Background: Thin films of a 5,10,15,20-tetraphenylporphyrin (H2TPP) and its metal complexes (MeTPP, where Me = Co, Cu, Zn, Fe-Cl) were obtained by vacuum thermal evaporation under quasi-equilibrium conditions (hot wall method) and by coating from a toluene solution on various substrates. It was shown that H2TPP, CuTPP and CoTPP have an ability to selforganization into linear structures during crystallization (nanowhiskers, nanowires, or nanorods), regardless of our obtaining method. Methods: FeClTPP and ZnTPP crystallize into planar films with the same preparation technique. Co-deposition with fullerene C60 allows obtaining fullerene crystallites on the surface of tetraphenylporphyrin, subsequently creating the so-called bulk heterojunctions. Results: The possibility of controlling the shape of obtained crystallites by changing technological parameters and substrates has been shown for metal free tetraphenylporphyrin. High degree crystalline ZnTPP and H2TPP films are characterized by a red shift of photoluminescence and absorption spectra under crystallization. Conclusion: A change in the relative intensity of the photoluminescence spectrum maxima of various nature is observed during transition from amorphous to crystalline structure of H2TPP.

The absorption of exciting light by an inner filter may be the cause of large errors in estimating the efficiency of fluorescence quenching. We performed fluorescence measurements of 5,10,15,20-tetraphenylporphyrin toluene solution in a wide concentration range. We have shown a Förster-free fluorescence quenching in a right-angle geometry experiment, caused by second order inner filter. We proposed to perform measurements in a front-surface geometry to investigate the nature of quenching not related to the inner filters. We have shown that concentration effects in tetraphenylporphyrin solutions in toluene are not accompanied by a decrease in the fluorescence intensity in a front-surface geometry at concentrations of 10− 3-10− 7 mol/l. It was possible to separate the phenomena of the internal filters from the processes occurring in a liquid medium. Our results are of great importance due to the widespread fundamental research of porphyrin-based dyes properties. The Förster-free effect fluorescence is observed up to closed to the ultimate solubility concentrations in tetraphenylporphyrins toluene solution at concentrations of 10-3-10-7 mol/l. Förster radius was estimated for 5,10,15,20-tetraphenylporphyrin molecules. Concentration quenching of tetraphenylporphyrin solutions was studied in a wide range of concentrations. A correction experimental method is proposed conditions to minimize inner filter effects.

The investigation of the temperature effect on optical properties of porphyrins has tremendous impact for modern organic-based photonics and nanoelectronics. We performed temperature-dependent photoluminescence spectroscopy study of H2TPP, ZnTPP tetraphenylporphyrin-based thin films and their composites with C60 fullerene in the range of 77–370 K. The films under study were deposited by vacuum evaporation technique under quasi-equilibrium condition. We experimentally observed a monotonic temperature quenching for H2TPP and H2TPP-C60 films, and abnormal increase of luminescence intensity for ZnTPP and its composite at heating from 77 to 175 K. We suggest that this nonmonotonic behavior is associated with a charge carriers capture on the non-radiative-trapped centers. Further, we have estimated traps activation energy by the Arrhenius equation. Our results carry great importance in view of the widespread research on porphyrins with aim of their future industrial applications.

Photoluminescence temperature quenching of tetraphenylporphyrins thin films on silicon substrates have been investigated. Free-based tetraphenylporphyrin (H2TPP) and Zinc-tetraphenylporphyrin (ZnTPP) films were obtained by thermal evaporation in vacuum. The photoluminescence properties of these samples are observed in the wide temperature range from 77 to 300 K. The temperature-depended photoluminescence intensity of ZnTPP exhibits abnormal behaviour. An increase in the photoluminescence intensity is observed in the temperature range of 77-180 K. We suppose that charge carriers are trapped by non-radiative centres when the temperature decreases down to 77 K. The release of carriers occurs with a further temperature increase. In addition, there are sharp increases in the luminescence intensity of thin H2TPP and ZnTPP films at a temperature of 270 K, which are associated with a second-order phase transition.

The surface morphology of tetraphenylporphyrin thin polycrystalline films – H2TPP and ZnTPP obtained by vacuum condensation under quasi-equilibrium conditions is analyzed by sc. The use of analytical methods for processing images of the organic films surface obtained by standard methods, allows to identify not only qualitative, but also quantitative characteristics of the polycrystalline films structure: the average grain size, grain size distribution, the presence of texture and characteristic of crystallites orientations. It is shown that free based H2TPP tetraphenylporphyrin films have a more pronounced texture and a larger crystallite size than ZnTPP, which is due to the peculiarities of self-organization of molecules, if condensation occurs under the same conditions. The applicability of this method of image analysis for obtaining information about the structure and morphology of the surface of thin organic films during vacuum condensation is shown.

The dielectric properties of polycrystalline fullerite films with a thickness of ~300 nm included in p-Si/C60/InGa structures under dc electric fields with a strength up to 3.3 × 107 V/m have been investigated in the frequency range of 30–106 Hz. It is established that, at negative polarity of an InGa electrode (when electron injection from the metal to fullerite is facilitated), an anomalous increase in the sample capacitance is observed at frequencies below 1000 Hz (the capacitance at a low frequency is higher than that at a high frequency by a factor of more than 103). An explanation for this effect is proposed.

In the frequency range from 30 Hz to 1 MHz, the dielectric properties of polycrystalline fullerite films with a thickness of about 300 nm, which are part of p-type Si / C60 / InGa structures, were studied under the influence of constant electric fields with a strength of up to 33 MV / m. It was found that at negative polarity of the InGa electrode, when the injection of electrons from the metal into the fullerite is facilitated, at frequencies less than 1000 Hz, an anomalous increase in the electrical capacity of the sample is observed, while the capacitance at a low frequency exceeds the capacitance at a high frequency by more than 1000 times. An explanation for this effect is proposed.

Electrical characteristics and frequency dependences of dielectric properties ZnTPP thin films in strong fields up to 106 V/cm−1 were measured in present work. The results showed that the conductivity of the films is characterized by a space-charge-limited current model. Conductivity parameters such as traps concentration, energy level and effective carrier mobility were estimated. An increase in conductivity in strong electric fields was observed. A decrease in the dielectric loss tangent with increasing frequency corresponds to the contribution of through-conductivity losses, which increase with increasing applied electric field. Dielectric permittivity increases with an increase in the electric field because of a trap charge accumulation.

Features of the surface topography of a tetraphenylporphyrin film on a graphite single crystal (HOPG) substrate and the local current-voltage characteristics were studied using a scanning tunneling microscope under ambient conditions. STM images of surface were acquired on a scale from a few nanometers to 4 micrometers. Local tunnelling current-voltage characteristics in different ranges of bias voltage and in different directions of voltage scanning can have hysteresis due to the hopping electron conductivity in porphyrin.

Photoluminescence of 5,10,15,20-tetraphenylporphyrin (H2TPP) on nanoporous silicon substrates has been studied. Used nanoporous silicon has a visible PL in the region of H2TPP absorption. Reradiation of porous silicon photoluminescence to the tetraphenylporphyrin long-wavelength peak of the photoluminescence spectrum is observed. The substrate microrelief plays a major role in the formation of tetraphenylporphyrin crystalline structures. The microrelief size of porous silicon was controlled by changing the technological parameters of electrochemical etching.

The purpose of the paper is to assess the experience of Russian students in the online project class. The authors studied the impact of the international project “X-Culture” on the level of development of socio-cultural competencies of students and their knowledge of the English language. An additional aspect of the analysis was the question of the connection of students’ perception of the goal of participation in the international project “X-Culture” with their self-motivation and self-assessment of the success of the results achieved. The study used both quantitative and qualitative methods—student testing, database analysis provided by the project “X-culture”, and focus group records. The result of the participation has been inconsistent. As expected, such sociocultural competence as the level of proficiency in English increased among the majority of students, as confirmed by the values of the student’s criterion for the results of language testing, conducted before and after the project. At the same time, average indicators of sociocultural competences such as “interpersonal skills”, “creativity”, “leadership”, and “friendliness” have deteriorated during the project that is confirmed by the trends lines of time series. The focus group revealed differences in terms of participation in the X-Culture project, their connection with self-motivation, and student satisfaction with the results achieved. Students who have achieved high levels of sociocultural competences have set themselves the goals of participation in the project related to the improvement of professional competencies and intercultural communications. At the same time, students were most satisfied with their activities in the project and the results achieved, aimed at obtaining new professional knowledge and skills, and students whose goal was simply to obtain an international certificate of the project participant.

The optimal geometry of molecules of tetraphenylporphyrin (H2TPP), its zinc complex (ZnTPP) and their dimers and trimers, as well as the HOMO-LUMO energy gap and the binding energies of the complexes, and some other parameters were calculated by quantum chemical method. The calculations of the electronic structure of (MeTPP)(n) complexes were carried out in the framework of the density functional theory with the B3LYP hybrid functional using MOLCAO SCF with atomic sets of basic Gaussian functions 6-3 IIG (2df 2pd) with polarizing d andffitnctions. The difference in energy gain during the formation of dimers and trimers gave an explanation of the self-organization features of different types of porphyrins. The connection between configurations of the basic states of trimers and self-organization properties of selected materials is presented. An explanation of the relationship between the type of porphyrin and its self-organization properties is given. The ground states of the ZnTPP and H2TPP trimers have different geometry configuration - "Zig-zag" for ZnTPP and "Stairs" for H2TPP Due to this fact these materials have different ability to form linear self-organized structures. The energy gain during the formation of the ZnTPP trimer with the optimal configuration is 13.23 kcal/mol, and for H2TPP is 7.79 kcal/mol. It was concluded that ZnTPP is not prone to selfiorganization into linear structures under normal crystallization conditions. Whereas the ground state of (ZnTPP)(3) has a "Zig-zag" geometry, it tends to form planar structures. The large difference between ground and minor states makes it difficult to control self-organization and the growth of nanostructures. The ground state in the geometry of the "Stairs" and the small energy difference between other (H2TPP)(3) configurations, on the contrary, allows growing various modifications of structures, including nanowires, with simple technological changes.

AbstractLong-term exposure of a polycrystalline fullerene C_60 film in a constant electric field of 1–4 MV/cm produces an electroforming effect manifested by increase in conductivity of the film within several orders of magnitude. After this electroforming, the current–voltage ( I – U ) characteristic shows a high degree of current stability and reproducibility of results. In fields of 10^5–10^6 V/cm, the I – U characteristics of electroformed films are determined by the space-charge limited current. The concentration ( N _ t ≈ 4 × 10^21 m^–3) of carrier traps and their energy ( E _ t ≈ 0.176 eV) have been estimated.

AbstractThe goal of this work is to study the processes of self-organization in tetraphenylporphyrin (H_2TPP) films made by condensation under various conditions. Experimental studies of the spectral characteristics of H_2TPP thin films obtained by the liquid method from a H_2TPP toluene solution and by vacuum deposition on different substrates are carried out. It is shown that the structure of the H_2TPP samples changes depending on the technique of synthesis on different substrates, which shows itself in changes (“red” shift) in the photoluminescence and absorption spectra. The changes are caused by a different degree of crystallinity depending on the homogeneity of the surface of the substrates and their temperature.

The goal of this work is to study the processes of self-organization in tetraphenylporphyrin (H2TPP) films made by condensation under various conditions. Experimental studies of the spectral characteristics of H2TPP thin films obtained by the liquid method from a H2TPP toluene solution and by vacuum deposition on different substrates are carried out. It is shown that the structure of the H2TPP samples changes depending on the technique of synthesis on different substrates, which shows itself in changes (“red” shift) in the photoluminescence and absorption spectra. The changes are caused by a different degree of crystallinity depending on the homogeneity of the surface of the substrates and their temperature.

Long-term exposure of a polycrystalline fullerene C60 film in a constant electric field of 1–4 MV/cm produces an electroforming effect manifested by increase in conductivity of the film within several orders of magnitude. After this electroforming, the current–voltage (I–U) characteristic shows a high degree of current stability and reproducibility of results. In fields of 105–106 V/cm, the I–U characteristics of electroformed films are determined by the space-charge limited current. The concentration (Nt ≈ 4 × 1021 m–3) of carrier traps and their energy (Et ≈ 0.176 eV) have been estimated.

The formation of an MEH-PPV/H2TPP nanocomposite, the energy transfer processes leading to the quenching of the photoluminescence of the polymer, and the effects of gamma radiation from a Cs-137 source on the photoluminescence of an MEH-PPV/H2TPP nanocomposite are examined. The dose dependence of the photoluminescence intensity within the range of 0.5-12 kGy in H2O and the processes of photoluminescence recovery after irradiation were studied. The high stability of the radiating properties of the nanocomposite in comparison with the pure polymer is shown. (c) 2019 Optical Society of America.

It has been found that the conductivity of a polycrystalline fullerene C60 thin film increases by several orders of magnitude after lengthy exposure to an electric field of ∼ 106 V/cm. This effect is called electroforming. After electroforming, the current-voltage characteristic shows high current stability and reproducibility of results. An increase in capacitance and a decrease in resistance by 4 orders is observed in a narrow voltage range of 0.1-1 V, which is the effect of reversible resistive switching. In fields with a strength of 105-106 V/cm, the I-V characteristic of molded films is determined by the current with a limited space charge. Trap concentrations are defined as Nt-1 ≈ 2.3· 1021 m−3 and Nt-2 ≈ 5.8·1020 m−3 and their depth Et ≈ 0.17 eV for polycrystalline C60 films with thicknesses of 250 and 500 nm, respectively.

The electrical conductivity of 300 nm thick polycrystalline С60 films on an n-type Si substrate was measured in the range of the electric field strength of 3•104-3•107 V/m at 288-333 K. It has been established that the SCLC regime is implemented in fields above 3•106 V/m. The total concentration of trap states has been estimated at 3•1021 m-3 at a trap depth of 0.35 eV.