The dissertation is devoted to the development of convenient methods for the synthesis of heptamethinecyanine dyes based on indole, benzo[e]indole and benzo[cd]indole derivatives with functionalized polymethine chromophores. Functionalizations were carried out by introducing electron-donating and electron-withdrawing groups in both the meso-position of the polymethine chain and the nitrogen atom of heterocycles, as well as by inserting polymethylene bridge groups in the γ,γ′-positions of the polymethine chain. Furthermore, spectral and luminescent properties of the synthesized cyanine dyes were studied and characterized. Their potential applications as light energy transducers in biology, medicine, sensors and laser technology were investigated.
New methods for the synthesis of heptamethinecyanines based on the ketocyanine derivatives were developed. Dyes with substituents of different electronic nature in the meso-position were synthesized, including those that previously could not be obtained by the well-known SRN1 reaction. This novel approach also resulted in high yields of the desired dyes. One major advantage is that neither the bis-aldehydes nor their iminium derivatives were used as starting compounds. Therefore, only the quaternary salts of indole, benzo[e]indole, and benzo[cd]indole derivatives were used as starting materials, which significantly simplified the synthesis of the desired cyanine dyes.
Due to the preparation of a series of meso-substituted heptamethinecyanine dyes, it was possible to study the Fester-Dewar-Nott rule in the absorption spectra of tricarbocyanines for the first time. It was demonstrated that the introduction of electron-donating substituents in the meso-position of the polymethine chain allowed a hypsochromic shift of the absorption maxima by more than 150 nm, especially in the case of nitrogen-containing substituents. These effects were explained by the conjugation of the electron pair of nitrogen with the polymethine chromophore leading to an increased bond-length alternations and the change of electronic state of the corresponding dyes from polymethine to polyene.
An unusual effect was observed. A strong electron donor such as a methoxy group in the meso-position of the indoheptamethinecyanine dye with a trimethylene bridge group causes a bathochromic rather than a hypsochromic shift in the absorption spectra, in contrast to other typical donor substituents, as well as to the Fester-Dewar-Nott rule. Based on the calculations by DFT-B3LYP method, it was shown that this effect occurred due to steric hindrance. Consequently, the meso-methoxy group was forced to leave the polymethine chromophore plane, which weakened their conjugation. In this case the spectral properties were mainly determined by the negative inductive effect of the oxygen atom.
On the contrary, the introduction of electron-withdrawing substituents to the meso-position demonstrates a long-wave shift of the absorption maxima of heptamethinecyanines. However, compared to the donor substituents, electron-withdrawing groups had a smaller impact on the spectral properties of the synthesized tricarbocyanines with the bathochromic shifts of the maxima by no more than 86 nm.
The effects occurring in the fluorescence spectra of heptamethinecyanine dyes and their correlation with the Fester-Dewar-Nott rule were studied for the first time. It was shown that the electronic effects of substituents in the meso-position were significantly weaker in the excited state of dye molecules, as their fluorescence maxima were close to the ones of unsubstituted heptamethinecyanines. As a result, tricarbocyanines with electron-donor substituents had abnormally large Stokes shifts, up to 4443 cm-1, while dyes with electron-withdrawing groups had expectedly smaller ones, up to 916 cm-1. Using the DFT-B3LYP calculation method, the spatial structures of meso-pyrrolidine substituted dyes with trimethylene and dimethylene bridge groups were studied. The differences in their fluorescence spectra were explained.
