Formation of static anthracene excimers at hydrophobic phosphate surfaces

Abstract

9-Anthracenemethylammonium chloride (AMAC) binds to layered zirconium phosphate in the presence of butylamine, with a high affinity. The electronic absorption and emission spectra of the anthryl chromophore change dramatically upon binding to the layered phosphate and provide spectroscopic signatures for the microenvironment. Upon binding, new excimer-like emission was observed around 440 nm over a narrow concentration range of AMAC. The appearance of the excimer emission critically depended upon the concentrations of both the phosphate and the anthryl chromophore. Addition of sodium chloride inhibits the excimer formation indicating the role of electrostatic interactions in the binding of the chromophore. Quenching of AMAC fluorescence by iodide anion shows that the excimer-like emission is protected from the quencher and supports the hypothesis that the excimer is formed at the negatively charged phosphate surfaces. Excimer emission was not observed when AMAC binds to DNA or to polyelectrolytes. Thus, binding to the layered phosphates can induce excimer formation even from the short-lived singlet excited state of the anthryl chromophore.