic titrations to monitor the capability of our MPcs in sensing/coordinating transition metal ions of different sizes. The room temperature gradual addition (ll) of AgI and PdII to solutions of 2 and 3 caused a gradual color change, from blue–green to intractable dark-green, suggesting complex formation of the Mpcs with AgI and PdII. Addition of small increments of AgI to 3 (Fig. 2) leads to the gradual disappearance of monomeric species, which show absorptions at 710 and 708 nm, and simultaneously enhances the intensity of the oligomeric aggregated species at around 662 and 668 nm. Similar spectroscopic changes were observed during the titration of 3 with PdII, and 2 with AgI and PdII. This type of spectroscopic behavior probably results from the complexation of AgI and PdII with the Pc complexes. These spectroscopic changes indicate the coordination of AgI and PdII with the S donor atoms of the phthalocyanines and the formation of polymer units due to the aggregation of the complexes [2,6,9]. 3.3. Electrochemical and spectroelectrochemical measurements The solution redox properties of the complexes 2–4 were studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in DMSO on a platinum electrode. Table 1 lists the assignments of the redox couples recorded and the estimated electrochemical parameters, which included the half-wave peak potentials (E1/2), the ratio of anodic to cathodic peak currents (Ip,a/Ip,c), the peak to peak potential separations (DEp) and the difference between the first oxidation and first reduction processes (DE1/2). When we compare the redox potentials of 2–4 with those of the unsubstituted MPcs [16], MPcs carrying tetrakis-(6-hydroxyhexylsulfanyl) [9] and tetrakis-6-(-thiophene-2-carboxylate)-

hexylthio moieties [17], it is clearly shown that the redox potentials of 2–4 shift to negative potentials due to the electron releasing effect of the tetrakis-(6-hydroxyhexylsulfanyl) substituents on the a position of the complexes (Table 1). Within the electrochemical window of TBAP/DMSO, 2 and 3 undergo a one-electron oxidation (two oxidations for 3) and two one-electron reduction reactions having reversible and diffusion controlled mass transfer processes. Because of the electro-inactive metal center of the complexes, all of these processes are attributed to successive removal of electrons from, or addition of electrons to, the macrocycle orbitals. Fig. 3 shows the CV and DPV of CoPc (4) as a representative example of the redox behaviors of the complexes. Within the electrochemical window of TBAP/DMSO, 4 undergo two reversible oneelectron oxidation processes and two reversible one-electron reduction processes. The first reduction and first oxidation processes of 4, recorded at 0.43 and 0.40 V, could be easily assigned to the CoII/CoI and CoII/CoIII redox couples respectively and the remaining processes to the phthalocyanine ring. Assignments of the redox couple are confirmed by the spectroelectrochemical measurements given below. For the couples, the DEp values changed from 60 to 120 mV with scan rates from 10 to 500 mVs1 ðDEp0 , 60 to 110 mV, were obtained for the ferrocene reference), supporting reversible electron transfer. Reversibility is illustrated by the similarity in the forward and reverse DPV scans (Fig. 3B) [18]. Unity of the Ip,a/Ip,c ratio at all scan rates indicated the purely diffusion controlled mass transfer of the complex. Spectroelectrochemical studies were employed to confirm the assignments in the CVs of the complexes. The complexes 2 and 3 have redox inactive metal centers. Therefore, in-situ UV–Vis spectral changes of 4 are only given as a representative example of the spectral changes of a MPc having a redox active metal center (Fig. 4). Fig. 4A shows the in-situ UV–Vis spectral changes during

B

Abs.

Abs.

A

300

400

500

600

700

800

900

C

300

400

500

600

700

800

900

500

600

700

800

900

Abs.

D

300

400

500

600

700

Wavelength (nm)

800

900

300

400

Wavelength (nm)

Fig. 4. In-situ UV–Vis spectral changes of 4 (A) Eapp = 0.50 V. (B) Eapp = 1.45 V. (C) Eapp = 0.45 V. (D) Eapp = 1.00 V.

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the controlled potential reduction of 4 at 0.50 V, corresponding to the redox process labelled R1. The Q-band at 695 nm shifts to 725 nm, while two new bands at 390 and 477 nm appear, as the reduction process continues. At the same time, the B band shifts from 327 to 317 nm with decreasing intensity. The bands at 390 and 477 nm and the red shifting of the Q-band indicate the formation of the [CoIPc2]1 species and confirm the CV assignment of the couple R1 to the [CoIIPc2]/[CoIPc2]1 process [20–25]. Clear isosbestic points at 311, 365, 571, 715 and 764 nm in the spectra and a color change from blue to greenish yellow were observed during this process. Fig. 4B shows the spectral changes during the second reduction process of 4. During this process, while the Q-band at 725 nm, the band at 390 nm and the B band at 317 nm decrease in intensity, a new band at around 557 nm appears. Clear isosbestic points at 341, 381, 484, 640 and 780 nm in the spectra and a color change from greenish yellow to red were observed during this process. These spectral changes are characteristic of a ring reduction process and are easily assigned to the reduction of the [CoIPc2]1 species to [CoIPc3]2 at the potential of the couple R2. Fig. 4C shows the spectral changes observed when the potential corresponding to the process O1 was applied to the solution of [CoIIPc2]. The Q-band at 695 nm increases in intensity with a red shift to 720 nm, while a new band at 450 nm appears as the oxidation process continues. The intensity of the B band decreases with a red shift from 325 nm to 335 nm. These spectral changes occur with clear isosbestic points at 297, 342, 516 and 706 nm in the spectra. A color change from blue to dark blue was also observed during the process. The band at 443 nm and the increase of the Q-band with a red shift are typical of a metal-based oxidation in cobalt Pc complexes. The final spectrum in Fig. 4C is therefore assigned to the [CoIIPc2]/[CoIIIPc2]+ process, confirming the CV assignments. Fig. 4D shows the further oxidation of the [CoIIIPc2]+ species. During this process, the Q-band decreases in intensity without shift and a new band at 809 nm is recorded. The MLCT region between 500 and 600 nm increases slightly in intensity. These spectral changes shows the ring oxidation process and are therefore assigned to the [CoIIIPc2]+/[CoIIIPc1]2+ process [20–25]. 4. Conclusion Non-peripheral 6-hydroxyhexylthio substituents of metal (II) phthalocyanines, (M[Pc(a-SC6H12OH)4](M = Cu(II), Zn(II), Co(II))), exhibited interesting solubility and metal sensing properties. It is important to mention here that the solubility of phthalocyanines is important in terms of high-technological applications. The phthalocyanines synthesized are considerably soluble in polar solvents, such as MeOH, DMSO and DMF. The red shift of the com-

plexes compared to the parent phthalocyanine is due to the electron-donating thioether substituents on the periphery and nonperiphery of the Pc. The stronger electron-releasing 6-hydroxy hexylthio substituents on the non-periphery of the Pc also affect the electrochemical behavior of the complexes, shifting to more negative potentials. This redox feature may be useful for the application of the complexes as electro-catalysts for the reduction and/ or oxidation of many target species, which will be the subject of our future interest. Acknowledgements We thank The Research Fund of Sakarya University and _ TUBITAK (Project no: TBAG-108T094). References [1] X. Li, L.E. Sinks, B. Rybtchinski, M.R. Wasielewski, J. Am. Chem. Soc. 126 (2004) 10810. [2] S.J. Lange, J.W. Sibert, A.G.M. Barrett, B.M. Hoffman, Tetrahedron 56 (2000) 7371. [3] M. Kandaz, S.L.J. Michel, B.M. Hoffman, J. Porphyr. Phthalocya. 7 (2003) 700. [4] N.B. Mc Keown, Phthalocyanine Materials, Cambridge University Press, 1998. _ Yılmaz, Ö. Bekarog˘lu, Polyhedron 19 (2000) 115. [5] M. Kandaz, I. [6] S.L.J. Michel, A.G.M. Barrett, B.M. Hoffman, Inorg. Chem. 42 (2003) 814. [7] N. Preethi, H. Shinohara, H. Nishide, React. Funct. Polym. 66 (2006) 851. [8] S. Lee, A.J.P. White, D.J. Williams, A.G.M. Barrett, B.M. Hoffman, J. Org. Chem. 66 (2001) 461. [9] M.N. Yarasir, M. Kandaz, B.F. Senkal, A. Koca, B. Salih, Polyhedron 26 (2007) 1139. [10] Ö.A. Osmanbasß, A. Koca, M. Kandaz, F. Karaca, Int. J. Hydrogen Energy 33 (13) (2008) 3281. [11] M. Durmusß, T. Nyokong, Inorg. Chem. Commun. 10 (2007) 332. [12] M. Durmus, T. Nyokong, Spectrochim. Acta 69 (2008) 1170. [13] C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: Properties and Applications, vol. 1–4, VCH, Weinheim, 1989. _ Yılmaz, Inorg. Chem. Commun. 10 (2007) 385. [14] S. Arslan, I. [15] M. Kandaz, H.S. Çetin, A. Koca, A.R. Özkaya, Dyes Pigments 74 (2007) 298. [16] A.B.P. Lever, E.R. Milaeva, G. Speier, in: C.C. Leznoff, A.B.P. Lever (Eds.), The Redox Chemistry of Metallophthalocyanines in Solution in Phthalocyanines: Properties and Applications, vol. 3, VCH, New York, 1993, pp. 5–27. [17] M.N. Yarasir, M. Kandaz, B.F. Senkal, A. Koca, B. Salih, Dyes Pigments 77 (2008) 7. [18] P.T. Kissinger, W.R. Heineman, Laboratory Techniques in Electroanalytical Chemistry, second ed., Marcel Dekker, New York, 1996. [19] M.K. Sßener, A. Koca, A. Gül, M.B. Koçak, Polyhedron 26 (2007) 1070. [20] A. Koca, A.R. Özkaya, M. Selçukog˘lu, E. Hamuryudan, Electrochim. Acta 52 (2007) 2683. [21] K. Hesse, D. Schlettwein, J. Electroanal. Chem. 476 (1999) 148. [22] A. Koca, H.A. Dinçer, H. Çerlek, A. Gül, M.B. Koçak, Electrochim. Acta 52 (2006) 1199. [23] B. Agboola, K.I. Ozoemena, T. Nyokong, Electrochim. Acta 51 (2006) 6470. [24] A. Koca, E. Gonca, A. Gül, J. Electroanal. Chem. 612 (2008) 231. [25] A.B.P. Lever, S.R. Pickens, P.C. Minor, S. Licoccia, B.S. Ramaswany, K. Magnell, J. Am. Chem. Soc. 103 (1981) 6800.