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

Anomalous Thermal Stability of Metastable C_20 Fullerene

The results of computer simulation of the dynamics of fullerene C_20 at different temperatures are presented. It is shown that, although it is metastable, this isomer is very stable with respect to the transition to a lower energy configuration and retains its chemical structure under heating to very high temperatures, T ~ 3000 K. Its decay activation energy is found to be E_a ~ 7 eV. Possible decay channels are studied, and the height of the minimum potential barrier to decay is determined to be U = 5.0 eV. The results obtained make it possible to understand the reasons for the anomalous stability of fullerene C_20 under normal conditions.Comment: Slightly corrected version of the paper submitted to Phys. Solid Stat

Formation of a "Cluster Molecule" (C20)2 and its thermal stability

The possible formation of a "cluster molecule" (C20)2 from two single C20 fullerenes is studied by the tight-binding method. Several (C20)2 isomers in which C20 fullerenes are bound by strong covalent forces and retain their identity are found; actually, these C20 fullerenes play the role of "atoms" in the "cluster molecule". The so-called open-[2+2] isomer has a minimum energy. Its formation path and thermal stability at T = 2000 - 4000 K are analyzed in detail. This isomer loses its molecular structure due to either the decay of one of C20 fullerenes or the coalescence of two C20 fullerenes into a C40 cluster. The energy barriers for the metastable open-[2+2] configuration are calculated to be U = 2 - 5 eV.Comment: 21 pages, 8 figure

Metastable quasi-one-dimensional ensembles of nitrogen clusters N_8

By means of ab initio and tight-binding calculations it is shown that metastable nitrogen clusters N_8 (boats) can form quasi-one-dimensional ensembles in which the nearest clusters N_8 are bound to each other by covalent bonds. Those ensembles are characterized by rather high energy barriers (~ 0.3 eV) that prevent the fission of the ensembles into isolated N_8 clusters and/or N_2 molecules.Comment: 3 pages, 4 ps figure

Decay and fusion as two different mechanisms of stability loss for the (C_20)_2 cluster dimer

The thermal stability of the (C_20)_2 cluster dimer consisting of two C_20 fullerenes is examined using a tight-binding approach. Molecular dynamics simulations of the (C_20)_2 dimer at temperatures T = 2000 - 3500 K show that the finite lifetime \tau of this metastable system is determined by two fundamentally different processes, the decay of one of the C_20 fullerenes and the fusion of two C_20 fullerenes into the C_40 cluster. The activation energies for these processes Ea = 3.4 and 2.7 eV, respectively, as well as their frequency factors, have been determined by analyzing the dependence of \tau on T.Comment: Slightly modified version of the paper to appear in JETP Let

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