Titanyl phthalocyanines: Electrochemical and spectroelectrochemical characterizations and electrochemical metal ion sensor applications of Langmuir films

https://doi.org/10.1016/j.jelechem.2013.05.012Get rights and content

Highlights

  • Electrochemical and spectroelectrochemical characterizations of newly synthesized titanyl phthalocyanines.

  • Effects of position and number of substituents to the electrochemical behaviors.

  • Langmuir Blodgett monolayer film formation and characterization.

  • ITO/TiOPc + SA(LB) electrode as an electrochemical receptor element for various transition metal ions.

Abstract

Electrochemical and spectroelectrochemical characterizations of titanyl phthalocyanines, which were peripheral (α-TiOPc) and nonperipheral (β-TiOPc) tetra and octa substituted (octa-TiOPc) with 3,4-(methylendioxy)-phenoxy moieties were performed to determine their possible applications in different electrochemical technologies. Voltammetric and in situ spectroelectrochemical measurements illustrate that position and number of 3,4-(methylendioxy)-phenoxy substituents affect the redox behavior of the complexes. While α-TiOPc gives up to four reduction processes, β-TiOPc and octa-TiOPc gives up to three reduction processes. While octa-TiOPc gives metal–metal–ring–ring reductions, α-TiOPc and β-TiOPc complexes give metal–ring–ring–metal reduction mechanism. Solvent of the media also alter the electrochemical behavior of the complexes. In situ electrocolorimetric measurements shows distinct color differences among the electrogenerated anionic and cationic redox species, which indicates their possible applications in display technologies. Multiple and reversible, diffusion controlled and multi-electron redox reaction indicate possible usage of the complexes especially in electrosensing applications. The complexes sense Ag+ and Pd2+ ions in the solution and in the solid states.

Introduction

Phthalocyanine (Pc) complexes are of great interest due to their various important applications in modern science and technology such as photodynamic therapy, chemical sensors, non-linear optics, liquid crystals [1], [2], [3], [4], [5]. Their semi-conducting properties are exploited for applications such as photoconductors [6], solar cells [7] as well as gas sensors [8] and their electrochemical properties [9], [10] are utilized for electrochemical applications such as electrocatalytic [11], [12], electrosensing [13], [14] and electrochromic fields [15]. Various phthalocyanines have been investigated for the relevant applications. Although all transition metals can coordinate to Pc ligands, only a few of them (Zn, Ti, Pd) can form highly photoactive complexes, such as titanyl phthalocyanine (TiOPc), owing to the closed shell nature of the electronic configuration of Ti4+, similar to that of main group metal ions [16], [17], [18]. Although TiOPc have found many more important applications in especially high sensitive photoconductors in laser printing and photocopying, now a days, the studies are condensed to the sensor applications of TiOPc complexes [8]. In our previous papers, we reported electrochemical properties and electrocatalytic activities of various TiOPc complexes [19], [20], [21]. However the related studies for the electrochemical application of TiOPc and its derivatives are still rare in the literature [19], [20], [21], [22], [23], [24], and the correlation of electrochemical properties with their chemical structures is much less explored compared to the case of other MPcs. In literature, Nyokong and her coworkers [22], [23] and our research group have studies on the electrochemistry and electrochemical applications of TiOPcs. On the basis of our previous reports on the electrochemical, electropolymerization, electrochromic, electrosensing, and electrocatalytic properties of MPcs [19], [20], [21], [25], [26], [27], [28], [29], we now extend our studies with the synthesis, characterization and application studies of TiOPcs and their derivatives. Thus in this paper, we have investigated the electrochemical and spectroelectrochemical properties of TiOPc synthesized and published by our research group [29] (Scheme 1). We have also performed detailed investigation for the possible sensor and electroelectrocatalytic applications of TiOPc. It was found in this study that TiOPcs has potential to use as electrosensors for heavy metal ions.

Section snippets

Electrochemical and in situ spectroelectrochemical measurements

The cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements were carried out with Gamry Reference 600 potentiostat/galvanostat controlled by an external PC and utilizing a three-electrode configuration at 25 °C. The working electrode was a Pt disc with a surface area of 0.071 cm2. A Pt wire served as the counter electrode. Saturated calomel electrode (SCE) was employed as the reference electrode and separated from the bulk of the solution by a double bridge. Electrochemical grade

Voltammetric measurements

Electrochemical analyses of the complexes were investigated in solution to propose possible applications of the complexes in electrochemical technologies. For this purpose, the CV and SWV of the complexes (25) were recorded in DCM and DMSO/TBAP electrolyte system on a Pt working electrode. Table 1 lists the assignments of the redox couples and estimated electrochemical parameters including the half-wave peak potentials (E1/2), ratio of anodic to cathodic peak currents (Ip,a/Ip,c), peak to peak

Conclusions

Electrochemical and spectroelectrochemical measurement of TiOPc complexes indicated that incorporation redox active metal centers, TiO into the phthalocyanine core extend the redox richness of the Pc ring with the reversible metal-based reduction couples in addition to the common Pc ring-based electron transfer processes. This expanded redox behavior of the complexes are the desired properties of the electrochemical applications, especially, electrocatalytic, electrochromic and electrosensing

Acknowledgement

We thank to The Turkish Academy of Sciences (TUBA) and TUBITAK (Project No.: 111T179) for financial supports.

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