New electropolymerizable metal-free and metallophthalocyanines bearing {2-[3-(diethylamino)phenoxy]ethoxy } substituents

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Synthetic Metals 196 (2014) 166–172

Contents lists available at ScienceDirect

Synthetic Metals

jo ur nal homep age: www.elsev ier .com/ locate /synmet

ew electropolymerizable metal-free and metallophthalocyaninesearing {2-[3-(diethylamino)phenoxy]ethoxy} substituents

ekeriya Bıyıklıoglua,∗, Volkan C akıra, Faruk Demirb, Atıf Kocab

Department of Chemistry, Faculty of Science, Karadeniz Technical University, 61080 Trabzon, TurkeyDepartment of Chemical Engineering, Engineering Faculty, Marmara University, Göztepe, 34722 Istanbul, Turkey

r t i c l e i n f o

rticle history:eceived 20 March 2014eceived in revised form 21 July 2014ccepted 29 July 2014

eywords:

a b s t r a c t

In this work, metal-free and metallophthalocyanines (Ni, Co, Cu) bearing peripherally tetra substituted4-{2-[3-(diethylamino)phenoxy]ethoxy}groups were synthesized by cyclotetramerization of the corre-sponding phthalonitrile derivative and their electrochemical, spectroelectrochemical properties wereinvestigated. Phthalocyanines were characterized by a combination of IR, 1H-NMR, UV–vis and MS spec-tral data. Diethylamino groups on the substituents of the complexes cause electropolymerization of the

hthalocyanineynthesisiethylaminolectropolymerizationlectrochemistrypectroelectrochemistry

complexes on the working electrode during the oxidation reactions. Changing the potential windowof the voltammetric cycles alters the electropolymerization mechanisms. Types of the metal center ofthe complexes also affect the electropolymerization mechanism. Spectroelectrochemical measurementswere performed to assign the redox processes and spectroscopic responses of the electropolymerizationprocesses.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Metal-free and metallophthalocyanines are one of the mostseful heterocyclic materials. They show a wide range of techno-

ogical applications in different scientific areas for example solarells [1], electronic devices [2], liquid crystals [3], gas and chemi-al sensors [4], photo dynamic therapy (PDT) [5–9], electrochromicnd electroluminescent displays [10], non-linear optics [11], semi-onductors [12], photovoltaics [13] and their electrochemicalroperties [14,15] are utilized for electrochemical applicationsuch as electrocatalytic [16,17], electrosensing [18], electrochromicelds [19]. Electrochromism is an electrochemically producedtable and reversible color changes due to changing the opti-al responses of the electro-chromophores in the visible regionf the light spectrum. Electrochromic materials which includelectropolymerizable phthalocyanines [20] are used in differentpplications, such as various display technologies, energy-savingmart windows, sensors and data storage [21,22]. However, thepplications of metal-free and metallophthalocyanines is limited

y their low solubility in common organic solvents and water.ecause of this, one of the goals of research on the phthalocya-ines is to increase their solubility in common organic solvents

∗ Corresponding author. Tel.: +90 462 377 36 64; fax: +90 462 325 31 96.E-mail address: zekeriya [email protected] (Z. Bıyıklıoglu).

ttp://dx.doi.org/10.1016/j.synthmet.2014.07.023379-6779/© 2014 Elsevier B.V. All rights reserved.

and water. The solubility of metal-free and metallophthalocyaninescan be enhanced by introducing different kinds of substituentssuch as alkyl, alkoxy, phenoxy, macrocyclic groups [23–26] in com-mon organic solvents and amino, sulfo or carboxyl groups leads tophthalocyanine derivatives soluble in water [27–30].

Metallophthalocyanines (MPcs) are intensely studied as elec-trochemically functional materials due to the excellent redoxproperties [31–33]. Their electrochemical properties are easilyarranged by changing the metal center and types, number andposition of substituents. It is well documented that functionalmaterials should be coated on a substrate for their practical appli-cations [34–38]. Although many film coating techniques werestudies for the preparation of composite electrodes, prepara-tion of modified electrodes with electropolymerization is oneof the most preferred techniques [39–43]. Since it is easy tocontrol many of the film characters, such as morphology, thick-ness, conductivity, and polymer structure of the films [44,45].Although numerous different conjugated polymers, such as poly-thiophene [46–49], polyaniline [50–52], polypyrrole [50–52], werestudied for different applications, nowadays metal-containingconjugated polymers, especially polymerized MPcs have takencondensed attentions [53–59] Some examples of porphyrin and

phthalocyanine-containing conjugated polymers have been alsoreported [60–67]. Applications of modified electrodes based onelectropolymerization of functional materials canalized our stud-ies to synthesis of MPcs bearing electropolymerizable substituents.

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or this purpose we reported different MPcs bearing thiophene68,69], amino [70], and quinolin [71] moieties. Now in this paper,e have synthesized new MPcs bearing electropolymerizable 4-

2-[3-(diethylamino)phenoxy]ethoxy}groups and then we havenvestigated electrochemical and spectroelectrochemical proper-ies of these novel complexes. Finally we aimed to prepare modifiedlectrodes with electropolymerization of the MPcs for the possiblepplications of the complexes in different electrochemical tech-ologies.

. Experimental

.1. Synthesis

.1.1. Synthesis of metal-free phthalocyanine (4)4-{2-[3-(Diethylamino)phenoxy]ethoxy}phthalonitrile 3 (0.4 g,

.19 × 10−3 mol) and five drops of 1.8-diazabicyclo[5.4.0]undec--ene (DBU) in 0.004 L of dry n-pentanol was heated and stirredt 160 ◦C for 12 h under N2. After cooling to room temperature

he product was precipitated with ethanol and then dried inacuo. Lastly, pure metal-free phthalocyanine was obtained byolumn chromatography which is placed aluminum oxide usingHCl3:CH3OH (100:1) as solvent system. Yield: 0.175 g (44%). IR

N

OOH

CN

CN

O2N

1

2

i

N

N

O

O

N

O

O

Fig. 1. The synthetic route of the metal-free phthalocyanine. Reagents and co

etals 196 (2014) 166–172 167

(KBr tablet) �max/cm−1: 3292 (N H), 3073 (Ar H), 2965 − 2868(Aliph. C H), 1610, 1571, 1499, 1481, 1450, 1356, 1276, 1213, 1142,1096, 1071, 1014, 951, 823, 748, 686. 1H-NMR. (CDCl3), (ı: ppm):7.28 − 7.14 (m, 12H, Ar H), 6.50 − 6.23 (m, 16H, Ar H), 4.38 (m,16H, CH2 O), 3.43 (m, 16H, CH2 N), 1.27 (m, 24H, CH3) −5,38(bs, 2H, N H). UV–vis (chloroform): �max, nm (log ε): 338 (4.85),608 (4.43), 643 (4.61), 667 (4.90), 704 (4.95). MALDI-TOF-MS (2,5-dihydroxy benzoic acid as the matrix) m/z: 1344 [M + H]+.

2.1.2. General procedures for metallophthalocyanine derivatives(5–7)

A mixture of 4-{2-[3-(diethylamino)phenoxy]ethoxy}phthalo-nitrile 3 (0.3 g, 0.89 × 10−3 mol), four drops of 1.8-diazabicyclo-[5.4.0]undec-7-ene (DBU) in 0.003 L of n-pentanol and anhydrousmetal salts [NiCl2 (0.057 g), CoCl2 (0.058 g), CuCl2 (0.060 g)] wereheated and stirred at 160 ◦C for 12 h under N2. After cooling to roomtemperature, the reaction mixture was precipitated by adding itdrop-wise into ethanol. The precipitated green solid product was

filtered off, and then dried in vacuo over P2O5. Finally, pure metallo-phthalocyanines were obtained by column chromatography whichis placed aluminum oxide using CHCl3:CH3OH (100:2) as solventsystem.

N

OO

CN

CN

3

ii

N

HN

N

NNH

N

N

N

O

O

N

O

O

4

nditions: (i) dry DMF, K2CO3, 50 ◦C, 96 h; (ii) n-pentanol, DBU, 160 ◦C.

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68 Z. Bıyıklıoglu et al. / Synth

.1.3. Nickel(II) phthalocyanine (5)Yield: 0.175 g (56%). IR (KBr tablet) �max/cm−1: 3076 (Ar H),

965 − 2867 (Aliph. C H), 1610, 1571, 1499, 1351, 1274, 1214,127, 1094, 1070, 1022, 977, 821, 750, 686. 1H-NMR. (CDCl3), (ı:pm): 7.33-7.15 (m, 12H, Ar H), 6.58 − 6.30 (m, 16H, Ar H), 4.19m, 16H, CH2 O), 3.26 (m, 16H, CH2 N), 1.11 (m, 24H, CH3).V–vis (chloroform): �max, nm (log ε): 329 (4.78), 622 (4.67), 672

4.96). MALDI-TOF-MS (2,5-dihydroxy benzoic acid as the matrix)/z: 1400 [M]+.

.1.4. Copper(II) phthalocyanine (7)Yield: 0.163 g (52%). IR (KBr tablet) �max/cm−1: 3071 (Ar H),

963 − 2867 (Aliph. C H), 1609, 1570, 1500, 1449, 1400, 1343,274, 1214, 1124, 1094, 1068, 974, 823, 746, 685. UV–vis (chlo-oform): �max, nm (log ε): 337 (4.89), 621 (4.69), 681 (4.97).ALDI-TOF-MS (2,5-dihydroxy benzoic acid as the matrix) m/z:

405 [M]+.

. Results and discussion

.1. Synthesis and characterization

The synthesis route of 2-[3-(diethylamino)phenoxy]ethoxyubstituted phthalonitrile 3, its target metal-free 4 and metal-ophthalocyanines 5–7 is shown in Figs. 1 and 2. The noveleripherally tetra-substituted metal-free, nickel(II), cobalt(II) andopper(II) phthalocyanines were obtained by cyclotetramerizationf 4-{2-[3-(diethylamino)phenoxy]ethoxy}phthalonitrile [72] 3 in-pentanol in the presence of DBU and metal salts (NiCl2, CoCl2,uCl2) under reflux for 12 h. The structures of the new compoundsere confirmed using UV–vis, IR, 1H-NMR, 13C-NMR, MS spec-

roscopic data. The analysis results are in accordance with theredicted structures as shown in the experimental section.

The IR spectrum of the metal-free phthalocyanine 4 showed

sual inner core-NH peak at 3292 cm−1, this is characteristic foretal-free phthalocyanines. The 1H NMR spectrum of metal-free

hthalocyanine 4 indicates the typical shielding of inner corerotons as a broad signal at around ı = −5.38 ppm which could

N

OO

CN

CN

3

iii

N

O

N

O

Fig. 2. The synthetic route of the nickel, cobalt and copper phthalocyanines. Re

etals 196 (2014) 166–172

be attributed to the N H resonances [73]. The disappearance ofthe C≡N vibration of compound 3 at 2229 cm−1 in the IR spec-trum of the nickel(II), cobalt(II) and copper(II) phthalocyanines 5–7demonstrates the formation of these phthalocyanines. The 1H-NMRspectrum of nickel(II) phthalocyanine 5 was almost similar to themetal-free phthalocyanine 4. The 1H NMR spectrum of cobalt andcopper phthalocyanines 6, 7 could not be determined due to theparamagnetic cobalt(II) and copper(II) centers [74]. In the massspectrum of peripherally tetra-substituted metal-free and metal-lophthalocyanines 4, 5, 6 and 7, the molecular ion peaks wereobserved at m/z = 1344 [M + H]+, 1400 [M]+, 1401 [M + H]+, 1405[M]+, respectively confirmed the targeted structures.

UV–vis spectroscopy is one of the best evidence for the char-acterization of metal-free and metallophthalocyanines. Generally,metal-free and metallophthalocyanines have two strong absorp-tion regions, one of them in the UV region at about 300–350 nm(B band) and the other one in the visible region at 600–700 nm (Qband). The electronic absorption spectrum of the metal-free andmetallophthalocyanines 4, 5, 6 and 7, in chloroform at room tem-perature is shown in Fig. 3. In the UV–vis spectra of metal-free andmetallophthalocyanines 4–7 (in CHCl3) Q bands were observed at(704, 667), 672, 674, 681 nm, respectively as singlet with shoul-ders at (643, 608), 622, 622, 621 nm, respectively. UV–vis spectraof metal-free and metallophthalocyanines 4–7 (in CHCl3) exhibitedB bands between 338 and 329 nm.

3.2. Voltammetric measurements

To perform an electrochemical characterization for the pro-posed structure of the complexes, redox behaviors of the complexeswere performed in DCM/TBAP electrolyte system on a Pt workingelectrode. Voltammetric analyses were tabulated in Table 1 withthe similar complexes in the literature for comparison. As shown inTable 1 fundamental voltammetric parameters, especially E1/2 and

�E1/2 values of the complexes are in agreements with the similarcomplexes in the literature [75–77], which support the proposedstructures of the complexes. It is well documented in the litera-ture that, phthalocyanines bearing 2H+, Ni2+, and Cu2+ ions in the

Compound

M Co

5

N

N

N

NN

N

M

N

N

O

O

N

O

O

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O

O

CuNi

6 7

agents and conditions: (iii) n-pentanol, DBU, 160 ◦C, NiCl2, CoCl2, CuCl2.

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anodic potentials are scanned after the cathodic potentials con-tinuously, CuPc is electropolymerized on the working electrode(Fig. 6a). Electropolymerized waves increase up to 11. CV cycleswith a potential shift. During electropolymerization reaction, redox

Fig. 3. UV–vis spectrum

ore and redox inactive substituents give only ring-based reduc-ion and oxidation processes which have �E1/2 values at around.50 V. H2Pc, CuPc and NiPc complexes studied here obey thisehavior. General similarities of the complexes are the aggrega-ion of the complexes. Especially the first reduction couples of theomplexes deviates from reversibility due to the aggregation. Allomplexes are oxidative electropolymerized on the working elec-rode. Applied potential ranges and metal center of the complexesffect the polymerization mechanism.

Fig. 4 illustrates CV responses of H2Pc. It displays two quasi-eversible couples (R1 at −0.76 V and R2 at −1.08 V) during theathodic potential scans. During the first anodic scans, it givesn anodic wave at 0.74 V and its reverse cathodic wave at 0.65 V.uring the repetitive potential scans, a new huge anodic wave is

ecorded at 0.63 V, which increases with positive potential shift upo 5. CV cycles and collapsed the wave at 0.74 V (Fig. 4). At theame time new wave is observed at −1.12 V with increasing in cur-ent intensity. After the 5. CV cycles, these waves starts to decreaseith potential shifts. These voltammetric data indicate electropoly-erization of the complex on the working electrode. While H2Pc

issolves in DCM very well, electropolymerized H2Pc is insoluble

n the same solvent.

CuPc and NiPc also give two reduction reactions and elec-ropolymerized during the oxidation reactions. Main differencesf the voltammetric responses are the aggregation of CuPc and

able 1oltammetric data of the complexes. All voltammetric data were given versus SCE.

Complex Polymerization waves Ring reductions

H2Pc aE1/2 – 0.76d (0.65)e −0.76 −1.08b�Ep (mV) – – 75 84cIp,a/Ip,c – – 0.96 0.92

NiPc aE1/2 – 0.86d (0.62)e −0.97 −1.26b�Ep (mV) – – 110 96cIp,a/Ip,c – – 0.92 0.97

CuPc aE1/2 – 0.85d (0.61)e −0.96 −1.22b�Ep (mV) – – 100 110cIp,a/Ip,c – – 0.96 0.91

a E1/2 values ((Epa + Epc)/2) were given versus SCE and Fc/Fc+ (in parenthesis) at.100 V s−1 scan rate.b �Ep = Epa − Epc.c Ip,a/Ip,c for reduction, Ip,c/Ip,a for oxidation processes.d Epa of first CV cycle.e Epc of first CV cycle.

, 6 and 7 in chloroform.

NiPc. Due to the aggregation, the first reduction reactions ofthese complexes have irreversible characters. Electropolymeriza-tion behaviors of the complexes also differ due to the differentmetal center of the complexes. As shown in Fig. 5, CuPc gives anirreversible reduction (R1 at −0.96 V) followed with a reversibleone (R2 at −1.22 V) during the cathodic scans. However when

Fig. 4. (a) Repetitive CVs of H2Pc recorded with in the whole potential windows ofDCM/TBAP electrolyte system at 0.100 V s−1 scan rate on a Pt working electrode.(b) Repetitive CVs of H2Pc recorded at anodic potential windows of DCM/TBAPelectrolyte system at 0.100 V s−1 scan rate on a Pt working electrode.

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Fig. 5. (a) CVs of CuPc recorded at cathodic potentials at various scan rates on a Ptworking electrode in DCM/TBAP and (b) SWV of CuPc recorded with SWV parame-ters: step size = 5 mV; pulse size = 100 mV; frequency = 25 Hz.

Fig. 6. (a) Repetitive CVs of CuPc recorded with in the whole potential windows ofDCM/TBAP electrolyte system at 0.100 V s−1 scan rate on a Pt working electrode.(b) Repetitive CVs of CuPc recorded at anodic potential windows of DCM/TBAPelectrolyte system at 0.100 V s−1 scan rate on a Pt working electrode.

Fig. 7. (a) Repetitive CVs of NiPc recorded with in the whole potential windows of

DCM/TBAP electrolyte system at 0.100 V s−1 scan rate on a Pt working electrode.(b) Repetitive CVs of NiPc recorded at anodic potential windows of DCM/TBAPelectrolyte system at 0.100 V s−1 scan rate on a Pt working electrode.

wave of CuPc disappears completely and new waves attributed tothe electropolymerized film are recorded. Electropolymerized filmof CuPc is insoluble in DCM like H2Pc. When the positive potentialsare scanned instead of the whole potential window of the elec-trolyte system, polymerization mechanism changes as shown inFig. 6b. Shifting of the redox wave of CuPc is smaller and the redoxprocess of the polymerization reaction is more reversible when onlyanodic potentials are scanned.

Fig. 7 shows the voltammetric responses of NiPc. Reduction pro-cesses of NiPc are more reversible than CuPc, but less reversiblethan those of H2Pc. It gives the first reduction reaction (R1) at−0.97 V with �Ep of 110 mV and the second reduction reaction (R2)at −1.26 V with �Ep of 90 mV. Easy of reduction order of these com-plex is H2Pc > CuPc > NiPc. During the anodic potential scans, NiPcgives a huge oxidation wave, which increases in current intensitywith repetitive CV cycles (Fig. 7b). Changing the potential windowof the potential scan changes the polymerization mechanism ofNiPc, like those of H2Pc and CuPc. Although monomeric NiPc is sol-uble in DCM, polymerized film on the working electrode is insolublein the same solvent.

3.3. Spectroelectrochemistry

In situ spectroelectrochemical studies were employed to per-form assignments of the electron transfer reactions recorded with

CV and SWV measurements. It is well documented that H2Pc,CuPc and NiPc complexes. Fig. 8 represents in situ UV–vis spectralchanges and in situ recorded chromaticity diagram of H2Pc. With-out any potential application, H2Pc shows a split Q band at 670

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F Eapp = = −1.50 V. (b) Eapp= = 1.50 V. (d) Chromaticity diagram (each symbol represents thec H2Pc−1]+1.

ardaf−bisiat

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ig. 8. In-situ UV–vis spectral changes of H2Pc in DCM/TBAP. (a) Eapp = −1.10 V. (b)olor of electro-generated species; �: [H2Pc−2], ©: [H2Pc−2]−1; �: [H2Pc−3]−2; �: [

nd 70 nm with a shoulder at 637 nm. During the first reductioneaction at −1.00 V, Q band the split Q band turn to a single bandue to increasing a sharp band at 677 nm. These spectral changesre characteristic changes for the first reduction reaction of metalree phthalocyanines (Fig. 8a) [78–80]. Upon applied potential of1.40 V, while the Q band at 677 nm decreases in intensity, newands are recorded at 675, 800, and 880 nm. Spectral changes given

n Fig. 8b are easily assigned to the reduction of dianionic H2Pcpecies. All bands decreases in intensity due to the electropolymer-zation of the H2Pc during the oxidation reaction at 1.10 V potentialpplication (Fig. 8c). Color changes due to the electron transfer reac-ions of H2Pc are illustrated in the chromaticity diagram (Fig. 8d).

CuPc and NiPc complexes gave very similar spectral changesuring in-situ spectroelectrochemical measurements. Both com-lexes electropolymerized during the oxidation processes and allands in the spectra of these complexes decrease in intensity dueo the polymerization. During the reduction reactions both com-lexes gave spectral changes assigned to the Pc ring reductioneactions. In-situ spectroelectrochemical results of CuPc are givens a representative of these complexes in Fig. 9. Before any poten-ial application, CuPc gives the Q band at 678 nm and a shoulder at21 nm. Due to the aggregation of the complex intensity of the bandt 621 nm is higher than the Q band of the monomeric species. Thispectral behavior supports aggregation effects to the CV responsesf the complex. During the first reduction reaction, while the Qand at 678 nm and the band at 621 nm decrease in intensity a newand is recorded at 582 nm. Moreover, two new bands are observed

t 887 and 951 nm. These spectral changes indicated reduction ofoth aggregated and monomeric CuIIPc−2 species to the monomericuIIPc−3 (Fig. 9a) [81–84]. During the second reduction reaction,hile the Q band and its shoulder decrease, two new bands increase

Fig. 9. In-situ UV–vis spectral changes of CuPc in DCM/TBAP. (a) Eapp = –1.00 V. (b)Eapp = –1.50 V.

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t 800 and 890 nm. At the same time the bands at 582 and 951 nmecreases in intensity (Fig. 9b). These are the characteristic changesor the reduction of monoanionic CuIIPc−3 to dianionic CuIIPc−4

pecies.

. Conclusion

In this study, we have reported the synthesis, electrochemicalnd spectroelectrochemical properties of metal-free, nickel, cobaltnd copper phthalocyanines. Phthalocyanines were characterizedy a combination of IR, 1H-NMR, UV–vis and MS spectral data. Elec-rochemical and spectroelectrochemical measurement indicateshat substitution of the complexes with dimethylamine groupsupply electropolymerization of the complexes on the workinglectrode. By means of electropolymerization complexes can beandidate for the usage in different electrochemical technologiesuch as, electrocatalytic, electrochromic and electrosensing appli-ations.

cknowledgments

We thank to TUBITAK and TUBA for their financial supportProject nos: 111T963 and 2010-01-02-GEP03).

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