Synthesis and effect of substituent position, metal type on the electrochemical properties of (3-morpholin-4-ylpropoxy) groups substituted cobalt, manganese phthalocyanines

In this work, 4-(3-morpholin-4-ylpropoxy)phthalonitrile 2, 3-(3-morpholin-4-ylpropoxy)phthalonitrile 3, Co(II)Pc and Mn(III)Pcs containing (3-morpholin-4-ylpropoxy) groups at peripheral and nonperipheral positions were synthesized. Phthalonitrile derivatives (2 and 3), Co(II)Pc and Mn(III)Pcs (2a, 2b, 3a, 3b) were characterized by using FT-IR, NMR (only for 2 and 3), mass and UV–Vis (except 2 and 3) spectral data techniques. Also, electrochemistry of (3-morpholin-4-ylpropoxy) group substituted Co(II)Pc and Mn(III)Pcs were inspected by using cyclic voltammetry. Electrochemical studies show that (3-morpholin-4-ylpropoxy) group substituted Co(II)Pc and Mn(III)Pcs electropolymerized on the Pt working electrode.

Phthalocyanines bearing redox active metals (Co, Fe and Mn) have been investigated owing to their electrocatalytic properties [18]. The usage of cobalt phthalocyanines as an electrochemical sensor is of interest [19,20]. Also, Mn(III)Pcs exhibit exciting electrochemical response owing to different oxidation states of manganese ion [21]. In this work, we have synthesized Co(II)Pc and Mn(III)Pcs containing (3-morpholin-4ylpropoxy) groups at peripheral and nonperipheral positions. It has been found that the attachment of -(3morpholin-4-ylpropoxy) group to the phthalocyanine molecule in either a peripheral or nonperipheral position has a great effect on the electrochemical properties. * Correspondence: zekeriyab@ktu.edu.tr This work is licensed under a Creative Commons Attribution 4.0 International License.

Experimental design
All information about the used equipment, materials, synthesis, electrochemistry experiments is given in the Supplementary Information.

Electrochemical studies
The electrochemistry of Co(II)Pc and Mn(III) Pcs (2a, 2b, 3a, 3b) were obtained in DCM using a (DCM)/(TBAP) electrolyte system on a Pt working electrode. The electrochemical data were listed in Table. Figure  V for 3a) in DCM/TBAP electrolyte system. Co II can reduce before Pc ring, thus the R 1 process of 2a and 3a at E 1/2 = -0.39 V and -0.40 V is easily assigned to the Co II /Co I reduction reaction of the complexes [26]. Figure 5a and Figure 5b show the CV responses of 2b, 3b in DCM/TBAP electrolyte system. 2b and 3b exhibited 2 reduction labelled as R 1 (E 1/2 = -0.25 V for 2b, E 1/2 = -0.21 V for 3b) and R 2 (E 1/2 = -1.29 V for 2b, E 1/2 = -1.09 V for 3b) in DCM/TBAP electrolyte system. The first reduction can be assigned to [Cl-Mn III Pc −2 ] / [Cl-Mn II Pc −2 ] −1 because of the redox active manganese metal ion [27]. Then second reduction can be assigned to [Mn II Pc −2 ] / [Mn I Pc −2 ] −1 couple [28]. After first reduction, [Cl-Mn II Pc −2 ] −1 species release axial chloride ion. Similar results were appeared for Co(II)Pc and Mn(III)Pcs in literature [29,30].

While peripheral, nonperipheral tetra-(3-morpholin-4-ylpropoxy) group substituted Co(II)Pc and Mn(III)
Pcs (2a, 2b, 3a, 3b) illustrate widespread reduction reactions during the cathodic scans, Co(II)Pc and Mn(III)Pcs were electropolymerized on the working electrode during the anodic scans. Figure 6 shows the CV responses of peripheral, nonperipheral tetra-(3-morpholin-4-ylpropoxy) group substituted cobalt(II) phthalocyanines (2a and 3a) during repetitive CV cycles. When Figure 6a is examined, the onset oxidation potential of peripheral tetra-(3-morpholin-4-ylpropoxy) group substituted cobalt(II) phthalocyanine 2a at around 1.32 V is observed, whereas the onset potential of the nonperipheral tetra-(3-morpholin-4-ylpropoxy) group substituted cobalt(II) phthalocyanine 3a has been determined at around 1.36 V (Figure 6b). In the following cycles, the oxidation peak currents raised and there was a small shift in the oxidation peaks. This suggests that the Co(II)Pc and Mn(III)Pcs incur polymerization in each scan and deposit onto the electrode surface. Figure 7 shows the CV responses of peripheral, nonperipheral tetra-(3-morpholin-4-ylpropoxy) group substituted man-  ganese(III) chloride phthalocyanines (2b and 3b) during repetitive CV cycles. When Figure 7a is examined, the onset oxidation potential of peripheral tetra-(3-morpholin-4-ylpropoxy) group substituted manganese(III) chloride phthalocyanine 2b at around 1.38 V is observed, whereas the onset potential of the nonperipheral Table 1. Voltammetric data of the Pcs. All voltammetric data were given versus SCE.

Pcs
Oxidations Reductions