The electrochromic materials change their optical properties under the action of an electric field and can be change back to the initial state by a field reversal. This paper reports the use of two metalloporphyrins derivatives of; 5, 10, 15, 20-tetraphenyl 21H, 23H-porphine cobalt (II)(CoTPP) and 5, 10, 15, 20-tetraphenyl 21H, 23H-porphine manganese (III) chloride (MnTPPCl), Langmuir-Blodgett thin films as an electrochromic materials to detect the presence of chloride in water. It was found that the both thin films were sensitive towards the presence of chloride by presenting the change in their optical absorption spectrum under a bias potential of 3.0 V. However, the CoTPP thin film was not fully reproducibility under the electrochromic process. Meanwhile, the electrochromic property of the MnTPPCl thin film was stable and reproducible. This thin film is potentially be used as an electrochromic material to detect the presence of chloride ion in water.
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