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2 )] were performed in solution and in the solid states as Langmuir-Blodgett (LB) films. The type of the central metal of the complexes slightly altered the potentials of the electron transfer reactions. Redox peaks shifted toward the negative potentials as a function of the decreasing metal ion size. All complexes gave three reduction and one oxidation reactions with in the whole potential window of the electrolyte system. Due to the π-π interaction of phthalocyanine rings around the lanthanide metal ions the complexes were easily reduced at even positive potentials. Assignments of the redox processes, spectra and color of the electrogenerated species of the complexes were determined with in-situ spectroelectrochemical, and in-situ electrocolorimetric measurements. Various colors recorded during the electron transfer reactions well reflected electrochromic characters of the complexes. For practical usage, LB thin films of the complexes were easily coated on the ITO electrodes and investigated as electrochromic materials. All complexes displayed three distinctive color alternatives as green, orange, and red for their different redox states. Electrochromic measurements indicated that the nature of the metal ions in the phthalocyanine cavity alters the basic electrochromic parameters of the complexes. LB films of DyPc 2 and LuPc 2 were especially found as ideal neutral and anodic coloring electrochromic materials with their short response times, and high optical and coulombic stabilities.In addition to the wide range of the application fields, metallophthalocyanines (MPcs) have been extensively preferred in various electrochemical application technologies such as electrochromic, 1-3 semiconductor, 4,5 electrochemical sensor, 6-9 and electrocatalytic 10-12 applications because of their predominant electrochemical properties. 13,14 It is well known that basic electrochemical characterization of MPcs are directly related with the extensive π-electron delocalization of the Pc rings, redox activity of the central metals, and functionality of the substituent environments of the Pc ring. 15-17 Among phthalocyanine (Pc) derivatives, the syntheses of lanthanide (III) Pcs (LnPc 2 ) have attracted great attention due to the changing of the electrochemical responses of the complexes with the π-π interaction of the Pc rings of the sandwich complexes. 14,18-21 Altering the metal center and substituents of these type complexes easily affects their physical, electrical, optical, and electrochemical properties, 22-24 thus it is important to determine the electrochemical responses of the newly synthesized complexes to decide their possible application in different technologies. Therefore in this study, investigation of the electrochemical and spectroelectrochemical properties of a series of lanthanide (III) bis-phthalocyanines [samarium(III) (SmPc 2 ), europium (III) (EuPc 2 ), gadolinium (III) (GdPc 2 ), dysprosium(III) (DyPc 2 ) and lutetium(III) (LuPc 2 )] was aimed. The electrochromic features of the complexes were also examined...

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