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Dyes and Pigments 99 (2013) 613e619

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Dyes and Pigments

journal homepage: www.elsevier .com/locate/dyepig

Synthesis, characterization, electrochemical andspectroelectrochemical properties of peripherally tetra-substitutedmetal-free and metallophthalocyanines

Ayse Aktas a, _Irfan Acar b, Atıf Koca c, Zekeriya Bıyıklıo�glu a, Halit Kantekin a,*

aDepartment of Chemistry, Faculty of Science, Karadeniz Technical University, 61080 Trabzon, TurkeybDepartment of Energy Systems Engineering, Faculty of Technology, Karadeniz Technical University, 61830 Trabzon, TurkeycDepartment of Chemical Engineering, Engineering Faculty, Marmara University, Göztepe, 34722 Istanbul, Turkey

a r t i c l e i n f o

Article history:Received 7 May 2013Received in revised form26 June 2013Accepted 29 June 2013Available online 10 July 2013

Keywords:MetallophthalocyanineSynthesisMicrowaveElectrochemistrySpectroelectrochemistryElectropolymerization

* Corresponding author. Tel.: þ90 462 377 25 89; fE-mail address: halit@ktu.edu.tr (H. Kantekin).

0143-7208/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.dyepig.2013.06.033

a b s t r a c t

In this study, the synthesis, electrochemical and spectroelectrochemical properties of peripherally2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethanol substituted novel metal-free 4, Zn(II) 5,Ni(II) 6, Co(II) 7 and Cu(II) 8 phthalocyanine derivatives are reported. These new compounds have beencharacterized by using UVeVis, IR, 1H NMR, 13C-NMR (just for phthalonitrile derivative) and MS spec-troscopic data. Electrochemical and spectroelectrochemical measurements exhibit that while CoPc givesa metal-based reduction process in addition to the ring-based reduction process, all the other complexesgive common ring reduction reaction of MPcs which have redox inactive metal center. 2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethanol groups which substituted on the periphery of thecomplexes provides electropolymerization of the complexes during the anodic potential scans. Type ofthe metal center of the complexes, which was used potential windows and the cycle numbers affect thecharacter of the polymerization processes during the cyclic voltammetry measurements.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Phthalocyanines (Pcs) have remarkable physical and chemicalproperties [1]. For many years, their wide application areas such asin the construction of molecular devices have attracted increasinginterest [2]. Because of their powerful delocalized 18-p electronaromatic molecules which show strong absorption in the visibleregion, they are extensively used as dyestuffs for textiles and inks[3]. Besides, phthalocyanines can be used electrochromic displaydevices, oxidation catalysts, data storage, chemical sensors, liquidcrystals, LangmuireeBlodgett films, photovoltaic solar cells, non-linear optics application, gas sensors, light emitting diodes andphotodynamic therapy (PDT) which is an alternative method in thetreatment of the cancer [4e11].

Since 1980, microwave (MW) irradiation can be used for syn-thesizing phthalocyanines as an alternative method [12]. Microwave

ax: þ90 462 325 31 96.

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assisted synthesis have many advantages such as reducing chemicalreactions times and side reactions also increasing the yieldunlike classic method does [13]. In this paper, we describe the syn-thesis and characterization of metallophthalocyanines (MPc;M ¼ Zn(II), Ni(II), Co(II)) and Cu(II) substituted with 2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethanol groups by mi-crowave irradiation.

It is well known that, phthalocyanine complexes show excellentelectrochromic properties both in solution and as films [14e16]. Inaddition, MPcs found area in high tech applications due to theirhigh chemical and thermal stability, designed flexibility, variedcoordination properties, diversed substitutional alternatives andinteresting electrochemical properties [17e19]. Their electro-chemical properties can be arranged by incorporating desiredmetal and/or substituents. Therefore electrochemical behavior of anewly synthesized complexes should be analyzed in detail todecide its possible application in various electrochemical technol-ogies, thus we have investigated the electrochemical and spec-troelectrochemical properties of these newly synthesized MPccomplexes.

A. Aktas et al. / Dyes and Pigments 99 (2013) 613e619614

2. Experimental

2.1. Synthesis

2.1.1. Synthesis of 4-[2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethoxy] phthalonitrile (3)

4-Nitrophthalonitrile 2 (0.74 g, 4.3 � 10�3 mol) was dissolved in10 ml of dry DMF under N2 atmosphere, and 2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethanol 1 (1 g, 4.3 � 10�3 mol) wasadded to reaction mixture. After being stirred for 30 min at 60 �C,finely ground anhydrous K2CO3 (1.78 g, 10.5 � 10�3 mol) was addedportionwisewithin 2 h. The reactionmixturewas stirred under N2 at60 �C for 4 days. Thereafter, the reaction mixture was poured intoice-water and stirred at room temperature for 3 h to yield a crudeproduct. The mixture was filtered and dried in vacuum over P2O5 for4 h and recrystallized from ethanol to give dark yellow crystallinepowder. Yield: 0.9 g (56%). mp: 114e117 �C. IR (KBr pellet), nmax/cm�1: 3044 (AreH), 2966e2872 (Aliph. CeH), 2231 (C^N), 1600e1564 (CeO),1504,1423,1364,1321,1253,1217, 1199,1151,1098,1089,1017, 963, 800, 756, 596. 1HNMR. (CDCl3), (d:ppm): 7.69 (d, H, AreH),7.27e7.08 (m, 3H, AreH), 6.59 (d, 1H, AreH), 6.40 (s, 1H, AreH), 4.19(t, 4H, CH2eO), 3.88 (m, 2H, CH2eN), 2.83 (m, -CH-), 2.30 (s, 3H,-CH3), 1.83e1.74 (m, 2H eCH2), 1.59e1.20 (m, 9H -CH3). 13C-NMR.(CDCl3), (d:ppm): 162.14, 144.32, 136.83, 135.49, 126.51, 126.31,120.02, 119.48, 117.75, 117.67, 115.93(C^N), 115.44(C^N), 111.97,107.58, 67.35, 54.86, 47.18, 43.75, 29.83, 27.32, 25.07, 22.05, 20.25. MS(ESI), (m/z): 359 [M]þ.

2.1.2. Synthesis of metal-free phthalocyanine (4)A mixture of phthalonitrile 3 (0.2 g, 0.56 � 10�3 mol) and cat-

alytic amount of 1.8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 2 mlof dry n-pentanol was heated and stirred at 160 �C in a sealed glasstube for 16 h under N2. After being cooled to room temperature thegreen crude product was precipitated with ethanol, filtered andwashed first with ethanol then diethyl ether and then dried invacuo. Finally, pure metal-free phthalocyanine was obtainedby column chromatography which is placed silica gel usingCHCl3:CH3OH (10:1) as solvent system. Yield: 0.098 g (49%). mp:>300 �C. IR (KBr tablet) nmax/cm�1: 3292 (NeH), 3040 (AreH),2963e2855 (Aliph. CeH), 1729, 1610, 1571, 1504, 1467, 1426, 1342,1324, 1240, 1168, 1116, 1098, 1016, 797, 756, 596. 1H NMR. (CDCl3),(d:ppm): 8.97 (4H, AreH), 8.33 (4H, AreH), 7.56 (4H, AreH), 7.28(12H, AreH), 6. 91 (4H, AreH), 5.66 (4H, AreH), 4.63 (8H, CH2eO),3.94 (8H, CH2eN), 3.04 (4H, -CH-), 2.49 (12H, -CH3), 1.60 (8H, -CH3),1.44 (28H, -CH3). UVeVis (THF): lmax, nm (log 3): 703 (4.90), 666(4.85), 643 (4.45), 605 (4.24), 383 (4.37), 343 (4.67), 290 (4.5).MALDI-TOF-MS, (m/z): Calculated: 1439.84; Found: 1439.24 [M]þ.

2.1.3. Synthesis of zinc(II) phthalocyanine (5)A mixture of phthalonitrile 3 (0.15 g, 0.42 � 10�3 mol), anhy-

drous metal salts Zn(CH3COO)2 (0.038 g, 0.21 � 10�3 mol), and dryDMAE (1 ml) was irradiated in a microwave oven at 175 �C, 350 Wfor 4 min. After being cooled to room temperature, the reactionmixture was precipitated by the addition of ethanol and greenprecipitate was filtered off. The obtained green product was filteredoff, washed with ethanol and diethyl ether and then dried in vacuo.Purification of the solid products were accomplished by columnchromatography which is placed silica gel using CHCl3:CH3OH (5:1)as solvent system. Yield: 0.058 g (36%). mp:>300 �C. IR (KBr tablet)nmax/cm�1: 3040 (AreH), 2960-2856 (Aliph. CeH), 1727,1664,1609,1463, 1448, 1364, 1336, 1283, 1238, 1198, 1170, 1090, 1053, 962, 838,796, 747. 1H NMR. (CDCl3), (d:ppm): 8. 70 (4H, AreH), 8.11 (4H, AreH), 7.73 (4H, AreH), 7.27 (12H, AreH), 6.83 (4H, AreH), 6.61 (4H,AreH), 4.53 (8H, CH2eO), 3.83 (8H, CH2eN), 3.00 (4H, -CH-), 2.44(12H, -CH3), 1.66 (8H, -CH3), 1.39 (28H, -CH3). UVeVis (THF): lmax,

nm (log 3): 678 (4.94), 612 (4.32), 349 (4.79), 308 (4.67). MALDI-TOF-MS, (m/z): Calculated: 1501,37; Found: 1502.75 [M þ H]þ.

2.1.4. Synthesis of nickel(II) phthalocyanine (6)Synthesized similarly from 5 to 3 by using anhydrous NiCl2.

Yield: 0.056 g (27%). mp: >300 �C. IR (KBr tablet) nmax/cm�1: 3042(AreH), 2959e2850 (Aliph. CeH), 1728, 1610, 1504, 1464, 1418,1383, 1343, 1271, 1241, 1169, 1125, 1097, 1088, 960, 796, 750, 595. 1HNMR. (CDCl3), (d:ppm): 7.27 (12H, AreH), 6.89 (4H, AreH), 6.67(4H, AreH), 4.64 (8H, CH2eO), 4.00 (8H, CH2eN), 3.05 (4H, -CH-),2.51(12H, -CH3), 1.58-1.26 (48H, -CH3).UVeVis (THF): lmax, nm(log 3): 673 (4.91), 607 (4.31), 382 (4.18), 328 (4.39). MALDI-TOF-MS, (m/z): Calculated: 1494.7; Found: 1495.86 [M þ H]þ.

2.1.5. Synthesis of cobalt(II) phthalocyanine (7)Synthesized similarly from 5 to 3 by using anhydrous CoCl2.

Yield: 0.085 g (40%). mp: >300 �C. IR (KBr tablet) nmax/cm�1: 3033(AreH), 2961e2870 (Aliph. CeH), 1726, 1609, 1572, 1504, 1463,1418, 1383, 1342, 1281, 1241, 1170, 1098, 1065, 960, 838, 752, 665.UVeVis (THF): lmax, nm (log 3): 665 (4.77), 605 (4.24), 306 (4.76).MALDI-TOF-MS, (m/z): Calculated: 1494.93; Found: 1495.09[M þ H]þ.

2.1.6. Synthesis of copper(II) phthalocyanine (8)Synthesized similarly from 5 to 3 by using anhydrous CuCl2.

Yield: 0.024 g (13%). mp: >300 �C. IR (KBr tablet) nmax/cm�1: 3035(AreH), 2969e2854 (Aliph. CeH), 1728, 1607, 1504, 1486, 1460,1364, 1340, 1284, 1242, 1195, 1123, 1017, 837, 797, 756, 665, 595.UVeVis (THF): lmax, nm (log 3): 678 (4.80), 611 (4.32), 337 (4.87).MALDI-TOF-MS, (m/z): Calculated: 1499.55; Found: 1500.42[M þ H]þ.

3. Results and discussion

3.1. Syntheses and characterization

Starting from 2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethanol 1 and 4-nitrophthalonitrile 2, the general syn-thetic route for the synthesis of new metal-free and metal-lophthalocyanines are given in Figs. 1 and 2. The synthesis ofcompound 3 is based on the reaction of 2-(2,2,4,7-tetramethyl-3,4-dihydroquinolin-1(2H)-yl)ethanol 1 with 4-nitrophthalonitrile 2(in dry DMF and in the presence of dry K2CO3 as base, at 55 �C in96 h). Cyclotetramerization of the phthalonitrile derivative 3 to themetal-free phthalocyanine 4 was accomplished in n-pentanol inthe presence of a few drops of 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU) as a strong base at 160 �C in sealed tube. The metal-lophthalocyanines 5e8were obtained by the anhydrous metal salts[Zn(CH3COO)2, NiCl2, CoCl2 and CuCl2] in 2-(dimethylamino)ethanol by microwave irradiation. The structures of the targetcompounds were confirmed using UVeVis, IR, 1H NMR, 13C NMR(just for phthalonitrile derivative) and MS spectral data.

In the IR spectra of compound 3 was clearly confirmed by thedisappearance of the OH and appearance of the new vibration C^Nband at 2231 cm�1. In the 1H NMR spectrum of 3, OH group ofcompound 1 disappeared as being expected. 1H NMR spectrum of 3showed new signals at d ¼ 7.24e7.09 (m, 3H, AreH) belonging toaromatic protons. In the 13C NMR spectrum of 3 indicated thepresence of nitrile carbon atoms in 3 at d¼ 115. 93 and 115. 44 ppm.TheMS spectrum of compound 3, which shows a peak at m/z¼ 359[M]þ support the proposed formula for this compound.

After transformation of the dinitrile 3 to the phthalocyanines,the sharp C^N vibration around 2231 cm-1 disappeared. IR spectraof phthalocyanines 4e8 are very similar, with the exception of themetal-free 4which shows an NH stretching band peak at 3292 cm-1

N

CH3

CH3

CH3

H3C

HO

O2N

CN

CN

N

CH3

CH3

CH3

H3C

O

NC

NC

OO

O

N

N

N

HN

N

NNH

N

N

CH3

H3C CH3

H3C

N

H3CCH3

CH3

CH3

NH3C

CH3H3C

CH3

ON

CH3

H3C CH3

H3C

1 2

3

4

dry K2CO3

dry DMF

DBU

n-pentanol160 oC

50oC

Fig. 1. The synthesis route of the metal-free phthalocyanine 4.

A. Aktas et al. / Dyes and Pigments 99 (2013) 613e619 615

due to the inner core. The 1H NMR spectra of 4 indicated charac-teristic protons between 8.97 and 1.44 ppm. But, the NH protons ofmetal-free phthalocyanine 4 could not be observed owing to theprobable strong aggregation of the molecules [20,21]. In the massspectra of compound 4, the presence of the characteristicmolecularion peak at m/z ¼ 1439.24 [M]þ confirmed the proposed structure.

In the IR spectra of the metallophthalocyanines 5e8 cyclo-tetramerization of 3 was confirmed by the disappearance of thesharp C^N stretching vibration at 2231 cm�1. The IR spectra ofZnPc, NiPc, CoPc and CuPc are also very similar to that of the pre-cursor H2Pc. The 1H NMR spectra of compound 7 and 8 could not bedetermined because of the paramagnetic nature. The 1H NMRspectra of the compounds 5 and 6 were almost same to those ofH2Pc 4. In the MALDI-mass spectrum of Zn, Ni, Co, Cu phthalocy-anines, the presence of molecular ion peaks at m/z ¼ 1502.75[M þ H]þ for Zn(II), 1495.86 [M þ H]þ for Ni (II), 1495.09 [M þ H]þ

for Co(II) and 1500.43 [M þ H]þ for Cu(II) respectively, confirmedthe proposed structures.

The UVeVis spectra of the phthalocyanine complexes whichexhibit typical electronic spectra with two strong absorption re-gions, one of them is in the visible region at 600e700 nm (Q band)

and the other one is in the UV region at about 300e500 nm(B band), both correlate to p/ p* transitions [22e24]. The groundstate electronic spectra of the compounds showed characteristicabsorptions in the Q band region at 703/666 nm for compound 4,678 nm for compound 5, 673 for compound 6, 665 nm for com-pound 7, 678 nm for compound 8 in THF. B band absorptions ofthe metal-free and metallophthalocyanines 5e8 were observedat (383, 290), (349, 308), (382, 328), 306 nm, 337 respectively(Figs. 3 and 4).

3.2. Voltammetric measurements

The electrochemical analyses of the MPc complexes were per-formed in DCM/TBAP electrolyte system on a Pt working electrode.The results of these analyses are tabulated in Table 1. The assign-ments of the redox couples and estimated electrochemical pa-rameters including the half-wave peak potentials (E1/2), ratio ofanodic to cathodic peak currents (Ip,a/Ip,c), peak to peak potentialseparations (DEp), and difference between the first oxidation andreduction processes (DE1/2) are listed for the comparison of thecomplexes. As shown in Table 1, H2Pc, NiPc, ZnPc and CuPc illustrate

OO

O

N

N

N

N

N

NN

N

M

N

CH3

H3CCH3

H3C

N

H3CCH3

CH3

CH3

NH3C

CH3H3C

CH3

ON

CH3

H3C CH3

H3C

N

CH3

H3C

H3C

CH3

O

CNNC

MW

175 oC 350 Watt

DMAE

Compound 5 6 7 8

M Zn Ni Co Cu

Fig. 2. The synthesis route of metallophthalocyanines 5, 6, 7 and 8.

A. Aktas et al. / Dyes and Pigments 99 (2013) 613e619616

very similar voltammetric responses, because all of these com-plexes have redox inactive metal centers and gives only Pc ring-based redox processes. All of these complexes give two reversiblereduction processes at the cathodic potentials and electro-polymerized on the working electrode during the anodic potentialscans. The only differences are the small potential differences dueto the different effective nuclear charge of the metal center of thesecomplexes and the polymerization mechanism. Fig. 5 representsthe CV and SWV responses of NiPc as a representative of H2Pc,NiPc, ZnPc and CuPc complexes. Within the potential window ofDCM/TBAP electrolyte system, NiPc illustrates two diffusioncontrolled and quasi-reversible reductions processes. The couples,R1 at �0.94 V (DEp ¼ 100 mV and Ip,a/Ip,c ¼ 0.96) and R2at �1.29 V(DEp ¼ 85 mV and Ip,a/Ip,c ¼ 0.93), are resolved well. Thereduction couples of NiPc are electrochemically quasi-reversible atall scan rates with respect to DEp and Ip,a/Ip,c values. These processes

Fig. 3. UVeVis absorption spectra changes of compounds 4 and 5 in THF at1 � 10�5 mol dm�3.

are chemically reversible and diffusion controlled with respect to[Ipan1/2] and Ip,a/Ip,c values [25]. These voltammetric analyses aresupported with the CV measurements with different vertex po-tentials given in Fig. 5a. As shown in this figure, altering the vertexpotential does not affect the character of the redox processes.Fig. 5b illustrates the repetitive CV responses of NiPc during theanodic potential scans. As shown in this figure, during the firstanodic potential scan, a huge anodic peak is recorded at 1.16 V andits cathodic couple is recorded at 0.31 V. During the repetitive CVscan these waves increase in current intensity with potential shift.While DEp value is 0.85 V for the first scan this value increase to1.50 V for the 20 cycle. The peak current of the electro-polymerization waves increases continuously with the consecutiveCV cycles. Changing the potential window of the CV cycles altersthe polymerization process completely. While only an anodicirreversible electropolymerization couple is recorded during the

Fig. 4. UVeVis absorption spectra changes of compounds 6, 7 and 8 in THF at1 � 10�5 mol dm�3.

Fig. 6. Repetitive CVs of NiPc recorded with in the both anodic and cathodic potentialwindows of DCM/TBAP at 0.100 V s�1 scan rate on a Pt working electrode.

Table 1Voltammetric data of the complexes with the related MPcs. All voltammetric datawere given versus SCE.

Complex Electropolymerization peaks MII/MI Ring reductions

H2Pc aE1/2 0.73 0.63 0.55 e �0.81 �1.16bDEp (mV) 80d 100d e e 62 65cIp,a/Ip,c e e e e 0.97 0.85

NiPc aE1/2 e 0.80 0.56 e �0.94 �1.29bDEp (mV) e 375d 140d e 100 95cIp,a/Ip,c e e e e 0.98 0.89

ZnPc aE1/2 e 0.77 0.54 e �0.95 �1.30bDEp (mV) e 250d 110d e 105 95cIp,a/Ip,c e e e e 0.97 0.94

CuPc aE1/2 e 0.77 0.62 e �0.85 �1.22bDEp (mV) e 110d 88d e 85 110cIp,a/Ip,c e e e e 0.88 0.78

CoPc aE1/2 e 0.77 0.63 �0.37 �1.50 ebDEp (mV) e 100e 60e 68 62 ecIp,a/Ip,c e e e 0.87 0.91 e

a E1/2 values ((Epa þ Epc)/2) were given versus SCE and Fc/Fcþ (in parenthesis) at0.100 V s�1 scan rate.

b DEp ¼ Epa � Epc.c Ip,a/Ip,c for reduction, Ip,c/Ip,a for oxidation processes.d Recorded by SWV.e DEp values derived from the first CV cycle.

A. Aktas et al. / Dyes and Pigments 99 (2013) 613e619 617

anodic potential scans. The number of peaks, their reversibility andpeak currents change completely, when both of the anodic andcathodic potentials are scanned. Fig. 6 represents the repetitive CVresponses of NiPc between�2.00 andþ1.50 V. During the first scanfrom 0.00 V to�2.0 V, NiPc gives two reduction peaks, R1 at�1.03 Vand R2 at �1.37 V. During the reverse scan from �2.0 to 1.50 V,anodic couples of R1 and R2 are recorded at �0.86 V at �1.24 Vrespectively at the cathodic side of the voltammograms. On theanodic side, a huge anodic wave Pa1, is recorded at 1.00 V and itscathodic couple, Pc1, is recorded at 0.62 V during the potential scan

Fig. 5. (a) CVs of NiPc at various scan rates during the cathodic potential scan (b)Repetitive CVs of NiPc during the anodic potential scan at 0.100 V s�1 scan rate on a Ptworking electrode in DCM/TBAP.

from 1.50 to 0.0 V. In addition, a second cathodic wave, Pc2, isrecorded at 0.50 V. During the consecutive potential scans, whilethe R1 and R2 disappeared completely a new reduction peak, Pc3, isrecorded at �1.41 V, which shifts to negative potentials with de-creases in current intensity and finally disappears. When Pc3peak isrecorded, a newwave Pa2 starts to increase at 0.61 V. However, whenthe Pc3 wave disappears, the Pa2 wave decreases in intensity. After 6CV cycle, all waves start to decrease in current intensity due to thefinalizing of the electropolymerization. In summary, when negativepotentials are scanned with positive potentials, more redox pro-cesses are observed and the electropolymerization process is morereversible. However, the electropolymerization process finishesafter the 6 CV cycle. Similar polymerization processes were alsorecorded with H2Pc, ZnPc and CuPc complexes.

Fig. 7 shows the CV and SWV responses of CoPc in DCM/TBAPelectrolyte system. CoPc displays two well-resolved reversible anddiffusion controlled reduction processes. SWVs clearly show thechemical and electrochemical reversibility of the redox processes

Fig. 7. (a) CVs of CoPc at various scan rates during the cathodic potential scan. (b)SWVs of CoPc at various scan rates during the cathodic potential scan.

A. Aktas et al. / Dyes and Pigments 99 (2013) 613e619618

(Fig. 7b). In practical applications, DEp of a couple is compared withthat of universal indicator ferrocene/ferrocenium couple to decidethe reversibility of a couple. In our system, DEps were changed from60 to 110 mV for ferrocene with increasing scan rates from 0.010 to1.00 V s�1. When compared with the responses of ferrocene, DEpvalues of both reduction processes of CoPc are in electrochemicalreversibility range. The effect of coupled chemical reactions to theelectron transfer reactions is illustrated with Ip,a/Ip,c ratio change asa function of the scan rate. Both reduction processes that arerecorded with CoPc are purely diffusion that are controlled withrespect to unit Ip,a/Ip,c ratio at all scan rates. Moreover reversibilityof these couples can be concluded with respect to symmetry andpeak current ratios of the waves that are recorded during the for-ward and reverse SWV scans (Fig. 7b) [25].

Fig. 8 illustrates the repetitive CV responses of CoPc in DCM/TBAP. Within the electrochemical window of DCM/TBAP in CVmeasurements between 1.60 and �1.80 V, CoPc undergoes tworeversible one-electron reduction processes during the firstcathodic cycle (Fig. 8). However CoPc gives two huge redox couplesat 0.63 V ðPa1=Pc1Þ and 0.77 V ðPa2=Pc2Þ due to the polymerization ofthe complex on the working electrode. In addition to the anodicpolymerization couples, a new small reduction peak increasesat �1.36 V. All peaks due to the polymerization increases in currentintensity as a function of repetitive CV scan until 10. CV cycle. Whenthey are compared with NiPc, wave of the polymers of CoPc aremore reversible and increases continuously in current intensity as afunction of CV scan until 10. CV cycle.

3.3. Spectroelectrochemical measurements

Spectroelectrochemical studies were employed to confirm theassignments of the redox couples that were recorded in the CVs andSWVs of the complexes. H2Pc, NiPc, ZnPc and CuPc complexes haveredox inactive metal center, thus UVeVis spectral changes whichwere characteristic ring-based reduction reactions were recordedduring the in-situ spectroelectrochemical measurements. CoPc hasredox active metal center, thus in-situ spectroelectrochemicalmeasurements were performed for the assignments of the redoxcouples.

Fig. 9 represents in situ UVeVis spectral changes and in siturecorded chromaticity diagram of CoPc in DCM/TBAP during theelectron transfer processes. During the first reduction process,while the Q band shifts from 677 nm to 708 nm, a new band en-hances at 475 nm. These spectral changes characterize the forma-tion of [CoIPc�2]1� species under the applied potential at �0.50 V(Fig. 9a) [26e32]. This process did not give clear isosbestic points.

Fig. 8. Repetitive CVs of CoPc recorded with in the both anodic and cathodic potentialwindows of DCM/TBAP at 0.100 V s�1 scan rate on a Pt working electrode.

Fig. 9. In-situ UVeVis spectral changes of CoPc in DCM. a) Eapp ¼ �0.6 V b)Eapp ¼ �1.70 V c) Chromaticity diagram (each symbol represents the color of electro-generated species;⃞: [CoIIPc�2],⃝: [CoIPc�2]�1 D: [CoIPc�3]�2.

The isosbestic points at around 390, 550 and 690 nm in the spectraisolate during the reduction which indicates presence of more thanone reduced species. These species may be aggregated CoPc spe-cies. It is documented well in the literature that MPc complexes canaggregate especially in the non-coordinating solvent media, e.g.DCM. While mono anionic CoPc species generally give blue color[26e29], color of the CoPc studies here form green (point ⃝:x ¼ 0.3227 and y ¼ 0.3829) monoanionic form after the firstreduction process (Fig. 9c). Spectral changes during the secondreduction of CoPc studied here are very different than the CoPccomplexes in the literature. In the literature it is documented thatthe Q band of the CoPc decreased in intensity while a broad bandwas recorded at around 550 nm. However here, while the Q bandat 708 nm stays stable, the band at 675 nm increases in intensity.

A. Aktas et al. / Dyes and Pigments 99 (2013) 613e619 619

The band that is characterizing the CoI center at 475 nm stays asunchanged (Fig. 9b). The band at 475 nm indicates that after thesecond reduction process, the oxidation state of the cobalt center isone, thus the second reduction process should be a ring-basedreduction process. All band decreases are in intensity under theapplied potential at 1.00 V. Because under 1.00 V CoPc electro-polymerized on the working electrode, which caused to decrease ofthe CoPc concentration. Decreasing the concentration of CoPccauses to decreasing of the absorption bands. Color changes duringthe redox processes are represented in Fig. 9c.

4. Conclusion

In this study, the synthesis of new soluble metal-free 4 andmetallophthalocyanine (Zn, Ni, Co and Cu) 5e8 complexeswere described and these new complexes were characterized by IR,1H NMR, 13C NMR (just for phthalonitrile derivative), UVeVis(for phthalocyanine complexes) and MALDI-MS spectra. Electro-chemical and spectroelectrochemical measurement revealed thatincorporation redox active metal centers, CoII into the phthalocy-anine core extend the redox richness of the Pc ring with thereversible metal-based reduction and oxidation couples in additionto the common Pc ring-based electron transfer processes. Thisexpanded redox behavior of the complexes are the desired prop-erties of the electrochemical applications, especially, electro-catalytic, electrochromic and electrosensing applications. Allcomplexes 4e9 electro polymerized on the Pt working electrode.Type of the metal center of the complexes, potential window of thetechnique, and the cycle numbers of CV affect the character of thepolymerization processes. In-situ electrocolorimetric measure-ments of the new complexes allow quantification of color co-ordinates of the each electrogenerated anionic and cationic redoxspecies. Different color of the electrogenerated species indicatestheir possible application in the display technologies, e.g. electro-chromic and data storage application.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.dyepig.2013.06.033.

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