The absorption and fluorescence spectra of a new styryl derivative of thioflavin T 2-(1E,3E)-4-[4-(dimethylamino)-2,6-dimethylphenyl]buta-1,3-dien-1-yl-3-ethyl-1,3-benzothiazol-3-ium tosylate (Th-C23) in solvents with different polarity and viscosity and also incorporated in the structure of amyloid fibrils and bovine serum albumin were investigated. A characteristic feature of the dye is an extremely low quantum yield of fluorescence in low-viscosity solvents (10–4 in water) which, however, increases significantly in viscous solutions and when it is incorporated in the structure of proteins or amyloid fibrils. In the latter case the quantum yield increases by 8∙103 times. On the basis of the experimental studies and quantum chemical calculations it was shown that Th-C23 exhibits the properties of a molecular rotor. The increase of the fluorescence quantum yield in viscous solutions and in the biopolymers results from limitation of the torsional rotation of the molecular fragments, leading to fluorescence quenching. The long-wavelength location of the absorption spectrum and the fluorescence spectrum of the new dye in the red region of the spectrum (520 and 600 nm) makes it possible to use it as a fluorescent marker that is sensitive to the viscosity (hardness) of the microenvironment not only in vitro but also in vivo.

Spectral properties of an indotricarbocyanine dye upon complex formation with nanodiamonds in aqueous medium were studied. Complex formation is accompanied by the disappearance of the H*-aggregated band at 514 nm as well as by a bathochromic shift of the electronic absorption peak from 706 to 718 nm. At the same time, the emission spectrum of the dye is almost unchanged, and the fluorescence excitation peak is shifted from 706 to 710 nm. Based on the analysis of IR absorption spectra, it was found that carboxyl groups in the dye molecules play an important role in the complex formation of the dye with nanodiamonds. In the presence of human blood serum, complexes break down and dye molecules bind to serum proteins, which is confirmed by a significant increase in the lifetime and fluorescence anisotropy. The complexes obtained can be used as a basis of fluorescent biosensors.

Self-assembly of H*- and J-aggregates of an indotricarbocyanine dye in phosphate buffered saline was investigated. At pH value of 7.0 the dye studied was shown to form non-luminescent H*-aggregates with the absorption band peaked at 516 nm, its FWHM being 35 nm (1303 cm-1), whereas, J-aggregates are absent. At pH value of 7.4 the H*-aggregates are not formed, whereas, the J-aggregates are observed. The absorption band of the J-aggregates is peaked at 777 nm, its FWHM being 30 nm (497 cm-1). Photoluminescence quantum yield of the J-aggregates does not exceed 10-6. An increase in the solution temperature from 20 to 31oC results in a 25-fold decrease in the self-assembly time of the H*-aggregates. An increase in the solution temperature from 20 to 80oC is followed by a reversible decay of both the H*- and J-aggregates. The H*-aggregate (J-aggregate) absorption band is reduced two-fold at the solution temperature of 37oC (32oC). Thansitions of the dye aggregates to high-lying electronic excited states were evidenced in the steady-state absorption in the spectral range between 400 and 480 nm.

The effect of the vacuum annealing temperature on the structure and functional composition of the surface of ultradispersed diamond (UDD) produced by detonation synthesis was studied using Raman scattering, IR absorption, X-ray diffraction analysis and electron paramagnetic resonance. It was established that vacuum annealing at T ≤750°C does not affect the structure of diamond nanoparticles; at higher annealing temperatures, the formation of amorphous sp 2 -hybridized carbon begins on the surface of the particles. Annealing at a temperature of 1050°С leads to complete graphitization of the UDD surface with preservation of the diamond structure of the nucleus of the particles. During annealing in the temperature range of 650-750°C, the minimum of functional groups is observed on the UDD surface, while the surface retains high activity.

The spectral properties of a novel thioflavin T derivative, trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT), were studied in aqueous solutions in the presence of sodium polystyrene sulfonate (SPS). It was shown that SPS either could interact with dye monomers or initiate the formation of non-fluorescent dye dimers depending on the concentration ratio of dye and polyelectrolyte. DMASEBT dimer formation in the presence of SPS produced a hypsochromic shift by 40 nm in the absorption spectrum and quenched fluorescence. A bathochromic shift of the absorption spectrum and an increase of the fluorescence intensity by an order of magnitude were observed if DMASEBT monomers interacted with SPS. Quantum-chemical analysis found that sandwich dimers (H-aggregates) were most stable. A comparison of DMASEBT spectra in the presence of SPS and amyloid fibrils showed that DMASEBT molecules were incorporated into amyloid fibrils as monomers. The spectral changes associated with this incorporation could not be explained by the formation of dye aggregates.

Spectral properties of a newly synthesized thiofl avin T (ThT) derivative, trans-2-[4-(dimethylamino)styryl]-3-ethyl-1,3-benzothiazolium perchlorate (DMASEBT) with absorption and fluorescence spectra shifted to longer wavelengths (than ThT), were studied. Quantum-chemical calculations established that DMASEBT is planar in the ground state. The energy minimum of the excited molecule corresponded to a twisted conformation (TICT-state) with a 90° angle between the planar fragments. Charge in the molecule redistributed and a non-fluorescing TICT-state was formed if the fragments rotated. Fluorescence occurred from the non-equilibrium excited state (LE-state). It was shown that limited torsional rotation of the molecular fragments and; therefore, a decreased probability of transitioning into the non-fluorescing TICT-state, were responsible for the significantly increased quantum yield and fluorescence lifetime of DMASEBT upon increasing the solvent viscosity and incorporating it into amyloid fibrils.