Abstract
Recently, a large number of studies have been dedicated to chemistry and physical studies of polymethine dyes, especially to the functionalized symmetrical heptamethinecyanines based on the indole derivatives. Due to their unique and versatile spectral properties, which lie in the near infrared region (NIR), meso-substituted indotricarbocyanine dyes are widely used in various physical and biological fields. In the present work, we have developed methods of synthesis of a series of indotricarbocyanine dyes with di- and trimethylene bridging groups in the γ,γ'-positions and donor substituents in the meso-position of the polymethine chromophore and studied their effects on the spectral properties of the dyes. The obtained data indicated that the change of the substituent in the meso-position of the chromophore and the presence of a polymethylene bridging groups allow to vary significantly the absorption maxima of the synthesized indoheptamethinecyanine dyes without altering the length of the polymethine chain. It was shown that the electron-donating nitrogen-containing substituents lead, according to the Forster-Dewar-Knott rule, to a hypsochromic shifts of the absorption maxima. However, it was found that the methoxy group in the meso-position of the polymethine chromophore in some cases exhibited unexpected "acceptor" properties due to a certain steric hindrance, resulting in a red shift of the absorption band, in contrast to the other donor substituents. Additionally, the effects of the insertion of di- and trimethylene bridging groups to the polymethine chain of the cyanine dyes on their spectral properties were studied. The synthesized meso-substituted indotricarbocyanines demonstrated significant solvatochromism and spectral properties that lie in the red and near-infrared regions.
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