SYNTHESIS AND ABSORPTION SPECTRA OF INDOTRICARBOCYANINE DYES WITH ELECTRON-DONATING GROUPS IN THE MESO-POSITION OF THE POLYMETHINE CHAIN

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.