A rhodamine based fluorescent trivalent sensor (Fe3+, Al3+, Cr3+) with potential applications for live cell imaging and combinational logic circuits and memory devices

A sensor (HL5) based on rhodamine 6G-en and 3-(3,5-dimethyl-pyrazol-1-ylmethyl)-2-hydroxy-5methyl- benzaldehyde (HL4) has been developed for a highly sensitive and selective CHEF based recognition of trivalent metal ions M3+ (M = Al, Fe and Cr) over mono(-) and di-valent and other biologically abundant trivalent metal ions with prominent enhancement in absorption and emission intensities. A large enhancement of fluorescence intensities for Fe3+ (21 fold), Al3+ (14 fold) and Cr3+ (10 fold) was observed upon addition of 1.8 equivalents of these metals into the probe in methanol/H2O (1 : 1, v/v, pH 7.2) with the possibility of naked eye detection. The corresponding K-f values were evaluated to be 6.7 x 10(4) M-1 (Fe3+); 8.2 x 10(4) M-1 (Al3+) and 6.0 x 104 M-1 (Cr3+). The quantum yields of HL5 and [HL5-Fe3+] and [HL5-Cr3+] and [HL5-Al3+] complexes in methanol/H2O (1 : 1, v/v, pH 7.2) are found to be 0.013, 0.290, 0.120, and 0.158, respectively, using rhodamine-6G as the standard. The LOD for Fe3+, Al3+ and Cr3+ were determined by 3 sigma methods with values 0.29, 0.34 and 0.31 mu M, respectively. An arsenate ion snatches Al from the Al-HL5 complex and quenches its fluorescence via its ring closed spirolactam form. Advanced level molecular logic devices using the inputs 2 and 4 and memory devices, have been constructed. The low cytotoxicity and large enhancement in fluorescence intensity of HL5 upon complexation with M3+ metal ions make the probe suitable for bio-imaging of M3+ (M = Al, Fe and Cr) in living cells and native cellular iron pools.