K. M. Degtyarenko

Experimental and theoretical study of photo- and electroluminescence of divinyldiphenyl and divinylphenanthrene derivatives

Electronic absorption and luminescence spectra of four new compounds of divinyldiphenyl and divinylphenanthrene derivatives are investigated experimentally in tetrahydrofuran solutions and thin films obtained by thermal vacuum deposition and by spin coating of these substances embedded into polyvinylcarbazole matrix. Molecular geometry optimizations and electronic spectra have been calculated in the framework of XMC-QDPT2/6-31G (d, p) and TDDFT/B3LYP/6-31G (d, p) levels of theory. We have fabricated and studied OLED devices with the structure ITO/PEDOT:PSS/NPD/L/Ca/Al and ITO/PEDOT:PSS/PVK+L/Ca, where L is the luminophore. It is demonstrated that the photo-and electroluminescence spectra of divinyldiphenyl are not identical and undergo strong changes depending on the method of sample preparation.

Organic Nanostructures by Molecular Layer Epitaxy: A Tutorial

This chapter presents a short introduction to molecular layer epitaxy (MLE). MLE is a novel vapor-phase self-assembly approach to create molecular nanoelectronic materials, structures, and devices. The main principles of MLE technology and related topics of surface chemistry are introduced to demonstrate the possibilities of vapor-phase self-assembly, which can be used to achieve desired organic structures and chemical functionalities. We describe equipment, which can produce MLE structures, and monitoring methods used to describe growth of organic MLE structures. We demonstrate several devices, which were produced using MLE technology. These include field-effect transistors (MLE-FETs), organic light-emitting diode (MLE-OLED), MLE solar cells, and MLE laser media. The performance of MLE is compared with other technologies, which are currently used in molecular nanoelectronics, to demonstrate similarities and distinguish features of MLE.

On the conductivity in a two-dimensional molecular π-stack with application to charge transport in DNA solid-state devices

Charge transport in a naphthalene π-stack system can exhibit switching because of variation in its redox state. We study this phenomenon in a molecular π-stack with the aim of obtaining insight into the charge transport in DNA solid-state devices. The model molecular π-stack is based on the structure of naphthalene tetracarboxylic diimide (NTCDI), which is assembled by molecular layer epitaxy (MLE). MLE enables controllable growth of two-dimensional organic frameworks featuring ordered π-stacked arrays of aromatic molecules. These molecular stacks are grown in the in-plane direction with respect to the surface and are bonded covalently to the inorganic semiconducting substrate. In this system, the reduced NTCDI acceptors form redox polarons in which the charge is shared over several molecules within the π-stack. We study the experimental conditions that are required to sustain efficient transport in this redox-capable NTCDI molecular π-stack. The transport in this redox-active system follows the behavior of the polarons. Polaron transport occurs below the HOMO–LUMO gap in a molecular system, for which either ln I ∼ −E−2/3 or I ∼ E (linear regime). We also study the case of redox blockade for the NTCDI molecular π-stack. We demonstrate that the same model (i.e., ln I ∼ −E−2/3) is applicable for transport through DNA molecules positioned between nano-electrodes. Studying the transport in a molecular π-stack enables elucidation of the phenomenon of conductivity switching, which may be responsible for the discrepancies among different transport experiments with DNA solid-state devices. We propose a generalized-effective-medium approach to describe the redox polaron transport in a molecular stack, an approach that is based on a fully compensated semiconductor model.Charge transport in a naphthalene π-stack system can exhibit switching because of variation in its redox state. We study this phenomenon in a molecular π-stack with the aim of obtaining insight into the charge transport in DNA solid-state devices. The model molecular π-stack is based on the structure of naphthalene tetracarboxylic diimide (NTCDI), which is assembled by molecular layer epitaxy (MLE). MLE enables controllable growth of two-dimensional organic frameworks featuring ordered π-stacked arrays of aromatic molecules. These molecular stacks are grown in the in-plane direction with respect to the surface and are bonded covalently to the inorganic semiconducting substrate. In this system, the reduced NTCDI acceptors form redox polarons in which the charge is shared over several molecules within the π-stack. We study the experimental conditions that are required to sustain efficient transport in this redox-capable NTCDI molecular π-stack. The transport in this redox-active system follows the behavior ...

Photo- and electroluminescence of new organic semiconductors

The results of investigation of the luminescence under photo- and electroexcitation for four new compounds are presented. The spectral properties and photoluminescence are studied in ethanol, chloroform solutions and in films formed by thermovacuum deposition (TVD). The phosphorescence of compounds is investigated in ethanol at 77K temperature. The phosphorescence times of molecules are given. The electroluminescence is obtained in multilayered structure ITO/PEDOT/NPD/L /Ca/Al. It is shown, that spectral region of the photoluminescence of TVD films and electroluminescence coincide. Relations of electroluminescence efficiency with molecule structure, photoluminescence quantum yield and possibility of thermally activated delayed fluorescence are discussed.

Photo- and electroluminescence of beryllium and zinc complexes with triazole containing various peripheral substituents

Spectral properties and luminescence under the photo- and electroexcitation of three new zinc and beryllium metal complexes with substituted triazole ligands are investigated. Spectral properties are reported for solutions of chloroform and for films obtained by thermovacuum deposition.

Spectral and electroluminescent properties of coordination compounds of terbium (III) with ibuprofen (in solid form, chloroform solutions, and polyvinylcarbazole films)

Spectral properties of terbium (III) complexes with composition of TbL3DL, where L is an anion of d,l-2-(4-isobutylphenyl)propanoic acid (ibuprofen) and DL is 2,2′-dipyridyl (Dipy), 1,10-phenanthroline (Phen), or triphenylphosphine oxide (TPPO), have been studied in a solid form, chloroform solutions, and polyvinylcarbazole (PVC) films. It has been demonstrated that, in PVC films, occupation of the emitting level of terbium (III) involves the participation of polymer. The emission decay lifetimes of terbium in the chloroform solutions and PVC films have been measured. The possibility of the appearance of electroluminescence of complexes in PVC films has been studied.

Spontaneous and stimulated emissions of copolyfluorenes during photo- and electro-excitation

This review concerns the specific features of photo- and electroexcited processes of excitation energy deactivation in one of the most widely studied classes of organic semiconducting polymers, copolyfluorenes. Spectral-luminescent, electroluminescent, and light-generating properties of a number of copolyfluorenes are discussed, and ways to create organic electronics devices on their basis are revealed.

Active media on the basis of hybrid nanocomposites for tunable lasers

The laser properties and photostability of R6G was investigated in polymer solid-state matrix consisted from copolymers methylmethacrylate (MMA) with 2-hydroxyethylmethacrylate (HEMA) in the 1:1 ratio and in hybrid polymer consisted from the same monomers MMA+HEMA and tetraethoxysilane (TEOS) The 2-nd harmonic of a Nd-YAG laser was used for pumping of active media. It was shown that laser efficiency of R6G in both type of matrix is comparable whereas the laser lifetime of R6G in hybrid material is noticeably longer then in P(MMA+HEMA).

Radiative properties of organic molecules in strong photon fields

We have experimentally investigated the dependence of the luminescence intensity of ethanol solutions of 2-(4-pyridyl)-5-phenyloxazole on the intensity of the exciting radiation from an XeCl laser (λex = 308 nm, τp = 10 nsec, Eex=1022–1026 photons/cm2·sec). We discuss the measurement technique and possible reasons for the change in radiative properties of the investigated solutions under the given conditions.