Фотоуправляемые обратимые изменения электронных и колебательных спектров фотохромного диарилэтена в различных наноструктурированных системах

An analysis of the results of complex experimental and theoretical studies of photoinduced changes in the spectral properties of photochromic diarylethene in various nanostructured systems is presented. The properties of diarylethene were studied in solutions in the presence of colloidal metal and semiconductor nanoparticles, as well as in the form of solid-phase composite nanostructured core-shell systems based on colloidal nanoparticles with a shell of diarylethene molecules (including in a polymer matrix). A photoinduced reversible change in the electronic and vibrational spectra of diarylethene in various studied matrices was found. The results can be used to create optoelectronic photo-switchable elements for ultra-high-capacity memory devices, photo-controlled molecular switches and sensors.

Revealing momentum-dependent electron–phonon and phonon–phonon coupling in complex materials with ultrafast electron diffuse scattering

Despite their fundamental role in determining many important properties of materials, detailed momentum-dependent information on the strength of electron–phonon and phonon–phonon coupling across the entire Brillouin zone has remained elusive. Ultrafast electron diffuse scattering (UEDS) is a recently developed technique that is making a significant contribution to these questions. Here, we describe both the UEDS methodology and the information content of ultrafast, photoinduced changes in phonon-diffuse scattering from single-crystal materials. We present results obtained from Ni, WSe2, and TiSe2, materials that are characterized by a complex interplay between electronic (charge, spin) and lattice degrees of freedom. We demonstrate the power of this technique by unraveling carrier–phonon and phonon–phonon interactions in both momentum and time and following nonequilibrium phonon dynamics in detail on ultrafast time scales. By combining ab initio calculations with ultrafast diffuse electron scattering, insights into electronic and magnetic dynamics that impact UEDS indirectly can also be obtained. Graphic Abstract

Effect of Cu2O Substrate on Photoinduced Hydrophilicity of TiO2 and ZnO Nanocoatings

The effect of a Cu2O substrate on the photoinduced alteration of the hydrophilicity of TiO2 and ZnO surfaces was studied. It was demonstrated that the formation of heterostructures Cu2O/TiO2 and Cu2O/ZnO strongly changed the direction of the photoinduced alteration of surface hydrophilicity: while both TiO2 and ZnO demonstrate surface transition to superhydrophilic state under UV irradiation and no significant alteration of the surface hydrophilicity under visible light irradiation, the formation of Cu2O/TiO2 and Cu2O/ZnO heterostructures resulted in photoinduced decay of the surface hydrophilicity caused by both UV and visible light irradiation. All observed photoinduced changes of the surface hydrophilicity were compared and analyzed in terms of photoinduced alteration of the surface free energy and its polar and dispersive components. Alteration of the photoinduced hydrophilic behavior of TiO2 and ZnO surfaces caused by formation of the corresponding heterostructures with Cu2O are explained within the mechanism of electron transfer and increasing of the electron concentration on the TiO2 and ZnO surfaces.

Using Photoactive N-Heterocyclic Carbenes Monolayers to Identify the Influence of Surface Proximity on Photoswitching Activity

<p>Self-assembly of photoresponsive molecules is a robust technology for reversibly tuning the chemical and electronic properties of functional materials. In most systems the photoactive group is separated from the surface by a spacer and thus the photo-responsiveness does not benefit from interactions with the metal. Herein, the impact of metal photoactive-group interactions on photoswitchability and surface potential were probed by self-assembly of N-heterocyclic carbene molecules (NHCs) that were functionalized with stilbene group directly on their imidazole ring. Stilbene-NHCs that were adsorbed on weakly interacting Au surface accumulated a vertical orientation, as identified by FTIR measurements. This positioning enabled structural flexibility and high photoisomerization efficiency that induced reversible changes in surface potential. Stilbene-NHCs that were anchored on Pt film accumulated flat-lying adsorption geometry due to strong metal-adsorbate interactions. These interactions limited the structural flexibility of the stilbene groups and induced deteriorated photoswitchability that led to lower photoinduced changes in surface potential. While stronger metal-adsorbate interactions hindered the photo-induced isomerization yield of stilbene, these interactions prompted the <i>cis</i>-to-<i>trans</i> thermal-induced isomerization rate, which was an order of magnitude higher on Pt than on Au. </p>

Using Photoactive N-Heterocyclic Carbenes Monolayers to Identify the Influence of Surface Proximity on Photoswitching Activity

<p>Self-assembly of photoresponsive molecules is a robust technology for reversibly tuning the chemical and electronic properties of functional materials. In most systems the photoactive group is separated from the surface by a spacer and thus the photo-responsiveness does not benefit from interactions with the metal. Herein, the impact of metal photoactive-group interactions on photoswitchability and surface potential were probed by self-assembly of N-heterocyclic carbene molecules (NHCs) that were functionalized with stilbene group directly on their imidazole ring. Stilbene-NHCs that were adsorbed on weakly interacting Au surface accumulated a vertical orientation, as identified by FTIR measurements. This positioning enabled structural flexibility and high photoisomerization efficiency that induced reversible changes in surface potential. Stilbene-NHCs that were anchored on Pt film accumulated flat-lying adsorption geometry due to strong metal-adsorbate interactions. These interactions limited the structural flexibility of the stilbene groups and induced deteriorated photoswitchability that led to lower photoinduced changes in surface potential. While stronger metal-adsorbate interactions hindered the photo-induced isomerization yield of stilbene, these interactions prompted the <i>cis</i>-to-<i>trans</i> thermal-induced isomerization rate, which was an order of magnitude higher on Pt than on Au. </p>

IR Photoinduced Piezoelectric Effects in Multi-Component Chalcogenides Ag2In(Ga)2Si(Ge)S(Se)6

The influence of external irradiation of CO2, CO, Er:glass, Nd:YA lasers on the piezoelectric properties of the Ag2In(Ga)2Si(Ge)S(Se)6 crystals was investigated. The maximum photoinduced changes in the piezoelectric coefficient were observed after irradiation with CO2 laser. CO photoinducing bicolour beams with 5.5 μm wavelength cause at least 4 times smaller increase in piezoelectric coefficients. Therefore, it can be expected that the primary mechanisms cause the excitation of the phonon subsystem.

SYNTHESIS AND PHOTOVOLTAIC PROPERTIES OF SYMMETRIC BIS-AZOMETHINES WITH ACCEPTOR SUBSTITUENTS IN THE 4,4'-POSITION

Two new symmetric azomethine dyes capable of photoinduced isomerization were synthesized by condensing symmetric bis-aldehyde (obtained by the reaction of epichlorohydrin with 4-oxybenzaldehyde) with 4-nitroaniline and 4-chloroaniline, respectively. The yield of the target products decreases with the transition from nitro-substituted azomethine to chlorine-substituted. This is due to the greater basicity of the starting amines with nitro-substitution when increasing the acceptor force of the substituent complicates the course of the reaction. Azomethines are characterized by absorption with a maximum at 400–410 nm, which makes them sensitive to radiation with a blue component of the spectrum. The photoelectric properties of azomethines upon irradiation were investigated by the method of measuring the surface potential with the help of a Kelvin dynamic probe. The maximum value of the electric potential of the photosensitive films free surface during irradiation with white LED at I = 60 W/m2 is about 270 mV in the case of azomethine with a nitro group in the 4,4' position and about 125 mV in the case of azomethine with chlorine as a substituent. That is, the magnitude of the electric potential of the free surface decreases approximately twice during the transition from nitro substituent to chlorine. This may be explained by the fact that the photoinduced changes in azomethine with a higher acceptor substituent flow more quickly and with greater efficiency. But at the same time, the reverse changes when turning off the light are just as fast. For chlorine substituted azomethine samples, the reverse process proceeds rather slowly, which may indicate greater stability over time of the photochemically modified form in case of chlorine substitution compared to the nitro-substituted analogue. Thus, the synthesized azomethines can be used in the development of new photovoltaic media and recording media for optical information recording.

Влияние ультрафиолетового облучения на деформационные свойства синдиотактического 1,2-полибутадиена: роль окисления

We studied the impact of ultraviolet (UV) irradiation on stress–strain characteristics, derived from uniaxial stretching measurements, and the molecular structure (photoinduced changes) of syndiotactic 1,2-polybutadien, a polymer with thermoplastic elastomer properties. Uniaxial stretching stress–strain curves are recorded for samples subjected to UV irradiation for different times and the effects UV irradiation has on the stress–strain behavior of polymers are analyzed. Long UV irradiation is found to markedly increase the hardening of polymers: Young’s modulus and yield strength increase, while the fracture strain decreases. At the same time, we observe a sharp increase in polymer molecular weight and its considerable oxidation that particularly involves surface layers. The mechanisms of cross-linking between macromolecules and their simultaneous oxidation induced by exposure to UV light are discussed along with the role these processes play in evolution of the physical mechanical properties under UV irradiation.