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Electrochemistry, electropolymerization and electrochromism of novel phthalocyanines bearing morpholine groups
Journal of Molecular Structure 1206 (2020) 127674
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Electrochemistry, electropolymerization and electrochromism of novel phthalocyanines bearing morpholine groups Duygu Akyüz a, b, Ümit Demirbas¸ c, *, Atıf Koca a, Fatih Çelik c, Halit Kantekin c _ Department of Chemical Engineering, Engineering Faculty, Marmara University, Istanbul, Turkey Department of Chemistry, Faculty of Science, Gebze Technical University, Kocaeli, Turkey c Department of Chemistry, Faculty of Science, Karadeniz Technical University, Trabzon, Turkey a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 October 2019 Received in revised form 28 December 2019 Accepted 30 December 2019 Available online 3 January 2020
In this work, 4-(4-((4-morpholinophenylimino)methyl)phenoxy)phthalonitrile (3) and it’s peripherally tetra substituted metal-free (4), zinc(II) (5), copper(II) (6) and nickel(II) (7) phthalocyanines were synthesized for the first time. The structural characterization of these novel compounds were performed with FT-IR, 1H NMR, 13C NMR, UVeVis and mass spectroscopy. Electrochemical and spectroelectrochemical characterizations of phthalocyanines (4e7) showed that while all phthalocyanines went to characteristics phthalocyanine ring and/or metal based reduction processes during the negative potential scans, all complexes were coated on the working electrode during the oxidation processes due to the cationic electropolymerizations of the 4-(4-((4-morpholinophenylimino)methyl)phenoxy) substituents. Changing the metal centers of phthalocyanine ring influenced the redox processes due to the different redox activities and effective nuclear charges of the metal centers. In addition to the electropolymerization ability of 4-(4-((4-morpholinophenylimino)methyl)phenoxy) substituent slightly affected the reversibility and peak positions of the redox processes. Indium tin oxide coated glass electrode (ITO) was coated with electropolymerized films of phthalocyanines to construct ITO/PolyPhthalocyanine and these electrodes were tested as a potential electrochromic material. ITO/PolyPhthalocyanine provided color change between green and blue with 1.2 s switching time, 18% optical contrast and 100% optical stability with 50 cronoamperometric (CA) cycles. These studies indicated possible usage of the electropolymerized films of phthalocyanines as possible building blocks for advanced electrochromic devices needing green-blue color change. © 2020 Elsevier B.V. All rights reserved.
Keywords: Morpholine Metallo-phthalocyanines Electrochemistry Spectroelectrochemistry (Oxidative) electropolymerization
1. Introduction Since their discovery, phthalocyanines (Pcs) have been important compounds for scientists. Phthalocyanines are aromatic heterocyclic compounds consisting of isoiminoindole moieties [1]. Phthalocyanine ring has a strong electron delocalization. This 18 p electronic conjugation imparts significant thermal, photo and electrochemical properties to Pcs [2]. Thanks to these features phthalocyanines can be used in many different applications such as solar cells [3], chemical sensors [4e6], liquid crystals [7], non-linear optics [8], laser dyes [9], catalyst [10], photo-voltaic optics [11], optical storage devices [12] and semiconductors [13]. Morpholines are six-membered ring compounds containing
* Corresponding author. E-mail address: [email protected] (Ü. Demirbas¸). https://doi.org/10.1016/j.molstruc.2019.127674 0022-2860/© 2020 Elsevier B.V. All rights reserved.
nitrogen and oxygen atoms. Thanks to their biological and pharmacological features morpholines can be used in many applications such as tyrosinase inhibitory [14], antioxidant [15], antiinflammatory [16]. In addition, electrochemical features of morpholines are significant. There are many studies in the literature that containing morpholine substituted compounds are used in electrochemical applications [17e19]. In this study, we have intended to synthesize 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituted phthalocyanines and investigate their electrochemical and spectroelectrochemical properties for the first time. Their electrochemical responses were determined in order to enhance the redox worth and to facilitate the medications of electrodes with electropolymerization of the phthalocyanines.
2
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
2. Experimental The used equipments, materials and synthesis were given as supplementary materials in detail. 2.1. Electrochemical, in-situ spectroelectrochemical and electrocolorimetric measurements Cyclic voltammetric (CV), square wave voltammetric (SWV) and in-situ spectroelectrochemical (SEC) measurements were carried out according to following procedure [20]. Glassy carbon electrode
(GCE) used as working electrode with electrode surface area of 0.071 cm2 for all voltammetric measurements. The platinum wire and silver-silver chloride (Ag׀AgCl) electrode were employed as counter, and reference electrode, respectively in voltammetric measurements. Measurements were carried out in dichloro methane (DCM) containing tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte at a concentration of 0.10 mol/ dm3 under pure nitrogen atmosphere. In situ SEC and electrocolorimetric (EC) measurements were carried out in homemade quartz cell by using a Reference 600 Gamry potentiostat and QE65000 OceanOptics diode array spectrophotometer. Indium tin
Scheme 1. Synthetic route for novel compounds (3e7).
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
3
oxide (ITO) glass electrode (surface area of 0.80 cm2), a platinum wire counter and a silver-silver chloride (Ag׀AgCl) reference electrode were used for the SEC measurements. SEC and EC measurements were carried out in ultra pure water (18 mU, milipore) solution including LiClO4 at concentration 0.10 mol/dm3. 2.2. Electrode modification with electropolymerization Electropolymerization technique was employed for the electrode modification by following paper [21]. For the formation of ITO/Poly-Pcs, Pc solution was electropolymerized on the ITO surface with repetitive 10 CVs in the electrochemical cell containing 5.0 104 mol dm3 Pc in DCM solution. CV scans were performed between 1.50 and 0.50 V at 100 mV s1 scan rate on ITO electrode. The non-electropolymerized Pc species were removed from the ITO/Poly-Pc electrode by washing with DCM and water respectively and finally it was dried in an oven under atmospheric conditions at 25 C. 3. Results and discussion 3.1. Synthesis and characterization The synthesis of novel compounds (3e7) was displayed in Scheme 1. The compound (3) was prepared with the reaction between 4-((4-morpholinophenylimino)methyl)phenol (1) and 4nitrophthalonitrile (2). In the IR spectrum, the new vibrations were observed at 2232 cm1 and the 13C NMR signals appeared at 115.891 and 112.456 ppm showed that compound (3) has nitrile (-C^N) groups. In the 1H NMR spectrum the new aromatic protons demonstrated that phthalonitrile (3) was successfully prepared. In NMR spectra aromatic and aliphatic protons and carbon signals showed expected values. The [MþH]þ mass peak confirmed the structure of compound (3). All characterization data are in accordance with the literature about the substituted phthalonitriles [22,23]. The novel phthalocyanines (4e7) were prepared with a cyclotetramerization reaction of phthalonitrile compound (3) in npentanol. They were characterizated by a combination of FT-IR, 1H NMR, UveVis and mass spectral data. The completion of cyclotetramerization reaction was confirmed by the disappearance of eC^N vibrations in the IR spectra of phthalocyanines (4e7). In addition, the vibrations were shown at 3290 cm1 in the IR spectrum of metal-free phthalocyanine (4) was confirmed the proposed structure of compound. Aromatic and aliphatic protons demonstrated expected signals in the 1H NMR spectra of compound (4, 5 and 7). In addition, because of the presence of paramagnetic copper(II) ions the 1H NMR measurements of compounds (6) could not be performed [24]. On the other hand the inner core protons of compound (4) could not be observed in the 1H NMR spectrum due to the strong aggregation between phthalocyanine molecules [25]. The observed [M]þ and [MþH]þ peaks in the mass spectra
Table 1 Voltammetric data of the complexes in DCM solutions. All data were given versus AgǀAgCl. Complexes
a
E1/2 of Redox couples
Oxd. of substituents H2Pc (4) ZnPc (5) CuPc (6) NiPc (7) a
1.15 e 1.12 1.13
Oxd1
Red1
Red2
0.60 0.57 0.57 0.56
0.55 0.83 0.71 0.75
0.84 1.21 0.98 1.05
Fig. 1. a) CVs and b) SWVs of H2Pc (5.0 104 mol dm3) recorded at various scan rates and on a GCE electrode in DCM/TBAP.
Fig. 2. Repetitive CV of H2Pc (5.0 104 mol dm3) recorded at 100 mVs1 scan rate on a GCE in DCM/TBAP.
confirmed the structures of compounds (4e7). The UVeVis spectra of compounds (4e7) were as expected. All characterization data are in accordance with the literature about the phthalocyanines [26,27]. 3.2. Voltammetric measurements
0.94 0.98 0.94 0.96
E1/2 values (Epa þ Epc)/2) were recorded at 100 mV s1 scan rate.
Voltammetric analyses of Pcs (4e7) bearing tetra 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent were carried out with CV and SWV in DCM/TBAP electrolyte on GCE working electrode. The basic electrochemical parameters were derived from
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D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
the voltammograms and they were tabulated in Table 1. As shown in Table 1, while all complexes show clear Pc based reduction peaks during the cathodic potential scans, they were electropolymerized during the anodic potential scans. Fig. 1 represents CVs and SWVs of H2Pc (4). H2Pc (4) illustrates two reversible reduction processes at negative potentials at 0.55 V and 0.84 V, which are assigned to [H2Pc2]/[H2Pc3]1and [H2Pc3]1-/[H2Pc4]2- couples. During the positive potential scans, the Pc oxidation process of [H2Pc2]/[H2Pc1]1þ at 0.60 V is followed with a huge substituent oxidation wave at 1.08 V. 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent have polymerization ability, thus their possible electropolymerization process is carried out with repetitive CV measurements, which is represented in Fig. 2. As shown in this figure, during the first CV cycle, the oxidation waves of the 4-(4-((4-morpholinophenylimino) methyl)phenoxy) substituent are observed at 0.94 and 1.15 V. Due to the polymerization of the cationic species created during the oxidation process, the oxidation waves of the polymer are observed at 0.90 and 1.12 V during the second CV cycle. These new waves and their corresponding reduction couple increase in current intensity with small potential shifts with respect to increasing CV cycle numbers. Until 40 CV cycles, two quasi-reversible couple is observed for the electropolymerized film on the electrode surface. These voltammetric responses illustrate formation of a redox active and conductive poly-[H2Pc2] film on GCE surface with cationic electropolymerization of 4-(4-((4-morpholinophenylimino) methyl)phenoxy) substituent of [H2Pc2]. Electrochemical behaviour of H2Pc is consistent with literature. It is reported that H2Pc gives two reduction reaction and one oxidation reaction in the result of the electrochemical characterization [28,29]. The ligands
including morpholine groups generally polymerize during the oxidation reaction. For example, metallo-phthalocyanine complex including 5-{[(1E)-(4-morpholin-4-ylphenyl)methylene]amino}-1naphthoxy substituent was electropolymerized on GCE [30]. Z. Biyiklioglu and et al. synthesized BODIPY dyes containing 4morpholin-4-yl-benzyl and 4-(dimethylamino)-1-naphthyl and they electropolymerized on working electrode [31]. Changing the Hþ center of Pc ring with Zn2þ, Cu2þ and Ni2þ cations slightly decrease the reversibility of the reduction processes with negative potential shifting due to the changing of the effective nuclear charge of the cations in the core of Pc ring. All of these complexes give two Pc based reductions and one Pc based oxidation processes in addition to the oxidation waves of 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent. Fig. 3 shows CVs and SWVs of NiPc (7) as an example. Reduction peaks of NiPc (7) are observed at 0.75 V for [NiPc2]/[NiPc3]1and 1.06 V for [NiPc3]1-/[NiPc4]2- couples. [NiPc2]/[NiPc3]1-
Fig. 3. a) CVs and b) SWVs of NiPc(5.0 104 mol dm3) recorded at various scan rates on a GCE in DCM/TBAP.
Fig. 4. Repetitive CV of a) CuPc, b) ZnPc, and c) NiPc(5.0 104 mol dm3) recorded at 100 mVs1 scan rate on a GCE in DCM/TBAP.
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
couple at is followed with the oxidation waves of substituents at 0.96 and 1.20 V. As shown in Fig. 4c, NiPc (7) is also electropolymerized due to the cationic polymerization of the cations of 4(4-((4-morpholinophenylimino)methyl)phenoxy) substituents. CuPc (6), ZnPc (5) and NiPc (7) illustrates similar electropolymerization features with small changes, which is stem from effect of metal center, as shown in Fig. 4. Generally, two oxidation waves are observed for the electropolymerized films of all complexes, but due to the siftings of the first oxidation wave, these oxidation peaks are overlapped and form a broad wave with increasing CV cycles. As shown in Table 1, CuPc (6) and ZnPc (5) complexes give similar voltammetric responses with slight changes on the redox potentials. Electrochemical responses of CuPc (6) and ZnPc (7) are given in Fig. S1 and Fig. S2. 3.3. Spectroelectrochemical and electrocolorimetric measurements To illustrate electrochromic responses of Pcs (4e7) spectroelectrochemical and electrochemical measurements were performed in LiClO4/H2O electrolyte. Electrochromic electrodes were prepared by electropolymerizations of Pcs (4e7) on ITO electrodes and then ITO/Poly-Pcs were tested as possible electrochromic materials. All complexes (4e7) illustrated similar responses thus
5
electrochromic measurements results of ITO/Poly-NiPc are shown in Fig. 5. Transmittance changes of ITO/Poly-NiPc electrode under applied potential is given in Fig. 5a. The neutral ITO/Poly-NiPc electrode gives three bands at 443, 638 and 685 nm which are the characteristic bands of NiPc (7). When 1.50 V was applied to the working electrode, while the existence bands increase in T% intensity, the region at around 550 nm decreases. These spectral changes cause to a color change from green to blue. In order to investigate electrochromic parameters, repetitive CA excitations were employed between 0.0 V and 1.50 V with 30 s intervals. During CA measurements, ‘T% versus time’ and ‘Current (I) versus time’ responses were measured. As shown in Fig. 5b, symmetric anodic and cathodic currents were observed for each CA cycle and coulombic stability decrease as 34% within 50 CA excitations. In order to determine optical stability, response time, and optical contrasts, T% -time changes were also measured at 680 nm during the CA excitations. As shown in Fig. 5c, difference between maximum and minimum T% values give the optical contrast as 18% and the optical contrast keeps its stability with in the 50 CA cycles. Response times are measured as 1.20 s and 4.20 s for anodic and cathodic color changes respectively at 680 nm. The color efficiency (h) that is one of important parameter in electrochromic materials, and is calculated according to the following equation [32]
Fig. 5. a) SEC (T% vs. wavelength changes) measurement, b) CA responses of ITO/Poly-NiPc electrode between Eapp ¼ 0.00 V (time ¼ 30 s) and Eapp ¼ 1.50 V (time ¼ 30 s) c) T% versus time responses of ITO/Poly-NiPcin LiClO4/H2O electrolyte system.
6
h¼
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
DOD Qd
(1)
where, DOD is the ratio of optical density contrast and Qd is to charge consumed per unit area (Qd) during an electrochromic transition by using CA measurement. It is calculated for ITO/PolyNiPc electrode and is estimated as 94.57 cm2C-1 for 680 nm. Electrochromic responses of CuPc (6) and ZnPc (7) are given in Fig. S3 and Fig. S4. 4. Conclusions In this study, 4-(4-((4-morpholinophenylimino)methyl)phenoxy)phthalonitrile (3) and it’s peripherally tetra substituted metal-free (4), zinc(II) (5), copper(II) (6) and nickel(II) (7) phthalocyanines were synthesized for the first time. The structural characterization of these novel compounds were performed with FT-IR, 1H NMR, 13C NMR, UVeVis and mass spectroscopy. Electrochemical measurements indicated that Pcs (4e7) illustrate very similar characteristic Pc ring based reduction and oxidation processes. All complexes illustrated two reduction reaction during the cathodic potential scans and they showed similar electropolymerization responses. Changing the metal centers only influenced reversibility and position of the redox couples. 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent triggered electropolymerization of the complexes during the oxidation reactions. Electropolymerized films illustrates electrochromic color changes between green and blue colors. Electrochromic efficiency of NiPc was observed considerably higher than those of ZnPc (5) and CuPc (6). CRediT authorship contribution statement Duygu Akyüz: Visualization, Writing - original draft, Writing review & editing, Investigation. Ümit Demirbas¸: Project administration, Visualization, Writing - original draft, Writing - review & editing, Resources, Investigation, Conceptualization. Atıf Koca: Visualization, Writing - original draft, Writing - review & editing, Resources, Investigation, Conceptualization. Fatih Çelik: Visualization, Writing - original draft, Writing - review & editing, Resources, Conceptualization. Halit Kantekin: Visualization, Writing - original draft, Writing - review & editing, Resources, Investigation, Conceptualization. Acknowledgements Atıf Koca thanks Turkish Academy of Sciences (TUBA) for support. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.127674. References [1] N.B. McKeown, Phthalocyanine Materials: Synthesis, Structure, and Function, Cambridge University Press, Cambridge, 1998. [2] A.L. Thomas, Phthalocyanine Research and Applications, CRC Press, Boca Raton, Florida, 1990. [3] F. Yang, S.R. Forrest, Photocurrent generation in nanostructured organic solar cells, ACS Nano 2 (2008) 1022e1032. [4] C.C. Leznoff, A.B.P. Lever, Phthalocyanines Properties and Applications, vol. 1, VCH Publisher, New York, 1989.
ndez, J.A. Saja, On the effect of [5] V. Parra, M. Bouvet, J. Brunet, M.L. Rodríguez-Me ammonia and wet atmospheres on the conducting properties of different lutetium bisphthalocyanine thin films, Thin Solid Films 516 (2008) 9012e9019. [6] M. Bouvet, Phthalocyanine-based field-effect transistors as gas sensor, Anal. Bioanal. Chem. 384 (2006) 366e373. [7] C.C. Leznoff, A.B.P. Lever, Phthalocyanines Properties and Applications, vol. 2, VCH Publisher, New York, 1993. [8] G. De La Torre, P. Vazquez, F. Agullo-Lopez, T. Torres, Phthalocyanines and related compounds:organic targets for nonlinear optical applications, J. Mater. Chem. 8 (1998) 1671e1683. [9] C.C. Leznoff, A.B.P. Lever, Phthalocyanines, Properties and Applications, vol. 4, VCH Publisher, New York, 1996. € € Bekarog _ Kani, O. lu, Catalytic activity of a thermo[10] F. Yılmaz, M. Ozer, I. regulated, phase-separable Pd(II)-perfluoroalkylphthalocyanine complex in an organic/fluorous biphasic system: hydrogenation of olefins, Catal. Lett. 130 (2009) 642e647. [11] S.R. Forrest, Ultrathin organic films grown by organic molecular beam deposition and related techniques, Chem. Rev. 97 (1997) 1793e1896. [12] M. Emmelius, G. Pawlowski, H.W. Vollmann, Materials for optical-data storage, Angew. Chem. Int. Ed. 28 (1989) 1445e1471. [13] S. Nagel, M. Lener, C. Keil, R. Gerdes, L. Lapok, S.M. Gorun, Electrochromic switching of evaporated thin films of bulky, electronic deficient metallophthalocyanines, J. Phys. Chem. C 115 (2011) 8759e8767. [14] H. Hamidian, S. Azizi, Synthesis of novel compounds containing morpholine and 5(4H)-oxazolone rings as potent tyrosinase inhibitors, Bioorg. Med. Chem. 23 (2015) 7089e7094. [15] E.M. Ladopoulou, A.N. Matralis, A. Nikitakis, A.P. Kourounakis, Antihyperlipidemic morpholine derivatives with antioxidant activity: an investigation of the aromatic substitution, Bioorg. Med. Chem. 23 (2015) 7015e7023. [16] K. Dhahagani, S.M. Kumar, G. Chakkaravarthi, K. Anitha, J. Rajesh, A. Ramu, G. Rajagapal, Synthesis and spectral characterization of Schiff base complexes of Cu(II), Co(II), Zn(II) and VO(IV) containing 4-(4-aminophenyl)morpholine derivatives: antimicrobial evaluation and anticancer studies, Spectrochim. Acta, Part A 117 (2014) 87e94. [17] A.K. Burat, A. Koca, J.P. Lewtak, D.T. Gryko, Preparation, electrochemistry and optical properties of unsymmetrical phthalocyanines bearing morpholine and tert-butylphenoxy substituents, Synth. Met. 161 (2011) 1537e1545. [18] A. Kilic, E. Tas, B. Gumgum, I. Yilmaz, Synthesis, spectroscopic and electrochemical investigations of two vic-dioximes and their mononuclear Ni(II), Cu(II) and Co(II) metal complexes containing morpholine group, Chin. J. Chem. 24 (2006) 1599e1604. [19] L.R. Rocha, E. D’Elia, R.A. Mederios, C.R.T. Tarley, Electroanalytical determination of morpholine as a corrosion inhibitor at a cathodically pretreated boron-doped diamond electrode, Anal. Lett. 52 (2018) 1083e1096. [20] Ü. Demirbas¸, D. Akyüz, H.T. Akçay, A. Koca, E. Mentes¸e, H. Kantekin, Novel 1,2,4-triazole substituted metallo-phthalocyanines: synthesis, characterization and investigation of electrochemical and spectroelectrochemical properties, J. Mol. Struct. 1173 (2018) 205e212. lu, A. Koca, H. Kantekin, Synthesis, character[21] V. Çakır, F. Demir, Z. Bıyıklıog ization, electrochemical and spectroelectrochemical properties of metal-free and metallophthalocyanines bearing electropolymerizable dimethylamine groups, Dyes Pigments 98 (2013) 414e421. _ Yalçın, H. Yanık, H.T. Akçay, I. _ Deg irmenciog lu, M. Durmus¸, Photophysical [22] I. and photochemical study on the tetra 4-isopropylbenzyloxy substituted phthalocyanines, J. Lumin. 192 (2017) 739e744. €ksel, M. Durmus¸, Z. Bıyıklıog lu, Synthesis and photo[23] V. Çakır, M. Go physicochemical properties of novel water soluble phthalocyanines, Dyes Pigments 125 (2016) 414e425. _ Deg irmenciog lu, Azine-bridged [24] R. Bayrak, H.T. Akçay, M. Pis¸kin, M. Durmus¸, I. binuclear metallophthalocyanines functioning photophysical and photochemical-responsive, Dyes Pigments 95 (2012) 330e337. _ Deg irmenciog lu, R. Bayrak, M. Er, K. Serbest, New olefinic centred binuclear [25] I. clamshell type phthalocyanines: design, synthesis, structural characterisation, the stability and the change in the electron cloud at olefine-based symmetrical diphthalonitrile fragment by the combined application of UVeVis electronic structure and theoretical methods, Polyhedron 30 (2011) 1628e1636. mus¸, [26] A. Günsel, A.T. Bilgiçli, B. Tüzün, H. Pis¸kin, G.Y. Atmaca, A. Erdog M.N. Yarasir, Synthesis of tetra-substituted phthalocyanines bearing 2-(ethyl(m-tolyl)amino)ethanol: computational and photophysicochemical studies, J. Photochem. Photobiol., A 373 (2019) 77e86. € rdük, A. Altindal, Peripherally tetra-substituted metallophthalocyanines [27] S. Go bearing carboxylic acid groups for efficient dye sensitized solar cells, J. Mol. Struct. 1196 (2019) 747e753. [28] R.Z.U. Kobak, D. Akyüz, A. Koca, Substituent effects to the electrochromic behaviors of electropolymerized metallophthalocyanine thin films, J. Solid State Chem. 20 (2016) 1311e1321. € lam, A.R. Ozkaya, [29] S. Arucu, M.B. Sag Electrochemical, spectroelectrochemical and electrocatalytic properties of newly synthesized phthalocyanine com0 pounds with 1,1 -thiobis(2-naphthol) groups, J. Mol. Struct. 1198 (2019), 126883. [30] T. Keles¸, D. Akyüz, Z. Biyiklioglu, A. Koca, Electropolymerization of
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BODIPY dyes bearing polymerizable substituents, Inorg. Chim. Acta 466 (2017) 130e138. [32] J. Tarver, J.E. Yoo, Y.-L. Loo, Organic electronic devices with water-dispersible conducting polymers, Compr. Nanosci. Technol. (2011) 413e446.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Electrochemistry, electropolymerization and electrochromism of novel phthalocyanines bearing morpholine groups Duygu Akyüz a, b, Ümit Demirbas¸ c, *, Atıf Koca a, Fatih Çelik c, Halit Kantekin c _ Department of Chemical Engineering, Engineering Faculty, Marmara University, Istanbul, Turkey Department of Chemistry, Faculty of Science, Gebze Technical University, Kocaeli, Turkey c Department of Chemistry, Faculty of Science, Karadeniz Technical University, Trabzon, Turkey a
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 October 2019 Received in revised form 28 December 2019 Accepted 30 December 2019 Available online 3 January 2020
In this work, 4-(4-((4-morpholinophenylimino)methyl)phenoxy)phthalonitrile (3) and it’s peripherally tetra substituted metal-free (4), zinc(II) (5), copper(II) (6) and nickel(II) (7) phthalocyanines were synthesized for the first time. The structural characterization of these novel compounds were performed with FT-IR, 1H NMR, 13C NMR, UVeVis and mass spectroscopy. Electrochemical and spectroelectrochemical characterizations of phthalocyanines (4e7) showed that while all phthalocyanines went to characteristics phthalocyanine ring and/or metal based reduction processes during the negative potential scans, all complexes were coated on the working electrode during the oxidation processes due to the cationic electropolymerizations of the 4-(4-((4-morpholinophenylimino)methyl)phenoxy) substituents. Changing the metal centers of phthalocyanine ring influenced the redox processes due to the different redox activities and effective nuclear charges of the metal centers. In addition to the electropolymerization ability of 4-(4-((4-morpholinophenylimino)methyl)phenoxy) substituent slightly affected the reversibility and peak positions of the redox processes. Indium tin oxide coated glass electrode (ITO) was coated with electropolymerized films of phthalocyanines to construct ITO/PolyPhthalocyanine and these electrodes were tested as a potential electrochromic material. ITO/PolyPhthalocyanine provided color change between green and blue with 1.2 s switching time, 18% optical contrast and 100% optical stability with 50 cronoamperometric (CA) cycles. These studies indicated possible usage of the electropolymerized films of phthalocyanines as possible building blocks for advanced electrochromic devices needing green-blue color change. © 2020 Elsevier B.V. All rights reserved.
Keywords: Morpholine Metallo-phthalocyanines Electrochemistry Spectroelectrochemistry (Oxidative) electropolymerization
1. Introduction Since their discovery, phthalocyanines (Pcs) have been important compounds for scientists. Phthalocyanines are aromatic heterocyclic compounds consisting of isoiminoindole moieties [1]. Phthalocyanine ring has a strong electron delocalization. This 18 p electronic conjugation imparts significant thermal, photo and electrochemical properties to Pcs [2]. Thanks to these features phthalocyanines can be used in many different applications such as solar cells [3], chemical sensors [4e6], liquid crystals [7], non-linear optics [8], laser dyes [9], catalyst [10], photo-voltaic optics [11], optical storage devices [12] and semiconductors [13]. Morpholines are six-membered ring compounds containing
* Corresponding author. E-mail address: [email protected] (Ü. Demirbas¸). https://doi.org/10.1016/j.molstruc.2019.127674 0022-2860/© 2020 Elsevier B.V. All rights reserved.
nitrogen and oxygen atoms. Thanks to their biological and pharmacological features morpholines can be used in many applications such as tyrosinase inhibitory [14], antioxidant [15], antiinflammatory [16]. In addition, electrochemical features of morpholines are significant. There are many studies in the literature that containing morpholine substituted compounds are used in electrochemical applications [17e19]. In this study, we have intended to synthesize 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituted phthalocyanines and investigate their electrochemical and spectroelectrochemical properties for the first time. Their electrochemical responses were determined in order to enhance the redox worth and to facilitate the medications of electrodes with electropolymerization of the phthalocyanines.
2
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
2. Experimental The used equipments, materials and synthesis were given as supplementary materials in detail. 2.1. Electrochemical, in-situ spectroelectrochemical and electrocolorimetric measurements Cyclic voltammetric (CV), square wave voltammetric (SWV) and in-situ spectroelectrochemical (SEC) measurements were carried out according to following procedure [20]. Glassy carbon electrode
(GCE) used as working electrode with electrode surface area of 0.071 cm2 for all voltammetric measurements. The platinum wire and silver-silver chloride (Ag׀AgCl) electrode were employed as counter, and reference electrode, respectively in voltammetric measurements. Measurements were carried out in dichloro methane (DCM) containing tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte at a concentration of 0.10 mol/ dm3 under pure nitrogen atmosphere. In situ SEC and electrocolorimetric (EC) measurements were carried out in homemade quartz cell by using a Reference 600 Gamry potentiostat and QE65000 OceanOptics diode array spectrophotometer. Indium tin
Scheme 1. Synthetic route for novel compounds (3e7).
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
3
oxide (ITO) glass electrode (surface area of 0.80 cm2), a platinum wire counter and a silver-silver chloride (Ag׀AgCl) reference electrode were used for the SEC measurements. SEC and EC measurements were carried out in ultra pure water (18 mU, milipore) solution including LiClO4 at concentration 0.10 mol/dm3. 2.2. Electrode modification with electropolymerization Electropolymerization technique was employed for the electrode modification by following paper [21]. For the formation of ITO/Poly-Pcs, Pc solution was electropolymerized on the ITO surface with repetitive 10 CVs in the electrochemical cell containing 5.0 104 mol dm3 Pc in DCM solution. CV scans were performed between 1.50 and 0.50 V at 100 mV s1 scan rate on ITO electrode. The non-electropolymerized Pc species were removed from the ITO/Poly-Pc electrode by washing with DCM and water respectively and finally it was dried in an oven under atmospheric conditions at 25 C. 3. Results and discussion 3.1. Synthesis and characterization The synthesis of novel compounds (3e7) was displayed in Scheme 1. The compound (3) was prepared with the reaction between 4-((4-morpholinophenylimino)methyl)phenol (1) and 4nitrophthalonitrile (2). In the IR spectrum, the new vibrations were observed at 2232 cm1 and the 13C NMR signals appeared at 115.891 and 112.456 ppm showed that compound (3) has nitrile (-C^N) groups. In the 1H NMR spectrum the new aromatic protons demonstrated that phthalonitrile (3) was successfully prepared. In NMR spectra aromatic and aliphatic protons and carbon signals showed expected values. The [MþH]þ mass peak confirmed the structure of compound (3). All characterization data are in accordance with the literature about the substituted phthalonitriles [22,23]. The novel phthalocyanines (4e7) were prepared with a cyclotetramerization reaction of phthalonitrile compound (3) in npentanol. They were characterizated by a combination of FT-IR, 1H NMR, UveVis and mass spectral data. The completion of cyclotetramerization reaction was confirmed by the disappearance of eC^N vibrations in the IR spectra of phthalocyanines (4e7). In addition, the vibrations were shown at 3290 cm1 in the IR spectrum of metal-free phthalocyanine (4) was confirmed the proposed structure of compound. Aromatic and aliphatic protons demonstrated expected signals in the 1H NMR spectra of compound (4, 5 and 7). In addition, because of the presence of paramagnetic copper(II) ions the 1H NMR measurements of compounds (6) could not be performed [24]. On the other hand the inner core protons of compound (4) could not be observed in the 1H NMR spectrum due to the strong aggregation between phthalocyanine molecules [25]. The observed [M]þ and [MþH]þ peaks in the mass spectra
Table 1 Voltammetric data of the complexes in DCM solutions. All data were given versus AgǀAgCl. Complexes
a
E1/2 of Redox couples
Oxd. of substituents H2Pc (4) ZnPc (5) CuPc (6) NiPc (7) a
1.15 e 1.12 1.13
Oxd1
Red1
Red2
0.60 0.57 0.57 0.56
0.55 0.83 0.71 0.75
0.84 1.21 0.98 1.05
Fig. 1. a) CVs and b) SWVs of H2Pc (5.0 104 mol dm3) recorded at various scan rates and on a GCE electrode in DCM/TBAP.
Fig. 2. Repetitive CV of H2Pc (5.0 104 mol dm3) recorded at 100 mVs1 scan rate on a GCE in DCM/TBAP.
confirmed the structures of compounds (4e7). The UVeVis spectra of compounds (4e7) were as expected. All characterization data are in accordance with the literature about the phthalocyanines [26,27]. 3.2. Voltammetric measurements
0.94 0.98 0.94 0.96
E1/2 values (Epa þ Epc)/2) were recorded at 100 mV s1 scan rate.
Voltammetric analyses of Pcs (4e7) bearing tetra 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent were carried out with CV and SWV in DCM/TBAP electrolyte on GCE working electrode. The basic electrochemical parameters were derived from
4
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the voltammograms and they were tabulated in Table 1. As shown in Table 1, while all complexes show clear Pc based reduction peaks during the cathodic potential scans, they were electropolymerized during the anodic potential scans. Fig. 1 represents CVs and SWVs of H2Pc (4). H2Pc (4) illustrates two reversible reduction processes at negative potentials at 0.55 V and 0.84 V, which are assigned to [H2Pc2]/[H2Pc3]1and [H2Pc3]1-/[H2Pc4]2- couples. During the positive potential scans, the Pc oxidation process of [H2Pc2]/[H2Pc1]1þ at 0.60 V is followed with a huge substituent oxidation wave at 1.08 V. 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent have polymerization ability, thus their possible electropolymerization process is carried out with repetitive CV measurements, which is represented in Fig. 2. As shown in this figure, during the first CV cycle, the oxidation waves of the 4-(4-((4-morpholinophenylimino) methyl)phenoxy) substituent are observed at 0.94 and 1.15 V. Due to the polymerization of the cationic species created during the oxidation process, the oxidation waves of the polymer are observed at 0.90 and 1.12 V during the second CV cycle. These new waves and their corresponding reduction couple increase in current intensity with small potential shifts with respect to increasing CV cycle numbers. Until 40 CV cycles, two quasi-reversible couple is observed for the electropolymerized film on the electrode surface. These voltammetric responses illustrate formation of a redox active and conductive poly-[H2Pc2] film on GCE surface with cationic electropolymerization of 4-(4-((4-morpholinophenylimino) methyl)phenoxy) substituent of [H2Pc2]. Electrochemical behaviour of H2Pc is consistent with literature. It is reported that H2Pc gives two reduction reaction and one oxidation reaction in the result of the electrochemical characterization [28,29]. The ligands
including morpholine groups generally polymerize during the oxidation reaction. For example, metallo-phthalocyanine complex including 5-{[(1E)-(4-morpholin-4-ylphenyl)methylene]amino}-1naphthoxy substituent was electropolymerized on GCE [30]. Z. Biyiklioglu and et al. synthesized BODIPY dyes containing 4morpholin-4-yl-benzyl and 4-(dimethylamino)-1-naphthyl and they electropolymerized on working electrode [31]. Changing the Hþ center of Pc ring with Zn2þ, Cu2þ and Ni2þ cations slightly decrease the reversibility of the reduction processes with negative potential shifting due to the changing of the effective nuclear charge of the cations in the core of Pc ring. All of these complexes give two Pc based reductions and one Pc based oxidation processes in addition to the oxidation waves of 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent. Fig. 3 shows CVs and SWVs of NiPc (7) as an example. Reduction peaks of NiPc (7) are observed at 0.75 V for [NiPc2]/[NiPc3]1and 1.06 V for [NiPc3]1-/[NiPc4]2- couples. [NiPc2]/[NiPc3]1-
Fig. 3. a) CVs and b) SWVs of NiPc(5.0 104 mol dm3) recorded at various scan rates on a GCE in DCM/TBAP.
Fig. 4. Repetitive CV of a) CuPc, b) ZnPc, and c) NiPc(5.0 104 mol dm3) recorded at 100 mVs1 scan rate on a GCE in DCM/TBAP.
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
couple at is followed with the oxidation waves of substituents at 0.96 and 1.20 V. As shown in Fig. 4c, NiPc (7) is also electropolymerized due to the cationic polymerization of the cations of 4(4-((4-morpholinophenylimino)methyl)phenoxy) substituents. CuPc (6), ZnPc (5) and NiPc (7) illustrates similar electropolymerization features with small changes, which is stem from effect of metal center, as shown in Fig. 4. Generally, two oxidation waves are observed for the electropolymerized films of all complexes, but due to the siftings of the first oxidation wave, these oxidation peaks are overlapped and form a broad wave with increasing CV cycles. As shown in Table 1, CuPc (6) and ZnPc (5) complexes give similar voltammetric responses with slight changes on the redox potentials. Electrochemical responses of CuPc (6) and ZnPc (7) are given in Fig. S1 and Fig. S2. 3.3. Spectroelectrochemical and electrocolorimetric measurements To illustrate electrochromic responses of Pcs (4e7) spectroelectrochemical and electrochemical measurements were performed in LiClO4/H2O electrolyte. Electrochromic electrodes were prepared by electropolymerizations of Pcs (4e7) on ITO electrodes and then ITO/Poly-Pcs were tested as possible electrochromic materials. All complexes (4e7) illustrated similar responses thus
5
electrochromic measurements results of ITO/Poly-NiPc are shown in Fig. 5. Transmittance changes of ITO/Poly-NiPc electrode under applied potential is given in Fig. 5a. The neutral ITO/Poly-NiPc electrode gives three bands at 443, 638 and 685 nm which are the characteristic bands of NiPc (7). When 1.50 V was applied to the working electrode, while the existence bands increase in T% intensity, the region at around 550 nm decreases. These spectral changes cause to a color change from green to blue. In order to investigate electrochromic parameters, repetitive CA excitations were employed between 0.0 V and 1.50 V with 30 s intervals. During CA measurements, ‘T% versus time’ and ‘Current (I) versus time’ responses were measured. As shown in Fig. 5b, symmetric anodic and cathodic currents were observed for each CA cycle and coulombic stability decrease as 34% within 50 CA excitations. In order to determine optical stability, response time, and optical contrasts, T% -time changes were also measured at 680 nm during the CA excitations. As shown in Fig. 5c, difference between maximum and minimum T% values give the optical contrast as 18% and the optical contrast keeps its stability with in the 50 CA cycles. Response times are measured as 1.20 s and 4.20 s for anodic and cathodic color changes respectively at 680 nm. The color efficiency (h) that is one of important parameter in electrochromic materials, and is calculated according to the following equation [32]
Fig. 5. a) SEC (T% vs. wavelength changes) measurement, b) CA responses of ITO/Poly-NiPc electrode between Eapp ¼ 0.00 V (time ¼ 30 s) and Eapp ¼ 1.50 V (time ¼ 30 s) c) T% versus time responses of ITO/Poly-NiPcin LiClO4/H2O electrolyte system.
6
h¼
D. Akyüz et al. / Journal of Molecular Structure 1206 (2020) 127674
DOD Qd
(1)
where, DOD is the ratio of optical density contrast and Qd is to charge consumed per unit area (Qd) during an electrochromic transition by using CA measurement. It is calculated for ITO/PolyNiPc electrode and is estimated as 94.57 cm2C-1 for 680 nm. Electrochromic responses of CuPc (6) and ZnPc (7) are given in Fig. S3 and Fig. S4. 4. Conclusions In this study, 4-(4-((4-morpholinophenylimino)methyl)phenoxy)phthalonitrile (3) and it’s peripherally tetra substituted metal-free (4), zinc(II) (5), copper(II) (6) and nickel(II) (7) phthalocyanines were synthesized for the first time. The structural characterization of these novel compounds were performed with FT-IR, 1H NMR, 13C NMR, UVeVis and mass spectroscopy. Electrochemical measurements indicated that Pcs (4e7) illustrate very similar characteristic Pc ring based reduction and oxidation processes. All complexes illustrated two reduction reaction during the cathodic potential scans and they showed similar electropolymerization responses. Changing the metal centers only influenced reversibility and position of the redox couples. 4-(4-((4morpholinophenylimino)methyl)phenoxy) substituent triggered electropolymerization of the complexes during the oxidation reactions. Electropolymerized films illustrates electrochromic color changes between green and blue colors. Electrochromic efficiency of NiPc was observed considerably higher than those of ZnPc (5) and CuPc (6). CRediT authorship contribution statement Duygu Akyüz: Visualization, Writing - original draft, Writing review & editing, Investigation. Ümit Demirbas¸: Project administration, Visualization, Writing - original draft, Writing - review & editing, Resources, Investigation, Conceptualization. Atıf Koca: Visualization, Writing - original draft, Writing - review & editing, Resources, Investigation, Conceptualization. Fatih Çelik: Visualization, Writing - original draft, Writing - review & editing, Resources, Conceptualization. Halit Kantekin: Visualization, Writing - original draft, Writing - review & editing, Resources, Investigation, Conceptualization. Acknowledgements Atıf Koca thanks Turkish Academy of Sciences (TUBA) for support. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.127674. References [1] N.B. McKeown, Phthalocyanine Materials: Synthesis, Structure, and Function, Cambridge University Press, Cambridge, 1998. [2] A.L. Thomas, Phthalocyanine Research and Applications, CRC Press, Boca Raton, Florida, 1990. [3] F. Yang, S.R. Forrest, Photocurrent generation in nanostructured organic solar cells, ACS Nano 2 (2008) 1022e1032. [4] C.C. Leznoff, A.B.P. Lever, Phthalocyanines Properties and Applications, vol. 1, VCH Publisher, New York, 1989.
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