Electrooxidation of rhodamine B hydrazide

Abstract

Spirocyclic rhodamines are promising sensors that exhibit turn-on fluorescence response to different stimuli including electric potential. Although rhodamine B hydrazide is often used as a building block for chemical and electrochemical sensors, the electrochemistry of this compound has not been reported. Herein, the electrochemical transformations of rhodamine B hydrazide are investigated using a combination of spectroelectrochemistry, liquid chromatography/mass spectrometry, and fluorescence spectroscopy. Pure rhodamine B hydrazide is a spirocyclic compound that is neither colored nor fluorescent. The electrooxidation of rhodamine B hydrazide in acetonitrile is shown to produce rhodamine B, a phtalazinone derivative, and a phenanthrenone derivative. These compounds exhibit fluorescence bands peaked at 580, 645, and 770 nm, respectively. The electrooxidation mechanism probably involves diazo, diazonium, and acylium intermediates. These findings imply a variety of applications for rhodamine B hydrazide as an electric potential sensor.