Synthesis And Spectral Properties Of Near-Infrared Heptamethine Cyanine Fluorescence Dyes With Thio Or Amino Substitution At The Central Position

Heptamethine cyanine dyes employed as fluorescence labels and sensors of biomolecules in vivo have attracted immense interest because their spectra reach the near-infrared (NIR) region, where a biological matrix exhibits the least absorption and autofluorescence background. Much research work has been carried out with the aim of improving their photostability and spectral properties.A new heptamethine indocyanine dye with good photostability and water-solubility was synthesized in this thesis. Then a series of derivative dyes were obtained by an apparent nucleophilic reaction at the central chlorine atom of the parent dye. The synthesis and spectral properties of these derivative dyes are the main part of the thesis. A great improvement in dyes' Stokes shift (from 25 nm to 140 nm) is the most important innovation to the NIR heptamethine cyanine dyes.Two benzyl groups were introduced to the two N atoms at the two 3H-indo rings of the new heptamethine cyanine dye respectively. Compared with another dye with N-ethyl group, the new parent dye was found better photostability, which indicates that N-benzyl group can improve photostability for its rigid and bulk structure. In additional, it is found that dyes in water solutions are easier to photo-bleach than in alcohol solutions. A reasonable mechanism was proposed to explain the phenomenon. The reaction condition of the parent dye was improved by replacing benzene by toluene as the solvent. The parent dye was purified by recrystalling in water easily for derivative reactions.Four new dyes with thio group substitution in the central position were synthesized from the parent dye by nucleophilic substitution reaction. Photoinduced electron transfer (PET) was found to exist between the substituents and the fluorophore. Moreover, PET can be tuned by changing the electron-donating ability of the substituents. This effect is seldom seen for near-infrared fluorescent dyes. Among these derivative dyes, a dye with4-aminophenylthio-substitution exhibits the most efficient PET and the lowest fluorescence quantum yield. The acetylation, protonation or transition metal cation coordination of the amino group can recover fluorescence greatly via suppressing the PET. This result suggests that it is feasible to design MR fluorescence cation probe based on this kind of heptamethine cyanine dyes.Five derivative dyes from the parent dyes were obtained by similar nucleophilic substitution reaction in which five primary amines were employed as the nucleophilic reagent. Some particular spectral properties were found in the new dyes. Three of these dyes with alkyl secondary amino group at the central position were found to exhibit a large Stokes shift (>140 nm) and strong fluorescence. They were suggested to be a new paradigm for excited-state intramolecular charge transfer (ICT). The configuration change of the bridgehead amine accompanying ICT was investigated in different viscosity and pH media.To clarify the mechanism of the excited state of dyes with amino group, two more dyes in which alkyl tertiary amino replaces the chlorine atom were prepared from the parent dye. The two new dyes also possess a large Stokes shift, which can exclude one possible mechanism of excited-state intermolecular proton transfer.Finally, the photostabilities of these derivative dyes were investigated. Those dyes with good photostabilities were found to have poor fluorescence. It is attributed to the strong electron-donating ability of their substituents at the central position. An efficient PET may be easy to take place in those dyes, which make them photostable and no fluorescence at the same time.