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Silicon- and carbon-bridged phenylnitroxides were synthesized. They exhibited similar ESR profiles independent of the nature of the sp³ bridge and the substitution mode of the phenylene units. The spectra revealed a quintet signal at room temperature, which became a broad triplet by lowering the temperature. Accumulated ESR measurements at 77 K led to the successful observation of a signal at Δms = 2, indicating that the triplet state was involved in this system.

Dithienosiloles (DTSs) bearing conjugated aryl substituents on the thiophene rings (1 and 2) were prepared and their optical, electrochemical, and electron-transporting properties were investigated in comparison with those of simple DTSs having no conjugated substituents on the thiophene rings (4−6). UV absorption bands of 1 and 2 are red shifted from those of 4−6 by 40−80 nm, reflecting the expanded π-conjugation, whereas the first oxidation peaks in the cyclic voltammograms of 1 and 2 appear at potentials a little lower or almost the same energies relative to those of 4−6, depending on the nature of the substituents. The electron-transporting properties of 1 and 2 were evaluated by the performance of electroluminescent (EL) devices having vapor-deposited DTS, Alq, and TPD layers, as the electron-transport, emitter, and hole-transport, respectively. The results indicated that introduction of aryl substituents to DTSs led to inferior performance of the devices in most cases, while the device with 1c bearing trimethylsilylpyridyl substituents exhibited high efficiency of current−luminance energy conversion and emitted a green light with a maximum luminance of 16 000 cd/m². A trap-controlled electron transporting model is proposed to explain their performance.

Polymers with alternating mono-, di-, or trisilanylene units and 2,5-oligothienylene groups, [(SiR2)x(C4H2S)m]n (R = Me, Et, x = 1−3, m = 2−5), were synthesized and their optical, conducting, and hole-transporting properties were investigated. The UV absorption and emission maxima of the polymers shift to lower energies as the number of thienylene groups (m) between the silanylene units increases, while they are little affected by the silicon chain length (x). When the polymer films were exposed to FeCl3 vapor, semiconducting films with the conductivities of 1.3 × 10^-4−2.3 × 10^-1 S/cm were obtained. The conductivities tend to increase with m but decrease with increasing x. The double-layer-type EL devices were fabricated using some of the polymers (x = 1, m = 3−5; x = 2, m = 4) as the hole-transporting layer and tris(8-quinolinolato)aluminum(III) (Alq) as the electron-transporting-emitter layer. Reducing the number of m and x resulted in a high-voltage shift in the turn-on voltage and a decrease in the maximum current density of the device. The highest luminance of 2000 cd/m² was obtained from a device based on the disilanylene−tetrathienylene alternating polymer (x = 2, m = 4).

UV irradiation of poly[(tetraethyldisilanylene)(3,4-diethynylenesilole)] in the presence of an excess of Fe(CO)5 led to the formation of Fe(CO)3-coordinated silole units in the polymer backbone. The ratio of the Fe(CO)3-coordinated and noncoordinated units in the resulting polymer was determined to be 2:1 by ¹H NMR spectrometry. Similar treatment of poly[(tetramethyldisilanylene)(3,4-diethynylenesilole)] also afforded the corresponding Fe(CO)3-coordinated polymer. The polymers with Fe(CO)3-coordinated silole units exhibit slightly red-shifted UV absorption bands, relative to the parent noncoordinated polymers. When doped with FeCl3 vapor, the Fe(CO)3-coordinated polymers became semiconducting with conductivities on the order of 10^-5 S/cm, much higher than the conductivities of the parent polymers doped with FeCl3, which were determined to be less than 10^-8 S/cm. Crystal structures of two model compounds having Fe(CO)3-coordinated or noncoordinated 3,4-diethynylenesilole units were determined by X-ray crystallography, which suggest enhanced π-conjugation in the Fe(CO)3-coordinated 3,4-diethynylenesilole ring as compared with the noncoordinated one.

A series of bithiophene derivatives bearing an intramolecular monosilanylene or disilanylene bridge between the β,β‘-positions were synthesized, and their properties were investigated. UV spectral and cyclic voltammetric analyses of the silicon-bridged bithiophenes indicated that they have lower lying LUMOs, relative to those for bithiophene and methylene bridged bithiophenes, probably due to σ*−π* interaction between the silicon atom(s) and bithiophene π-orbitals, in good agreement with the results of theoretical calculations using simplified model compounds based on RHF/6-31G. The silicon-bridged bithiophenes exhibit high electron-transporting properties, and triple-layer-type electroluminescent (EL) devices, using the silicon-bridged bithiophenes, tris(8-quinolinolato)aluminum(III) complex (Alq), and N,N‘-diphenyl-N,N‘-di-m-tolylbiphenyl-4,4‘-diamine (TPD) as the electron-transporting, emitting, and hole-transporting layers, respectively, emitted strong EL.

Photoinduced reactions of trans-HC&tbd1;CH^- in a glassy 2-MTHF matrix were studied by ESR and electron absorption (EA) spectroscopy. ESR and EA spectra were interpreted with the aid of the results of molecular orbital (MO) calculations. The trans-HC&tbd1;CH^- was generated and stabilized in the 2-MTHF matrix at 77 K by ionizing irradiation. The ESR parameters observed for the radical anion are A1 = 5.3, A2 = 4.6, A3 = 4.5 mT for two equivalent ¹H atoms, A⊥ = 1.5, A∥ = 4.2 mT for two equivalent ¹³C atoms, and g1 = 2.0009, g2 = 2.0024, g3 = 2.0029 for the g tensor. By illuminating with light of λ ≥ 430 nm, the trans-HC&tbd1;CH^- was found to be irreversibly isomerized into the vinylidene radical anion, H2C&dbd;C^-, in the matrix. The experimental ESR parameters of H2C&dbd;C^- [A1 = 5.4, A2 = 6.0, A3 = 5.7 mT for two equivalent protons, g1 = 2.0026, g2 = 2.0008, g3 = 2.0026] were fully consistent with the results obtained by semiempirical MO methods, (1) INDO and Analytical Dipolar Calculation method (ANADIP) for isotropic and anisotropic ¹H hyperfine (hf) couplings, respectively, and (2) AM1 for the g tensor, for a geometrical structure optimized by ab initio method (Gaussian90/uhf/6-31++G**). The structure of the anions was in agreement with the results obtained from the EA spectroscopic study. The photoinduced isomerization was initiated by the light absorption at λ ≥ 430 nm of trans-HC&tbd1;CH^-. The EA band at λmax = 374 nm observed for H2C&dbd;C^- was attributed to the electron transition from the ²B2 ground state and to the ²A1 excited state.

High-resolution EPR spectra of CH3, ¹³CH3, and even CH2D radicals with their natural abundances have been observed in Ar matrix in the temperature range 4.2−40 K. This was achieved by X-ray radiolysis of Ar matrix containing 0.2 mol % CH4. The high-resolution EPR spectra of CD3 and CHD2 radicals were also obtained under similar conditions using CD4 and CH2D2 instead of CH4, respectively. At the lower temperatures, the EPR line shapes of these radicals are dominated by hyperfine (hf) patterns with anomalous intensity, attributed to quantum effects. The application of the Pauli principle in combination with D3 point-group symmetry results in interesting exclusion of EPR transitions for both the α-proton- and the α-deuteron-rotor spectra. In contrast to the β-proton methyls >^•C−CH3, the hf coupling is anisotropic and no rotation-hindering barrier is present here. The “E” lines of the corresponding isotropic β-proton methyl rotor [Sørnes, A. R.; Benetis, N. P. Chem. Phys. 1998, 226, 151]¹ are absent from their regular positions. The deuteron rotor is giving a peculiar spectrum at the lowest experimental temperature, i.e., an extremely strong central singlet superimposed on a much weaker fast motional spectrum. The quantum effects are attributed to spin-rotation coupling through the anisotropic part of the hf interaction and exchange symmetry of at least two identical fermions or bosons of the studied radicals. The experimental findings are consistent with a three-dimensional, free quantum-rotor motional model.

Abstract: PAL were measured for several low molecular organic compounds, normal and cyclic-hydrocarbons and their perfluorinated ones, from room temperature down to about 40 K, and information about the vacancies in them has been extracted from tau3 andI 3. Normally the size of vacancies were larger in the solids comprising larger molecules, showing thato-Ps can represent the vacancy size. In a special case of perfluorocyclohexane whose solid had to be prepared by sublimation the vacancy size was larger than expected. In all the solid molecules studied twoo-Ps states could be observed and their relative importance could easily change showing a hysteresis-like behavior. At further lower temperatures of around 40 K theo-Ps state with longer lifetime and larger intensity became overwhelming for all molecules. Also tau3 andI 3 were not very sensitive to most of the phase transitions, including the melting points.

Cyclic voltammetry of KI at high concentrations was studied on Pt and polyaniline-modified Pt electrodes in 0.1 m HClO4 solution. The oxidation of iodide to iodine proceeded at a polyaniline-filmed Pt electrode with a mechanism similar to that at a bare Pt electrode. New peaks appeared in the cyclic voltammograms on the polyaniline-filmed Pt electrodes, depending on the experimental conditions, due to interactions of iodine species with the polyaniline chains. XPS analysis of polyaniline samples doped with iodine during, or after, the synthesis of polyaniline provided further evidence of the existence of polyaniline-iodine charge transfer complexes.