Halogen atoms induced reversible supramolecular assembly and pH-response of the fluorescence properties: Low driving force triggered fluorescence switch with high SNR and high stability

Study on the modulating effect of halogen atom substitution on the detection range of water content detection probes in organic solvents

Fluorescence probes based on the variations of aggregation state (Aggregation-Induced Emission (AIE) and Aggregation-Caused Quenching (ACQ)) have received widespread attention due to their simplicity, efficiency and intuitiveness. However, typical probes are highly sensitive to changes in polarity and slight variations in the external environment can cause a complete change in the aggregation state. With the aim of expanding the detection range of the molecular probe, this work adopts a different design strategy from adjusting the molecular backbone but regulates the fluorescence behavior of the Schiff base molecular backbone by introducing different halogen atoms. Systematic studies show that when chlorine serves as substitutional atoms (3,5-Cl Salen), the probe can achieve full-range detection of water content (0-100 vol%) in ethanol and DMF. To our knowledge, the 3,5-Cl Salen represents the best water content probe in organic molecules. Experimental and theoretical studies have shown that the adjustment of halogen atoms can linearly change the charge distribution on the benzene ring and precisely control the strength of intermolecular interactions. At the same time, we developed a fluorescent filter paper based on 3,5-Cl Salen and used smartphones for rapid, sensitive and precise on-site measurement of water content in organic solvents.

Supramolecular Dimer as High-Performance pH Probe: Study on the Fluorescence Properties of Halogenated Ligands in Rigid Schiff Base Complex

The development of high-performance fluorescence probes has been an active area of research. In the present work, two new pH sensors Zn-3,5-Cl-saldmpn and Zn-3,5-Br-saldmpn based on a halogenated Schiff ligand (3,5-Cl-saldmpn = N, N'-(3,3'-dipropyhnethylamine) bis (3,5-chlorosalicylidene)) with linearity and a high signal-to-noise ratio were developed. Analyses revealed an exponential intensification in their fluorescence emission and a discernible chromatic shift upon pH increase from 5.0 to 7.0. The sensors could retain over 95% of their initial signal amplitude after 20 operational cycles, demonstrating excellent stability and reversibility. To elucidate their unique fluorescence response, a non-halogenated analog was introduced for comparison. The structural and optical characterization suggested that the introduction of halogen atoms can create additional interaction pathways between adjacent molecules and enhance the strength of the interaction, which not only improves the signal-to-noise ratio but also forms a long-range interaction process in the formation of the aggregation state, thus enhancing the response range. Meanwhile, the above proposed mechanism was also verified by theoretical calculations.

Crystal structure of 2-chloro-6-formylphenolato-κ2O,O′-(6,6′-(((2,2-dimethylpropane-1,3-diyl)bis(azaneylylidene))bis(methaneylylidene))bis(2-chlorophenolato)κ4 N,N,O,O′)cobalt(III), C26H22Cl3CoN2O4

C26H22Cl3CoN2O4, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 11.1835(5) Å, b = 11.6782(5) Å, c = 11.9295(5) Å, α = 83.900(3)°, β = 66.911(4)°, γ = 64.232(4)°, V = 1286.83(11) Å3, Z = 2, R gt (F) = 0375, wR ref (F 2) = 0.0899, T = 213.0 K.