Ferrocene-based chromogenic and fluorogenic derivatives for hair dyeing applications

Abstract

A new ferrocene-isoniazid Schiff base has been designed and synthesized for application as a hair dye. In addition, two other Schiff bases of ferrocene with aminopyrene and rhodamine B hydrazide were synthesized, and the three compounds are named IFC, AFC, and RFC, respectively. All the resulting Schiff bases were characterized by NMR, HRMS, and their photophysical properties were further evaluated via UV-visible and fluorescence spectroscopy. We anticipated that the incorporation of ferrocenecarboxaldehyde—a well-known organometallic compound—alongside amino counterparts could yield potential non-oxidative hair dyes suitable for dyeing human hair in various colors. All three dyes are found to exhibit effective UV-protection performance, in addition to their durability observed through SEM (scanning electron microscopy), contact angle and confocal studies, which showed negligible effect on the hair surface even after dye removal by multiple washings. Furthermore, a cell viability assay on human embryonic kidney (HEK-293A) and mouse fibroblast (L929) cells showed that IFC exhibited excellent biocompatibility, supporting its safety for cosmetic applications in hair dyeing.