Figure 1.

a) Fluorescence decrease of 1 μM coucage with 0–100 equiv. Cu²⁺, along with the subsequent increase following UV exposure (thick black trace). Inset: Emission at 479 nm vs. added Cu²⁺. b) Blue bars: the unchanged fluorescence of 1 μM coucage in the presence of 1 mM Na⁺, K⁺, Mg²⁺, Ca²⁺ and Zn²⁺ or 50 μM for others; Purple bars: quenched emission upon addition of 50 μM Cu²⁺; black bars: restored fluorescence after 4 min of UV exposure. All samples prepared in 10 mM Hepes buffer at pH 7.4 with 10% DMSO and excited at 430 nm.