A ratiometric fluorescent chemosensor for iron: discrimination of Fe2+ and Fe3+ and living cell applicationElectronic supplementary information (ESI) available. CCDC reference numbers 651981. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2an35258c

A newly designed probe, 6-thiophen-2-yl-5,6-dihydrobenzo[4,5]imidazo-[1,2-c] quinazoline ( HL 1 ) behaves as a highly selective ratiometric fluorescent sensor for Fe 2+ at pH 4.0-5.0 and Fe 3+ at pH 6.5-8.0 in acetonitrile-HEPES buffer (1/4) (v/v) medium. A decrease in fluorescence at 412 nm and increase in fluorescence at 472 nm with an isoemissive point at 436 nm with the addition of Fe 2+ salt solution is due to the formation of mononuclear Fe 2+ complex [Fe II (HL)(ClO 4 ) 2 (CH 3 CN) 2 ] ( 1 ) in acetonitrile-HEPES buffer (100 mM, 1/4, v/v) at pH 4.5 and a decrease in fluorescence at 412 nm and increase in fluorescence at 482 nm with an isoemissive point at 445 nm during titration by Fe 3+ salt due to the formation of binary Fe 3+ complex, [Fe III (L) 2 (ClO 4 )(H 2 O)] ( 2 ) with co-solvent at biological pH 7.4 have been established. Binding constants ( K a ) in the solution state were calculated to be 3.88 × 10 5 M −1 for Fe 2+ and 0.21 × 10 3 M −1/2 for Fe 3+ and ratiometric detection limits for Fe 2+ and Fe 3+ were found to be 2.0 μM and 3.5 μM, respectively. The probe is a "naked eye" chemosensor for two states of iron. Theoretical calculations were studied to establish the configurations of probe-iron complexes. The sensor is efficient for detecting Fe 3+ in vitro by developing a good image of the biological organelles. A 6-thiophen-2-yl-5,6-dihydrobenzo[4,5]imidazo-[1,2- c ]quinazolineprobe probe that can discriminate between two Fe( ii / iii ) oxidation states is reported. The probe can detect iron in both abiotic and cellular systems.