Optical Anisotropy of Porphyrin Nanocrystals Modified by the Electrochemical Dissolution

Abstract

Reflectance anisotropy spectroscopy (RAS) coupled to an electrochemical cell represents a powerful tool to correlate changes in the surface optical anisotropy to changes in the electrochemical currents related to electrochemical reactions. The high sensitivity of RAS in the range of the absorption bands of organic systems, such as porphyrins, allows us to directly correlate the variations of the optical anisotropy signal to modifications in the solid-state aggregation of the porphyrin molecules. By combining in situ RAS to electrochemical techniques, we studied the case of vacuum-deposited porphyrin nanocrystals, which have been recently observed dissolving through electrochemical oxidation in diluted sulfuric acid. Specifically, we could identify the first stages of the morphological modifications of the nanocrystals, which we could attribute to the single-electron transfers involved in the oxidation reaction; in this sense, the simultaneous variation of the optical anisotropy with the electron transfer acts as a precursor of the dissolution process of porphyrin nanocrystals.

Experimental and Computational Aspects of Electrochemical Reflection Anisotropy Spectroscopy: A Review

“…Recently, the use of RAS in combination with AFM and CV has unraveled the mechanism responsible for porphyrin dissolution in acidic media, [95] a more complex system involving organic molecules. In their approach, several types of porphyrin nanocrystals were vacuum‐deposited on graphite substrates and cycled in sulfuric acid.…”