Zinc(II)-Based Ring-and-Rod Coordination Layer as an Excitation-Wavelength-dependent Dual-Emissive Chemosensor for Discriminating Fe 3+ , Cr 3+ , and Al 3+ in Water.

The reactions of Zn(NO 3 ) 2 , 3,6- bis (pyridin-3-yl)-9 H -carbazole (bpycz), and 2,5-dihydroxyterephthalic acid (H 4 dhbdc) or 2-bromoterephthalic acid (Br-1,4-H 2 bdc) under hydro(solvo)thermal conditions yielded corresponding coordination polymers (CPs) {[Zn(H 2 dhbdc)(bpycz)]•0.5H 2 O} n ( 1 ) and [Zn(Br-1,4-bdc)(bpycz)]•2DMAc•H 2 O ( 2 ), respectively, with high thermal stability approaching 350 °C. CP 1 adopts a ring-and-rod layer structure, which is topologically described as a 4-connected net with the point symbol of 2•6 5 . Two layers are interpenetrated in parallel interlocking mode to form a double 2D → 2D polyrotaxane entanglement with extra-framework void space of 19.6%. CP 2 has a non-interpenetrating ring-and-rod layer structure of 4-connected 2•6 5 net topology, with extra-framework void space of 16.6%. Thermally activated 1 and 2 revealed CO 2 uptakes of 101.1 and 98.6 cm 3 g -1 , respectively, at P / P 0 = 1 and 195 K. X-ray powder diffraction (XRPD) patterns confirmed that 1 and 2 both possessed high chemical stability in H 2 O, CH 3 OH, acetone, and DMF, and framework stability during gas adsorption-desorption. The H 2 O suspension of 1 displayed excitation-dependent dual-emissive properties, appearing at 432 nm upon excitation at 300 nm and at 528 nm upon excitation at 365 nm. Of note, 1 was capable of detection of Fe 3+ , Cr 3+ , and Al 3+ ions in H 2 O, showing good anti-interference ability, excellent selectivity, and high sensitivity. More interesting, the dual-emissive properties make 1 to be an excellent luminescence chemosensor to screen Fe 3+ , Cr 3+ , and Al 3+ from a pool of metal ions in H 2 O upon excitation at 300 nm via luminescence quenching effect and then discriminate Fe 3+ , Cr 3+ , and Al 3+ upon excitation at 365 nm via luminescence quenching, unaltered, and enhancement responses, respectively. On the other hand, the H 2 O suspension of 2 demonstrated an excitation-independent emission appearing at around 430 nm, which could be utilized to sensitively detect Fe 3+ and Cr 3+ ions with good anti-interference ability and excellent selectivity via luminescence quenching effect. Further, 1 and 2 were recyclability and possessed cycling stability. The plausible sensing mechanisms for 1 and 2 toward Fe 3+ , Cr 3+ , and Al 3+ were also explored in detail.