Four new derivatives of 8-aminoquinolines are successfully synthesized by extension of the p-conjugated system on the quinoline ring and incorporation of either the salicylaldimine or its reduced amino form. These compounds show selective fluorescence enhancement by Zn 2 + ion, attributing to the chelation-enhanced fluorescence (CHEF) effects, in which the deprotonation of the amido -NH and phenolic -OH causes the internal charge transfer (ICT) process. The fluorescent signals of these compounds are shifted from the range of 391-562 nm to 535-590 nm upon addition of Zn 2 + . The sensing mechanism is investigated by 1 H NMR titration, mass spectrometry, and single crystal X-ray diffraction analysis which suggests a 1:1 binding stoichiometry between the sensor and Zn 2 + . The detection limits of 0.024 to 0.431 mM and the association constants ranging between 7.0 3 10 3 and 1.2 3 10 4 M À1 can be estimated for these four sensors. One of these compounds is fabricated on wax-patterned filter paper and used as a probe for Zn 2 + in aqueous solution with a naked-eye detection limit at 10 mM.The zinc ion is the second most abundant transition metal ions in living organism after iron. It plays crucial roles in many important biological processes like structural and catalytic cofactors, neural signal transmitters or modulators, and regulator of gene expression and apoptosis. [1] Moreover, it is known that a disorder of zinc metabolism is closely associated with many severe neurological diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease, hypoxia-ischemia, and epilepsy. [2] In the environment, an excessive concentration of zinc may reduce the soil microbial activity resulting in a phytotoxic effect. [3] The development of detection methods for zinc ion such as inductively coupled plasma mass spectroscopy, [4] atomic absorption spectroscopy, [5] gel electrophoresis, [6] and reverse-phase liquid chromatography have been widely reported. [7] Nevertheless, these techniques rely on expensive instruments, complicated procedures, and skillful users. Fluorescence spectroscopy has then become a preferred method of choice due to its high sensitivity and selectivity with simple instrument operation. A number of fluorescent sensors based on various fluorophores such as quinolone, [8] fluorescein, [9] coumarin, [10] naphthalimide, [11] BODI-PY, [12] and others were developed for detection of zinc ions. [13] However, the development of new zinc-selective fluorescent sensors with high affinity and good selectivity over other relevant metal ions, especially Cd 2 + is still highly desirable.During our work on the development of new fluorescent chemosensors, we recently became interested in the sensing properties of 8-aminoquinoline derivatives, especially their highly selective binding with glucosamine and several transition metals. [14] They have been used as ionophores for detection of Zn 2 + , [8b,15] and other metal ions such as Cu 2 + , Al 3 + , Cr 3 + , and Hg 2 + . [8c,d,16]...