Syntheses And Properties Of Several Symmetrical Squarylium Bis-indocyanine Dyes

2,3,3–trimethyl–3H–indolin was synthesised by phenylhydrazine and3–methyl–2–butanone as raw materials in the acetic acid, and then was reacted with different nitrogenalkylating reagents and1,4–dibromo-butane to obtain mono-indoline-quaternary ammoniumsalts with three different substituents and dis-indoline-quaternary ammonium saltsrespectively. The two kinds of conducts acted with squaric diethyl ester respectively toprepare mono-semicynine dye and dis-semicyanine dye. Finaly, three kinds of symmetrcialsquarylium bis-indocyanine dyes with different substituents were synthesized withsemicyanine dye and indoline-quaternary ammonium salts. The products were purified usingnormal-phase silica gel column chromatograph.1H–NMR was used to characterize thestructure of products.The pectral properties of the dyes were tested in five different solvents, that include UVabsorption spectroscopy, fluorescence emission spectroscopy and photo-stability. The testingresults show that the dye exhibit maximum absorption in range of602⁶52nm, maximumemission from605to674nm. Their molar absorption coefficients is about10⁵mol^-1 cm^-1 Land Stokes shifts are in range of the3²2nm. Compared with other organic solvents, whenwas disssolved in water, the dye has the shortest maximum absorption wavelength, shortestmaximum emission wavelength and shortes Stokes shift and obvious aggregation.In proticsolvents, dye spectra show a blue shift with the increasing of solution polarity, while inaprotic solvents, dye spectral have a red shift with the increasing of solution polarity.In the same solvents, the stability order of bis-cyanine dyes is5a （N-p-carboxymethylbenzyl）>5f （N-p-chloro benzyl）>5c （N-ethyl）. The introduction of an electron withdrawinggroup on the nitrogen atom of the indole, the photo-stability of the dye can be enhanced. Indifferent solvents, the photo-stability of the dye in methanol is strongest.Compared with the corresponding mono-cyanine dyes, the bis-cyanine dyes havelonger Stokes shifts, a lower fluorescence quantum yield and better stability. Other properties,such as the variation of the spectrum of the dye in different solvents and the stability areconsistent with the mono-cyanine dyes.