Khodko A. Optical characteristics of photochromic diarylethene molecules and systems of photochromic molecules - nanoparticles.

This dissertation is devoted to the research of optical characteristics and cyclization dynamics of newly-modified photochromic molecules – furan-based diarylethenes with various functional substituents. To this purpose, an experimental setup of femtosecond transient absorption spectroscopy ("pump-probe") was modernized. A pumping system was created and implemented in a regime when each "pump" pulse irradiates the renewed volume of molecules. A measurement protocol has been developed to investigate the photochromic molecules in solutions. "Pump" initiated the cyclization reaction of diarylethenes, while "probe" tracked ultrafast changes in optical density. Since the cyclization reaction for studied diarylethenes occurs under UV illumination, the third harmonic generation (λ = 266 nm) was used as a "pump" and the supercontinuum generation (λ = 530 nm – 610 nm) was used as a "probe". The cyclization time constants for diarylethene derivatives with various functional substituents were obtained in the subpicosecond time range. Among the factors that minimize the duration of the cyclization process of diarylethene molecules are type of connection between the photochromic core and functional substituents and photochemical activity of the functional substituents. The time constant for diarylethene derivatives with acetyl-containing substituents is at least 0.2 ps, and it is the shortest optical response among the studied molecules. Also, UV-vis spectroscopy was used to study the optical characteristics of the systems of furan-based diarylethenes - gold nanoparticles. The effects of solvent polarity were studied and the optimal concentration of diarylethenes required to maintain the stability of the systems was defined. The influence of functional substituents on the processes of aggregation of gold nanoparticles in solutions was analyzed. Using transmission electron microscopy, it has been shown that diarylethenes with thiosemicarbazone substituents are characterized by the formation of four times larger aggregates of gold nanoparticles compared to methyl-thiosemicarbazone substituents, which is due to the more pronounced donor properties of thiosemicarbazone substituents. These results create a basis for the development of hybrid photosensitive composites with picosecond optical response, formed of furan-based diarylethenes with optimized structure and gold nanoparticles.