Abstract
We reported the design and synthesis of a new type of metal-cation probes, 3-hydroxy-4-(1,4,7,10-tetraoxa-13-azacyclopentadec-13-ylmethyl)naphthalene-2-carbaldehyde (
1a
) and its single hydrogen-bond analogue 1-(1,4,7,10-tetraoxa-13-azacylopentadec-13-ylmethyl)-2-naphthol (
2a
), in which 1-aza-15-crown-5 ether in combination with the naphthol oxygen acts as a receptor, while the mechanism of excited-state intramolecular proton transfer (ESIPT) is exploited as a signal transducer. The association constant of (2.5±0.5)×10
4, (3.8±0.4)×10
4, (5.5±0.5)×10
3 and (1.2±0.3)×10
4
M
−1 for the formation of
1a
/Na
+,
1a
/Ca
2+,
2a
/Na
+ and
2a
/Ca
2+ complexes, respectively, in CH
3CN plus drastic fluorescence changes due to the fine-tuning of ESIPT reaction upon complexation, lead
1a
and
2a
to be highly sensitive fluorescent sensors. The results add a new class into the category of metal-cation probes, with the perspective of designing ESIPT systems capable of sensing bio-analytes.
Graphical Abstract