A novel rhodamine-based colorimetric chemodosimeter for the rapid detection of Al³⁺ in aqueous methanol: Fluorescent 'OFF-ON' mechanism

A novel rhodamine-based chemosensor, 3′,6′-bis(diethylamino)-2- ((2,7-dimethoxy-9H-fluoren-9-ylidene)amino)spiro[isoindoline-1,9′-xanthen] -3-one (1) for aluminum ion, was designed and synthesized. Compound 1 is an orange colored, weak fluorescent compound which was synthesized via one-step facile reaction of rhodamine B hydrazide with 2,7-dimethoxy-9H-fluoren-9-one in MeOH. When Al³⁺ salt was added in methanol:water (30:70, v/v) solution then spirolactum ring of 1 was opened. The absorbance and fluorescence of the mixed solution were increased dramatically because of the opening of the lactum ring. Thus, signal transduction occurred via reversible CHEF (chelation-enhanced fluorescence) mechanism in the range 580-584 nm.