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

With the unique properties of hydrogen bonding donor and hydrogen bondacceptor, squaramides have been widely used in biological field, optical materials,drug design, chiral catalysis, molecular recognition and so on. We have synthesizedtwo unknown squaramides122and123, as well as a squaraine124which have notbeen reported so far. Their structures have been characterized by IR,1H NMR,13CNMR and MS; and the properties have been studied by means of absorption andemission spectra. The main results are summarized as follows:(1) From commercially available N-methyl aniline (130), squaramide122hasbeen synthesized successfully through nucleophilic addition and aminolysis reaction.From commercially available aniline (132),3-[4-(dibutylamino)phenyl]-4-hydroxy-cyclobut-3-ene-1,2-dione (134) has been synthesized successfully throughnucleophilic addition and condensation reaction. Squaraine123has been synthesizedsuccessfully through the condensation of squaramide122and3-[4-(dibutylamino)phenyl]-4-hydroxycyclobut-3-ene-1,2-dione (134). The yield of123in thecondensation procedure is24.3%.We have studied the absorption and emission properties of122and123. Theabsorption and emission spectra of122show two absorption peaks around250nmand290nm with strong absorption coefficients (ε>104) and no fluorescene emission.The absorption spectrum of123shows a strong peak around640nm and a weak peakaround260nm, possibly belonging to the absorptions of squaraine moiety andsquaramide moiety, respectively. Due to the effect of hydrogen bonding, theabsorption of squaramide123in short wave band has a slight blue-shift comparingwith122. The flexibility chains at squramide moiety of123results in the fluorescenceintensity decreased.Due to the nature of electron-deficient at squaraine ring,123was easily sufferednucleophilic attack, leading to fading. Upon the additon of primary amine, themaximum absorption peak of123decreased, having a potential applications in thedetection of primary amine. (2) From commercially available adamantane (139), N-(2-adamantyl)aniline (142)has been synthesized successfully through oxidation and reductive amination.Squaraine124has been synthesized successfully through the condensation of aniline142and squaric acid (127). The yield of124in the condensation procedure is35.3%.As we know,124is the first reported squaraine with NH connecting directly withfour-membered squaric acid ring.The optical properties of124has been investigated. Because of the influence ofweak hydrogen bonds and the rigid adamantyl side chains, the absorption of124has a15nm blue-shift in various solvents compared with its analogs without NHs such as137and138. In the TFA titration experiments,124showed a red-shift first and then ablue-shift. At last a banch of relatively strong wide peaks around500-600nmemerged.Affected by hydrogen bonding, the solubility of124in water is higher than thatof137and138, showing a much weaker aggregaiton compared to137and138.Furthermore，because the adamantane’s skeleton structure matches the cavity size ofβ-cyclodextrin (β-CD),124and β-CD can form relatively stable inclusion complexes.Due to the steric protection of the β-CD, the aggregation of the complexes wereinhibited.