Non-aggregated and water soluble amphiphilic silicon phthalocyanines with two axial substituents and their electrochemical properties

Polyhedron 63 (2013) 1–8

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Non-aggregated and water soluble amphiphilic silicon phthalocyanines with two axial substituents and their electrochemical properties Zekeriya Bıyıklıog˘lu ⇑ Department of Chemistry, Faculty of Science, Karadeniz Technical University, 61080 Trabzon, Turkey

a r t i c l e

i n f o

Article history: Received 26 April 2013 Accepted 4 July 2013 Available online 16 July 2013 Keywords: Phthalocyanine Silicon Synthesis Aggregation Quaternization Electrochemistry

a b s t r a c t This paper describes the preparation and electrochemical properties of novel non-aggregated axially disubstituted silicon phthalocyanine complexes and their water soluble derivatives. Silicon phthalocyanine complexes were highly soluble in common organic solvents (CHCl3, CH2Cl2, DMF, DMSO, THF and EtOAc) and their quaternized derivatives were soluble in DMF, DMSO, EtOH, water. The effect of solvents on absorption spectra were studied in various organic solvents. All silicon phthalocyanine complexes were non-aggregated in common organic solvents. The electrochemistry of silicon phthalocyanine complexes was also studied by cyclic voltammetry (CV) and square wave voltammetry (SWV) methods. Cyclic voltammetry revealed two reversible Pc ring-based one-electron reduction couples and two quasi-reversible Pc ring-based one-electron oxidation couples for complexes 3 and 5. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Phthalocyanines and their metal complexes are important commercial compounds owing to their chemical and heat stabilities along various applications. Therefore, in recent years, the synthesis of phthalocyanines attracted attention due to their applications in many field such as liquid crystals [1], solar cell [2], non-linear optics [3], optical data storage [4,5], chemical sensor [6], electrochromic display [7] and photodynamic therapy (PDT) of cancer [8,9]. Many of the applications of phthalocyanine are restrained because of their limited solubility in common organic solvents and water. Also, because of the p–p interaction between planar rings, phthalocyanines usually form aggregates in solution by stacking of phthalocyanine rings. The formation of higher aggregates consequences in lowering the solubility of phthalocyanines. This feature is the disadvantage of application of the phthalocyanine compounds [10]. When conceivable functional groups such as morpholine, polyethylene glycol, fullerene, bulky groups, alkoxy, phenoxycyclotriphosphazenyl, {2-[3-(diethylamino)phenoxy] ethoxy}, crown ether, phenoxy groups at axial substitution of the Pc structure, solubility of phthalocyanines can improve in protic or non-protic solvents [11–19]. In addition, polyethylene oxide derivatives are amphiphilic functional compound which can increases the solubility of phthalocyanines [20]. Phthalocyanines are investigated due to their interesting electrochemical properties [21–24]. The redox properties of phthalocy⇑ Tel.: +90 462 377 36 64; fax: +90 462 325 31 96. E-mail address: [email protected] 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.07.009

anines are related to most of their industrial applications. The application possibilities of phthalocyanine compounds are dependent some factors such as the nature of substituents, type of metal [25]. Along with improving solubility, the nature of axial ligands vigorously influences the spectral and electrochemical properties of the metallophthalocyanines [26].Introducing polyethylene oxide groups as axial ligands into phthalocyanines may have a profound effect on their applications. For these purposes in this study, we have synthesized novel axially disubstituted amphiphilic silicon phthalocyanines, their water soluble derivatives and investigated aggregation and electrochemical properties of these newly synthesized silicon phthalocyanine complexes. 2. Experimental 2.1. Materials Silicon phthalocyanine dichloride 1 [27], was prepared according to the literature. 2-[2-(2-Chloroethoxy)ethoxy]ethanol, 3dimethylaminophenol, 3-diethylaminophenol were purchased from the Aldrich. All reagents and solvents were of reagent grade quality and were obtained from commercial suppliers. All solvents were dried and purified as described by Perrin and Armarego [28]. 2.2. Equipment The IR spectra were recorded on a Perkin Elmer 1600 FT-IR Spectrophotometer, using KBr pellets. 1H and 13C NMR spectra were recorded on a Varian Mercury 200 MHz and Bruker

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2

i N N

O OH

Cl

O

O

O

O

OH

2

OH

N OH

N

i O

O

O

OH

4 Fig. 1. The synthesis of the compounds 2 and 4. (i) Ethanol, NaOH, reflux.

AC-400 MHz spectrometer in CDCl3, DMSO-d6 and chemical shifts were reported (d) relative to Me4Si as internal standard. Mass spectra were measured on a Micromass Quatro LC/ULTIMA LC-MS/MS spectrometer. MALDI-MS of complexes were obtained in dihydroxybenzoic acid as MALDI matrix using nitrogen laser accumulating 50 laser shots using Bruker Microflex LT MALDI-TOF mass spectrometer. Optical spectra in the UV–Vis region were recorded with a Perkin Elmer Lambda 25 spectrophotometer. 2.3. Electrochemical measurements The cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements were carried out with Gamry Interface 1000 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. A Pt wire served as the counter electrode. Saturated calomel electrode (SCE) was employed as the reference electrode and separated from the bulk of the solution by a double bridge. Electrochemical grade TBAP in extra pure DCM was employed as the supporting electrolyte at a concentration of 0.10 mol dm 3. 2.4. Synthesis 2.4.1. 2-(2-{2-[3-(Dimethylamino)phenoxy]ethoxy}ethoxy)ethanol (2) 3-Dimethylaminophenol (6 g, 43.8 mmol) was added to ethanol (50 ml) and nitrogen gas was bubbled through this mixture for 10 min. NaOH (2.2 g, 54.75 mmol) was then added and dissolved by stirring at 50 °C for 1.5 h. 2-[2-(2-Chloroethoxy)ethoxy]ethanol (9.23 g, 54.75 mmol) in 7 ml ethanol was added dropwise to this solution with stirring for 30 min. The reaction mixture was refluxed under nitrogen for 20 h. After the mixture was cooled, the solvent was removed under vacuum, and resulting crude product was dissolved in chloroform (125 ml). The mixture were washed with %10 NaOH and with water. The organic phase was dried over MgSO4, filtered and rotary evaporated. The obtained oily crude product was purified by using column chromatography with Al2O3 as column material and CHCl3 as solvent. Yield: 7.3 g (62%). IR (KBr Tablet), m/cm 1: 3413 (O–H), 3086 (Ar–H), 2916–2874 (Alif. C–H), 1612, 1574, 1503, 1448, 1352, 1324, 1302, 1241, 1125, 1065, 999, 940, 886, 826, 754, 687. 1H NMR (CDCl3), (d:ppm): 7.12 (m, 1H, Ar–H), 6.38–6.31 (m, 3H, Ar–H), 4.10 (t, 2H, CH2–O), 3.84 (t,

2H, CH2–O), 3.70 (m, 4H, CH2–O), 3.59 (m, 4H, CH2-O), 3.24 (s, 1H, OH), 2.92 (s, 6H, CH3). 13C NMR (CDCl3), (d:ppm): 159.96, 152.19, 129.95, 106.21, 102.21, 100.06, 72.87, 70.95, 70.53, 70.03, 67.31, 61.84, 40.86. MS (ESI), (m/z): 270 [M+H]+. 2.4.2. 2-(2-{2-[3-(Diethylamino)phenoxy]ethoxy}ethoxy)ethanol (4) Synthesized similarly to 2 by using 3-diethylaminophenol (6 g, 36.36 mmol). Yield: 4 g (37%). IR (KBr Tablet), m/cm 1: 3433 (O–H), 3089 (Ar–H), 2927–2872 (Alif. C–H), 1612, 1572, 1501, 1453, 1374, 1356, 1285, 1217, 1178, 1141, 1127, 1071, 987, 936, 889, 824, 787, 750, 688. 1H NMR (DMSO-d6), (d:ppm): 6.98 (t, 1H, Ar–H), 6.22 (d, 1H, Ar–H), 6.11 (m, 2H, ArH), 4.62 (t, 1H, OH), 4.00 (t, 2H, CH2–O), 3.68 (t, 2H, CH2–O), 3.48 (m, 4H, CH2–O), 3.41 (m, 4H, CH2–O), 3.28 (q, 4H, CH2), 1.04 (t, 6H, CH3). 13C NMR (DMSO-d6), (d:ppm): 160.45, 149.36, 130.52, 105.36, 101.26, 98.80, 73.06, 70.63, 70.48, 69.79, 67.35, 60.89, 44.37, 13.10. MS (ESI), (m/z): 298 [M+H]+. 2.4.3. Silicon(IV) phthalocyanine (3) A mixture of 2-(2-{2-[3-(dimethylamino)phenoxy]ethoxy}ethoxy)ethanol 2 (178 mg, 0.64 mmol), silicon(IV)phthalocyanine dichloride 1 (200 mg, 0.32 mmol) and NaH (26 mg, 0.64 mmol) in toluene (20 mL) was refluxled for 24 h. Then, the reaction mixture was cooled to room temperature and the solvent was evaporated to dryness under reduced pressure. The solid product was purified by column chromatography which is placed Al2O3 using CHCl3:CH3OH (100:5) as solvent system. Yield: 151 mg (43%). IR (KBr tablet) mmax/cm 1: 3058 (Ar–H), 2928–2864 (Aliph. C–H), 1610, 1572, 1519, 1502, 1427, 1334, 1289, 1234, 1167, 1120, 1078, 998, 910, 826, 734, 686. 1H NMR. (CDCl3), (d:ppm): 9.67 (m, 8H, Pc-Ha), 8.36 (m, 8H, Pc-Hb), 7.17 (m, 2H, Ar–H), 6.39 (m, 6H, Ar–H), 3.91–3.65 (m, 16H, CH2–O), 2.91 (s, 12H, CH3), 1.84 (m, 8H, Si– O–CH2–CH2). 13C NMR (CDCl3), (d:ppm): 159.82, 149.31, 136.04, 131.20, 131.05, 130.90, 123.85, 105.91, 102.03, 99.93, 70.41, 69.40, 68.68, 67.19, 61.76, 54.80, 40.59. UV–Vis (DMF): kmax, nm (log e): 674 (5.30), 643 (4.50), 606 (4.55), 356 (4.84). MALDI-TOFMS: m/z: 1077 [M]+. 2.4.4. Silicon(IV) phthalocyanine (5) Synthesized similarly to 3 from 4. Yield: 74 mg (20%). IR (KBr tablet) mmax/cm 1: 3058 (Ar–H), 2925–2867 (Aliph. C–H), 1610, 1568, 1519, 1500, 1427, 1334, 1289, 1215, 1167, 1122, 1103, 1078, 987, 910, 826, 741, 686. 1H NMR. (CDCl3), (d:ppm): 9.69 (m, 8H, Pc–Ha), 8.35 (m, 8H, Pc–Hb), 7.08 (m, 2H, Ar–H), 6.29 (m,

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3

N O O

O O N N

N

N

N

Si N

N N O

O

3

O

O N

H3C

ii

N H3C

O

O

OH

O

2

Cl N N

N

N

N

Si N

N N

H3C N

Cl H3C

1

O

O

OH

O

4

ii

N O O

O

O N N

N

N

N

Si N

N N O

O

O

5

O N

Fig. 2. The synthesis of the silicon(IV) phthalocyanines 3, 5. (ii) Toluene, NaH, reflux.

6H, Ar–H), 3.78–3.65 (m, 16H, CH2–O), 3.37 (m, 4H, CH2–O), 3.18 (m, 8H, CH2–N), 1.09 (m, 12H, CH3), 1.87 (m, 4H, Si–O–CH2). 13 C NMR (CDCl3), (d:ppm): 160.02, 149.29, 136.03, 130.88, 129.87, 129.72, 123.68, 105.13, 100.70, 99.13, 69.90, 68.66, 67.09, 66.62, 61.81, 54.80, 44.40, 12.63. UV–Vis (DMF): kmax, nm (log e): 674 (5.14), 643 (4.34), 606 (4.40), 355 (4.68). MALDI-TOF-MS: m/ z: 1133 [M]+.

2.4.5. Quaternized silicon(IV) phthalocyanine (3a) Silicon phthalocyanine complex 3 (50 mg, 0.046 mmol) was dissolved in 5 mL chloroform and then 2.5 mL iodomethane was added and this mixture was stirred at room temperature for 5 days. The green precipitate was filtered off, washed with chloroform, acetone, diethyl ether, respectively. Lastly, axially disubstituted water-soluble silicon phthalocyanine 3a was dried in vacuo. Yield:

Z. Bıyıklıog˘lu / Polyhedron 63 (2013) 1–8

4

+

N

N N

N N

N

iii

N

Si N

N

N N

N

N N OR'

OR

3a

3

CH3

CH3 O

.

2 I-

N

Si

N

R=

2

OR'

OR

O

O

N

R'=

CH3

.

O

+

O

O

N

CH3 CH3

+2

OR'

OR N

N N

N

N N

N

N

iii

N

Si

N N

N

N N

N

OR'

OR

5a

5

R= .

O

2 I-

N

Si

CH3

O

O

N

CH3 CH3

R'=

.

O

O

O

+

N

CH3 CH3

Fig. 3. The synthesis of the axially disubstituted water soluble silicon(IV) phthalocyanines 3a, 5a. (iii) CHCl3, CH3-I, room temperature.

Fig. 4. UV–Vis spectrum of 3, 5 in DMF.

30 mg (48%). IR (KBr tablet) mmax/cm 1: 3009 (Ar–H), 2915–2879 (Aliph. C–H), 1607, 1586, 1519, 1490, 1428, 1334, 1291, 1247, 1120, 1054, 943, 741. UV–Vis (DMF): kmax, nm (log e): 674 (5.15), 643 (4.36), 606 (4.42), 355 (4.69). MALDI-TOF-MS: m/z: 838 [M 2I (C15H27NO3)]+.

Fig. 5. UV–Vis spectrum of silicon phthalocyanine 3 in different solvents. (Concentration = 10  10 6 mol dm 3).

2.4.6. Quaternized silicon(IV) phthalocyanine (5a) Synthesized similarly to 3a from 5. Yield: 20 mg (33%). IR (KBr tablet) mmax/cm 1: 3018 (Ar–H), 2926–2865 (Aliph. C–H), 1608, 1520, 1429, 1336, 1291, 1250, 1122, 1078, 911, 736, 691. UV–Vis (DMF): kmax, nm (log e): 672 (4.81), 606 (4.10), 354 (4.40). MALDI-TOF-MS: m/z: 1000 [M 2I (C11H17N)]+.

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Fig. 6. UV–Vis spectrum of silicon phthalocyanine 3 in different solvents. (Concentration = 10  10 6 mol dm 3).

5

Fig. 9. UV–Vis spectrum of water soluble silicon phthalocyanine 3a in DMSO at different concentrations, 12  10 6, 10  10 6, 8  10 6, 6  10 6, 4  10 6, 2  10 6 mol dm 3.

Table 1 Voltammetric data of the silicon phthalocyanine complexes. All voltammetric data were given versus SCE. Complex

Redox processes

E1/2a

DEp (mV)b

Ip,a/Ip,cc

DE1/2d

3

R1 R2 O1 O2 R1 R2 O1 O2

0.72 1.13 0.75 0.98 0.67 1.10 0.74 1.01

74 80 251 155 70 74 248 125

0.84 0.27

1.47

5

a b

Fig. 7. UV–Vis spectrum of water soluble silicon phthalocyanine 3a in different solvents. (Concentration = 10  10 6 mol dm 3).

c d e

e e

0.66 0.27

1.41

e e

E1/2 values ((Epa + Epc)/2) were given versus SCE at 0.100 Vs 1 scan rate. DEp = Epa Epc. Ip,a/Ip,c for reduction, Ip,c/Ip,a for oxidation processes. DE1/2 = E1/2 (first oxidation)-E1/2 (first reduction). DEp could not be determined due to an ill-defined redox wave.

Fig. 8. UV–Vis spectrum of silicon phthalocyanine 3 in DMSO at different concentrations, 12  10 6, 10  10 6, 8  10 6, 6  10 6, 4  10 6, 2  10 6 mol dm 3.

Fig. 10. Cyclic voltammogram of 3 at 0.100 V s

3. Results and discussion 3.1. Synthesis and characterization The preparation of 2-(2-{2-[3-(dimethylamino)phenoxy]ethoxy}ethoxy)ethanol 2, 2-(2-{2-[3-(diethylamino)phenoxy]ethoxy}ethoxy)ethanol 4, silicon phthalocyanine complexes 3, 5 and their water soluble erivatives 3a, 5a are shown in Figs. 1–3, respectively. Firstly, 2-(2-{2-[3-(dimethylamino)phenoxy]ethoxy}eth-

1

in TBAP/DCM.

oxy)ethanol 2 and 2-(2-{2-[3-(diethylamino)phenoxy]ethoxy} ethoxy)ethanol 4 were synthesized by treating 3-dimethylaminophenol, 3-diethylaminophenol with 2-[2-(2-chloroethoxy)ethoxy]ethanol in ethanol at reflux temperature using NaOH as the base, respectively. After that, axially disubstituted silicon phthalocyanines 3, 5 were prepared by heating silicon(IV)phthalocyanine dichloride, 2-(2-{2-[3-(dimethylamino)phenoxy]ethoxy}ethoxy) ethanol, 2-(2-{2-[3-(diethylamino)phenoxy]ethoxy}ethoxy)ethanol in the presence of NaH in toluene at 115 °C for 24 h. Lastly,

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Fig. 11. Square wave voltammogram of 3 at 0.100 V s

Fig. 12. Cyclic voltammogram of 5 at 0.100 V s

1

1

in TBAP/DCM.

in TBAP/DCM.

In the FT-IR spectrum of compound 2 and 4, phenolic OH vibrations disappeared and appeared –CH2–OH peaks at 3413, 3433 cm 1 as expected, respectively. Silicon phthalocyanine complexes 3 and 5 showed two strong C–H and CH2–O bands at (2928–2864 and 1234, 1120 cm 1) for 3, (2925–2867 and 1215, 1122 cm 1) for compound 5, respectively. In the IR spectrum of quaternized silicon phthalocyanine complexes 3a and 5a, no major change was found after quaternization. In the 1H NMR spectrum of compound 2 and 4 appeared new signals at d = 3.24 and 4.62 ppm belonging to OH groups, respectively. In addition, in the 13C NMR spectrum of 2 and 4 appeared the aliphatic carbon atoms at d = 72.87, 70.95, 70.53, 70.03, 67.31, 61.84, 40.86 ppm for compound 2 and 73.06, 70.63, 70.48, 69.79, 67.35, 60.89, 44.37, 13.10 ppm for compound 4. The 1H NMR measurements of silicon phthalocyanine complexes 3 and 5 showed the ecpected total number of aliphatic and aromatic protons for each complex, confirming the purity of complexes as shown in experimental part. In the 13C NMR spectrum of 3 and 5 exhibited the aliphatic carbon atoms at d = 70.41, 69.40, 68.68, 67.19, 61.76, 54.80, 40.59 ppm for compound 3 and 69.90, 68.66, 67.09, 66.62, 61.81, 54.80, 44.40, 12.63 ppm for compound 5, respectively confirming formation of the compounds 3 and 5. Compound 2 and 4 showed the expected molecular ion peaks at m/z = 270 [M+H]+ and 298 [M+H]+, respectively also supports the recommended structures. The proof of the structure of silicon phthalocyanine complexes 3 and 5 and their water soluble derivatives 3a and 5a was given by MALDI-TOF mass spectrometry where molecular ion peaks at m/z = 1077 [M]+ and 1133 [M]+ respectively. The molecular ion peaks of the quaternized silicon phthalocyanine complexes 3a and 5a were observed at 838 [M 2I (C15H27NO3)]+ and 1000 [M 2I (C11H17N)]+, respectively. In the UV–Vis spectrum of the synthesized silicon phthalocyanine complexes 3 and 5 showed monomeric behavior in DMF evidenced by a single (narrow) Q-bands (674, 643, 606 nm) for compound 3, (674, 643, 606 nm) for 5, respectively that confirm the non-aggregation. B band absorptions of the silicon phthalocyanine complexes 3 and 5 in DMF were observed at 356 nm for compound 3, 355 nm for compound 5, respectively (Fig. 4). 3.2. Aggregation studies

Fig. 13. Square wave voltammogram of 5 at 0.100 V s

1

in TBAP/DCM.

quaternized silicon phthalocyanine complexes 3a and 5a were prepared from the reaction of corresponding silicon phthalocyanine complexes 3 and 5 with iodomethane as quaternization agent in chloroform. After reaction with iodomethane, the quaternized silicon phthalocyanine complexes 3a and 5a are very soluble in water. All new compounds were characterized by using UV–Vis, IR, 1H NMR, 13C NMR, MS spectroscopic data, all of which were coherent with the recommended structures.

Generally, aggregation is highly depends on concenctration, temperature, nature of the substituents, nature of solvents and complexed metal ions [29]. In this work, the aggregation behavior of the silicon phthalocyanine complexes 3 and 5 were investigated in different solvents such as chloroform, dichloromethane, DMF, DMSO, THF and ethyl acetate (Figs. 5 and 6 as an example for complex 3). Also, aggregation behavior of the water soluble silicon phthalocyanine complexes 3a and 5a were investigated in different solvents such as DMF, DMSO, EtOH, water (Fig. 7 as an example for complex 3a). Silicon phthalocyanine complexes 3 and 5 did not show any aggregation in chloroform, dichloromethane, DMF, DMSO, THF, ethyl acetate, water soluble complexes 3a and 5a did not show any aggregation in DMF, DMSO, EtOH and water. Because, the strong single Q-band peak is characteristic of monomeric form of silicon phthalocyanine complexes. Moreover, silicon phthalocyanine complexes 3 and 5 and their water soluble derivatives 3a and 5a were also examined by the spectra monitored at different concentrations in DMSO. In DMSO, as the concentration was increased, the intensity of absorbtion of the Q band also increased and there were no new bands (normally blue shifted) due to the aggregated species for all phthalocyanines (Fig. 8 as an example for complex 3, Fig. 9 as an example for complex 3a). Therefore, the complexes 3, 5, 3a and 5a did not show aggregation in DMSO at different concentrations. Beer–Lambert law was obeyed for all of the compounds in the concentrations ranging from 12  10 6 to 2  10 6 mol dm 3.

Z. Bıyıklıog˘lu / Polyhedron 63 (2013) 1–8

Fig. 14. Cyclic voltammogram of silicon phthalocyanine complex 3 at various scan rates (ranging from 50 to 1000 mV s 1) on a Pt working electrode in DCM/TBAP.

7

cals, occur only at the ligand in some metallophthalocyanines involving a redox-inactive metal center, while they occur both at the metal center and at the phthalocyanine ring in those with redox-active metal centers [30–32]. Because the central Si(IV) metal is redox inactive, all the couples of 3 and 5 are detected exactly to the phthalocyanine ring. Cyclic and square wave voltammetric studies indicated that silicon phthalocyanine complexes 3 and 5 have similar well-defined ring based two redox couples and two oxidations marked R1, R2, O1 and O2. Axially disubstituted silicon phthalocyanine complex 3 represents two reversible Pc ring-based one-electron reduction couples with respect to DEp values, which are assigned to [SiIVPc 2]+2/[SiIVPc 3]+1 at 0.72 V (DEp = 74 mV and Ip,a/Ip,c = 0.84 at 0.100 mVs 1 scan rate) and [SiIVPc 3]+1/[SiIVPc 4] at 1.13 V (DEp = 80 mV and Ip,a/Ip,c = 0.27 at 0.100 mVs 1 scan rate) and two quasi-reversible Pc ring-based one-electron oxidation couple assigned to [SiIVPc 2]+2/[SiIVPc ]+3 at 0.75 V (DEp = 251 mV at 0.100 mV s 1 scan rate) and [SiIVPc 1]+3/[SiIVPc]+4 at 0.98 V (DEp = 155 mV at 0.100 mV s 1 scan rate). Similarly, silicon phthalocyanine complex 5 gives very close results with the silicon phthalocyanine complex 3. The peak currents for complex 3 and 5 increased linearly with the square root of the scan rates for scan rates ranging from 50 to 1000 mV s 1 (Fig. 14 for complex 3, Fig. 15 for complex 5), indicating purely diffusion-controlled behavior [33–35]. Despite DEp values of the first reduction couple is in reversible range, the values of Ipa/Ipc are less than unity at all scan rates suggesting existence of a fast irreversible chemical reaction succeeding the second reduction reaction [36]. 4. Conclusion

Fig. 15. Cyclic voltammogram of silicon phthalocyanine complex 5 at various scan rates (ranging from 50 to 1000 mV s 1) on a Pt working electrode in DCM/TBAP.

3.3. Electrochemical measurements The electrochemical behaviors of the axially disubstituted silicon phthalocyanine complexes 3 and 5 were studied by using cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements in dichloromethane (DCM), containing 0.1 mol dm 3 tetrabutylammonium perchlorate (TBAP) on a Pt electrode. Table 1 lists the values of the couples recorded and the estimated electrochemical parameters, which includes the half-wave potentials (E1/2), the ratio of anodic to cathodic peak currents (Ipa/Ipc), peak to peak potential separations (DEp) and the difference between the first reduction and oxidation processes (DE1/ 2). DE1/2 express the HOMO–LUMO gap for silicon phthalocyanines. Figs. 10 and 11 illustrate the cyclic and square wave voltammogram of the axially disubstituted silicon phthalocyanine 3 in DCM containing TBAP. Cyclic voltammogram of silicon phthalocyanine 3 gives two one-electron reduction processes marked as R1 at 0.72 V, R2 at 1.13 V and two one-electron oxidation processes marked as O1 at 0.75 V, O2 at 0.98 V versus SCE at 0.100 V s 1 scan rate. Figs. 12 and 13 illustrate the cyclic and square wave voltammogram of the axially disubstituted silicon phthalocyanine complex 5 in DCM containing TBAP. Similarly, silicon phthalocyanine complex 5 gives very close voltammetric responses with silicon phthalocyanine complex 3 as seen in Table 1. Reduction and oxidation redox processes, generally associated with the transfer of one electron and therefore the formation of anionic and cationic radi-

In summary, in this work synthesis, spectral characterization, aggreagation and electrochemical properties of novel axially disubstituted silicon phthalocyanine complexes and their water soluble derivatives were presented. The silicon phthalocyanine complexes are easily soluble in common organic solvents. Aggregation behavior of silicon phthalocyanine in different solvents were studied by means of UV–Vis absorption spectroscopy. Axially disubstituted silicon phthalocyanines did not show any aggregation in studied solvents. Owing to the non-aggregating in water, silicon phthalocyanine complexes 3a and 5a can be used as potential PDT agents. Also, cyclic and square wave voltammetric studies show that axially disubstituted silicon phthalocyanine complexes 3 and 5 have one electron reversible/quasi-reversible redox processes, which are the main requirement for the technological usage of these compounds. Acknowledgement This study was supported by The Scientific & Technological Re_ Project No. 111T963). search Council of Turkey (TÜBITAK, References [1] C. Piechocki, J. Simon, A. Skoulios, D. Guillon, P. Weber, J. Am. Chem. Soc. 104 (1982) 5245. [2] M.K.R. Fischer, I. Lopez-Duarte, M.M. Wienk, M.V. Martinez-Diaz, R.A.J. Janssen, P. Bauerle, T. Torres, J. Am. Chem. Soc. 131 (2009) 8669. [3] A. Grund, A. Kaltbeitzel, A. Mathy, R. Schwarz, C. Bubeck, P. Vernmehren, M. Hanack, J. Phys. Chem. 96 (1992) 7450. [4] M. Emmelius, G. Pawlowski, H.W. Vollmann, Angew. Chem., Int. Ed. 28 (1989) 1445. [5] L. Tao, G. Fuxi, Appl. Opt. 33 (1994) 3360. [6] A.W. Snow, W.R. Barger, M. Klusty, H. Wohltjen, N.L. Jarvis, Langmuir 2 (1986) 513. [7] M. Rodriguez-Mendez, R. Aroca, J.A. DeSaja, Chem. Mater. 5 (1993) 933. [8] A.M. Master, M.E. Rodriguez, M.E. Kenney, N.L. Oleinick, A.S. Gupta, J. Pharm. Sci. 99 (2010) 2386.

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