PET fluoroionophores for Zn2+ and Cu2+: complexation and fluorescence behavior of anthracene derivatives having diethylamine, N-methylpiperazine and N,N-bis(2-picolyl)amine units

Abstract

Anthracene derivatives (1, 2) having one or two diethylamine (a), N-methyl-piperazine (b) and N,N-bis(2-dipicolyl)amine units (c) showed weak emission, suggesting that photoinduced electron transfer (PET) from the amine group to the excited anthracene occurs. The PET fluoroionophores (1, 2) were found to display unique photophysical properties in the presence of the guest metal salts. Complexation of diethylamine (1a, 2a) and N-methyl-piperazine derivatives (1b, 2b) with Ni²⁺, Cu²⁺ and Zn²⁺ enhanced the emission, while the emission intensities of N,N-bis(2-picolyl)amine derivatives (1c, 2c) are increased in the presence of Zn²⁺ and decreased in the presence of Ni²⁺ and Cu²⁺. The crystal structures of 2c and its zinc chloride complex showed that the binding of Zn²⁺ to the N,N-bis(2-picolyl)aminomethyl unit inhibits the photoinduced electron transfer process. Intramolecular π–π interactions between anthracene and the ZnCl₂-complexed pyridine were observed.