Search

An efficient synthesis of functionalized 3-acyl-2H-indazoles via visible-light-induced self-catalyzed energy transfer was developed. This method utilized a self-catalyzed energy transfer process between 2H-indazoles and a-keto acids, offering advantages like absence of photosensitizers, metal catalysts, and strong oxidants, broad substrate compatibility, and operational simplicity under mild conditions.

One Cd–Nd nanowheel [Cd8Nd4L8(OAc)8]·4OH (1, molecular sizes: 1.2 × 2.8 × 2.8 nm) was obtained by using one designed flexible Schiff base ligand containing eight coordination sites. The Schiff base ligand exhibits a hexadentate η1:η2:η1:η1:η2:η1:μ4coordination mode. The chromogenic Cd/L components are able to transfer energy to Nd(III), leading to the near-infrared (NIR) lanthanide emission of 1. The energy transfer efficiency (ηsens) is calculated to be 39.4%. 1shows interesting luminescent sensing activity toward metal cations and nitro-based explosives, in particular to Cu(II), Fe(III), Co(II), and 2,4,6-trinitrophenol (TNP) with high sensitivity. The quenching constants of the complex toward Cu(II), Fe(III), Co(II), and TNP respectively are 8.6 × 104, 6.8 × 104, 6.5 × 104, and 2.1 × 105M–1. The luminescent sensing of the nanowheel to metal cations is able to be explained by chelation enhancement of the quenching (CHEQ) effect, and its high selectivityto TNP is caused by the photoinduced electron transfer process and “inner filter effect”, even with the existence of other nitro-based explosives.

Two NIR luminescent Zn(II)/Cd(II)–Yb(III) complexes were obtained by the use of a Schiff base ligand with a binaphthyl backbone. Cd(II)–Yb(III) complex 2has a triangular structure and exhibits interesting luminescent sensing activity to antibiotics, in particular to ciprofloxacin (CPFX) and norfloxacin (NFX) due to the inner filter effect. The limits of the detection of 2to CPFX and NFX are 0.18 and 0.36 μM, respectively, and the fluorescence sensitivity is not changed with the existence of other antibiotics tested in this study.

Two d-4f complexes [Zn2NdL2(OAc)2]·OH (1) and [Cd3Sm3L3(OAc)6(OH)3] (2) with a designed Schiff base ligand N,N′-bis(3-methoxysalicylidene)(binaphthyl)-1,4-diamine (H2L) were synthesized. The Schiff base ligands coordinate with metal ions by μ2(η1:η2:η1:η1:η2:η1) and μ2(η1:η2:η1:η1:η2:η1) modes in the complexes, which show typical lanthanide emissions. The triangular Cd–Sm complex 2shows both visible and NIR luminescent responses to nitrobenzene explosive 2,4,6-trinitrophenol (PA).

One 12-metal Cd(II)–Yb(III) nanoring, [Cd8Yb4L8(OAc)8]·4OH (1), with a size of 1.2 × 2.8 × 2.8 nm was obtained from a designed flexible salen-type ligand that has eight coordination sites (O and N atoms). The near-IR emission of Yb(III) at 983 nm was detected upon the excitation of ligand-central absorption at 386 nm. This Cd(II)–Yb(III) nanoring exhibits high sensitivity to nitrofuran antibiotics (NFAs) even in the presence of other antibiotics. The quenching constants and limits of detection of NFAs are 2.5 × 104–4.5 × 104M–1and 1.5–2.8 μM, respectively.

One 18-metal Nd(III) nanoring, [Nd18(L1)8(HL2)2(OAc)20(MeOH)8(EtOH)6(H2O)4]·2(MeOH)·6(H2O) (1), was constructed by the use of a hexadentate Schiff base ligand. For 1, the near-infrared (NIR) luminescence of Nd(III) was detected under the excitation of absorption band at 371 nm. The study of luminescent sensing properties exhibits that, even with the existence of other antibiotics, this Nd(III) nanoring displays high sensitivity and selectivity to nitrofuran antibiotics (NFAs). The luminescence quenching constants and limits of detection of 1to NFAs are found to be 1.4 × 104to 3.5 × 104M–1and 0.9–2.2 μM, respectively.

One 14-metal Yb(III) nanoring [Yb14(HL)2L20(DMF)8(H2O)8] (1) with a size of about 1.1 × 2.5 × 2.7 nm was synthesized from a tridentate ligand. Under the excitation of ligand absorption bands, 1exhibits the NIR luminescence of Yb(III) and displays high luminescence sensitivity and selectivity to Co(II), Cu(II), and 2,4,6-trinitrophenol (PA) at the parts per million level. The KSVvalues of 1to Co(II), Cu(II), and PA are 6.0 × 104M–1, 3.8 × 104M–1, and 6.9 × 104M–1, respectively. 1exhibits high luminescent sensitivity to PA even in the presence of other explosives.