Synthesis And Optical Properties Of New Symmetrical Pentamethine Indocyanine Dyes

Cyanine dyes possess many good advantages such as easy to synthesize, proper fluorescence quantum yield. Cyanine dyes can be applied in biological yields.2,3,3–trimethyl–3H–indole was starting material. A series of N–alkyl–2,3,3– trimethyl– 3H–indolenine quaternaries were synthesized based on nucleophilic reaction of 2,3,3– trimethyl –3H–indole with appropriate N–alkyl reagents. A series of indocyanine dyes were synthesized by reaction of squaric acid and malonaldehyde dianilide hydrochloride with three equivalents of indolenine quaternaries. They were squarylium indocyanine dyes and chainlike pentamethine indocyanine dyes.These raw intermediates and products were purified by.recrystallization.Their structures were obtained by 1HNMR, FTIR and MS. Optical properties of dyes were studied in five different solvents the properties include UV absorption spectroscopy, fluorescence emission spectroscopy and photo- stability etal. The relationship between molecular structures and properties were investigated.The tests showed that: the maximum absorption wavelength of indocyanine dyes and the maximum emission wavelengths were in the near infrared region. Chainlike pentamethine indocyanine dyes have larger high the Stokes shift and lower values of fluorescence quantum yield in the aqueous compared with squarylium indocyanine dyes. Photostability tests showed that stability of squarylium indocyanine dyes were greater than the chainlike pentamethine indocyanine dyes.In the same solvents, the stability of cyanine dyes were on the order of(N-p- cyano benzyl) >(N-p-carboxy benzyl) > 5c(N- p-Methyl benzyl).The spectral properties of the dyes in two types of surfactants(CTAB, SDS) showed that: the change of spectral properties of the dyes in the cationic surfactant(CTAB) was obviously. With the micelle formation, UV absorption and fluorescence intensity increased significantly. Effect degree was related with structure of dyes, squarylium indocyanine dyes were lager than chainlike pentamethine indocyanine dyes. However, in the effect of anionic surfactant(SDS) on the dyes was not obviously.