The Design, Synthesis And Properties Study Of New Squaraine-based Functional Compounds

Be a superior performance of near-infrared dyes, squaraines have received moreand more attention in recent years, and have been used for wide ranging applicationssuch as xerography, optical recording, photovoltaics, ion sensing, biological labeling,and low band gap polymers. Five new squaraines, which have not been reported so far,have been synthesized. Their structures have been characterized by IR,1H NMR,13CNMR, MS and HRMS; and their properties have been studied through absorption andemission spectrum. The main results are summarized as follow:1) Due to the unique highly symmetric structure and lipophilic nature of theadamantane, the introduction of adamantyl groups endow79a and79b some newproperties. Firstly, the existence of adamantyl group improves the solubility of thesquaraines in organic solutions, and by compared with1, the λmaxof79a and79b havesome red-shift. Secondly, the length of the methylene chain between the adamantylgroup and the nitrogen atom of the anilino group would affect the properties of thesquaraines. In the mixed HCOOH/H2O solution,79b had better solubility than79a,but contrary results were obtained in the pure organic solvent. Thirdly, the diameter ofthe adamantane’s skeleton structure is about0.7nm, which matches the cavity size ofβ-cyclodextrin (0.7~0.8nm), so the adamantane derivates and β-cyclodextrin canform relatively stable inclusion complexes. The binding constants are found to be8.3×104and2.7×104mol-2L2, respectively, for79a and79b with β-cyclodextrin.Squaraine dyes have propensity to form aggregates, which leads to substantialbroadening of their absorption bands and fluorescence quenching. The encapsulationof79a and79b into the β-cyclodextrin not only improves their solubility in water, butalso inhibits their aggregation in pure water solution due to the steric protection of theβ-cyclodextrin, and thus the fluorescence is retained. This provides a new approachfor designing water-soluble squaraines with strong fluorescence.2) Three cation sensors based on three different kinds of ionophores have beensynthesized; their optical properties and selectivity toward different metal ions have also been studied. Among of them,80is highly selective toward Hg2+in37:63H2O/AcOH (v:v) mixture, and the detection limit is down to4×10-7mol/L with C80=2μmol/L. The pilot studies shown that81and82had response to some metal ions, forexample, the presence of Ag+and Cu2+could lead to complete bleaching in the visiblerange and fluorescence quenching, while other metal ions had no response. Similar to81, addition of Ag+, Cu2+and Co2+could also lead82to bleaching in the absorptionspectrum and quenching of the fluorescence. But the absorption spectrum afterbleaching is different. In the presence of Cu2+, a new absorption band at586nmappears as long as the band at636nm.