Synthesis And Properties Investigation Of Condensed Heterocyclic Aldehyde Thiosemicarbazone Schiff Bases

Heterocyclic compounds have been widely used in the field of π-conjugated materials, optoelectronic devices, dyes and other areas owing to its large conjugated system, high chemical stability and the emission wavelength can be changed by modification of the structure. The sulfur atom and nitrogen atom in the thiosemicarbazone have strong complexation ability, and can be used in the synthesis and design of the fluorescent probe. This paper mainly use benzo quinoxalin fused heterocyclic as fluorescent chromophores, the sulfur and nitrogen atoms in thiosemicarbazide as identify atomic designed and synthesized a kind of benzo quinoxalin Schiff base fluorescent probes. There structures were characterized and the optical properties were investigated. The main research results description as follows:1. Two Schiff base fluorescence probes were synthesized successfully by condensation reaction between 5,5’-（acenaphtho[1,2-b]quinoxaline-8,11-diyl）dithiophene-2-carbaldehyde, 5,5’-（acenaphtho[1,2-b]quinoxaline-8,11-diyl）difuran-2-carbaldehyde and thiosemicarbazone. Probe M1 and M2 could be used as a fluorescent probe for the detection of Hg²⁺. M1 and M2 have strong orange red fluorescence originally, the obvious fluorescence quenching could be observed when Hg²⁺ added. Optical properties of M1 and M2 were scarcely affected by the addition of other common background metal ions under the same condition. The detection limit of M1 and M2 to Hg²⁺ reaches 6.79×10^-7 M and 5.81×10^-7 M, respectively.2. A Schiff base fluorescent probe M3 was synthesized through condensation reaction between 4,4’-（9a,13a-dihydrodibenzo[a,c]phenazine-10,13-diyl）dibenzaldehyde and thiosemicarbazide. We found that M3 possessed aggregation-induced emission enhancement（AIEE） properties, when water as a poor solvent for M3 was used at a fraction above 60 %, an intense fluorescence enhancement was observed. When the fraction of water in co-solvent up to 70 %, the emission intensity reaches 2.44-fold higher than that in pure DMSO. M3 could be used as a fluorescent probe for the detection of Hg²⁺. Accordingly, the solution after added Hg²⁺ demonstrated a clear color change from yellow-green to light red. Other coexisting ions have no interference with M3 for the detection of Hg²⁺. The detection limit of Hg²⁺ was 9.07×10^-7 M.3. The optical properties of the synthesized M1, M2 and M3 were further studied, and it was found that M1, M2, M3 could be used as PA fluorescence probes. M1, M2 itself has a strong orange red fluorescence and M3 has a yellow green fluorescence, when PA added, the fluorescence of M1, M2, M3 are completely quenched. Other coexisting nitro compounds have no effect on the probe M1, M2 and M3. The detection limit is 1.18×10^-7 M, 1.13 ×10^-7 M and 1.09 ×10^-7 M.