Optical band gap modification of single-walled carbon nanotubes by encapsulated fullerenes

We report optical band gap modifications of single-walled carbon nanotubes upon C60 insertions by using photoluminescence and the corresponding excitation spectroscopy. The shifts in optical transition energies strongly depend on the tube diameter (dt) and the "2n + m" family type, which can be explained by the local strain and the hybridization between the nanotube states and the C60 molecular orbitals. The present results provide possible design rules for nanotube-based heterostructures having a specific type of electronic functionality.     

Electron irradiation induced microstructural modifications in BaCl2 doped PVA: A positron annihilation study

Thin films of pure and 10 wt% BaCl₂ doped poly(vinyl alcohol) (PVA) were prepared by solution casting method. These films were subjected to electron irradiation for different doses ranging from 0 to 400 kGy in air at room temperature. The effect of electron irradiation on the optical and free volume related microstructures of these polymer films was studied using positron annihilation lifetime spectroscopy, FTIR and UV-vis techniques. The FTIR spectral studies indicate that the electron irradiation induces chemical modifications within the doped PVA, which results in chain scission as well as cross-linking of the polymer. The positron lifetime study on these irradiated polymers shows that the chain scissions and cross-linking within the polymer matrix affect the free volume content and hence the microstructure. The UV-vis optical absorption studies show that the induced microstructural change by electron irradiation also modifies the optical properties. Using UV-vis spectra, the optical energy band gap was estimated and it decreases with increase in electron dose. A correlation between positron results and optical results is obtained and electron irradiation induced microstructure modifications within the doped polymer are understood. The results highlight the usefulness of positron annihilation technique in the study of the microstructure of irradiated polymers.     

Novel enantioselective fluorinating agents, (R)- and (S)-N-fluoro-3-tert-butyl-7-nitro-3,4-dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides

Enantioselective fluorinating agents, (R)- and (S)-,N-fluoro-3-tert-butyl-7-nitro-3,4-dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides (BNBT-F, 2) are readily prepared in 3 steps from racemic 3-tert-butyl-7-nitro-3,4-dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxides (5) via optical resolution and fluorination. These agents make accessible both enantiomers of optically active quaternary alpha-fluoro carbonyl compounds in modest to high enantioselectivities. X-ray crystallographic analysis of chiral 2 reveals a unique structure wherein the nitrogen atom is highly pyramidalized and fluorine occupies an axial position.     

Synthesis and electroluminescent properties of soluble poly(3,6-fluorene) and its copolymer

Soluble poly(3,6-fluorene) and its copolymer were synthesized by nickel-catalyzed coupling. Poly(3,6-fluorene) exhibited the optical band gap of 3.6 eV, the emission maximum at 347 nm, and the HOMO level of -6.05 eV. These results confirm that 3,6-linkage is an effective way to get wide band gap conjugated polymers. Furthermore, its copolymer containing triarylamine moieties emits deep-blue light, which means that the adjustable blue light emission can be obtained from their copolymers via energy transfer.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds-II

At room temperature, three of the six polymorphic compounds described are not present in their highest melting-point form, owing to enantiotropy. These three are triphenyltin chloride (3 modifications), 1-(4,4-dimethyl-2-oxo-3-tetrahydrofuryl)thiourea (4 modifications), and 2-aminoethyl diphenylborinate (3 modifications). In the case of 4-amino-1-(2-phenylethyl)-1,2,4-triazoline-5-thione, in addition to the absolutely stable modificationI, a further six unstable crystal forms have been observed. The three modifications of,-dimethyl-[1,1-biphenyl]-4-methanol are also monotropic in character. 2,9-Dimethyl-1,10-phenanthroline, the three polymorphic forms of which are unstable, is a special case, since it absorbs water from the air and changes into a semi-hydrate.     

Hexagonal supramolecular architectures from ferrocenium cations incorporating [Ni(mnt)2]- columns: structures and properties of [alkylferrocene][Ni(mnt)2]- charge-transfer complexes (mnt=maleonitriledithiolate)

The crystal architecture, magnetic properties, and thermodynamic properties of [n-butylferrocene][Ni(mnt)2] (1), [tert-butylferrocene][Ni(mnt)2] (2), [1,1'-diethylferrocene][Ni(mnt)2] (3), and [1,1'-diisopropylferrocene][Ni(mnt)2] (4) were investigated (mnt=maleonitriledithiolate). These complexes exhibit a unique supramolecular structure in which the ferrocenium cations constitute honeycomb-like assembled structures surrounding columns of the anions. For 1, the cations form a dimer through a very short intermolecular ferrocene-ferrocene distance of 3.28 A, which mediates an antiferromagnetic interaction with a singlet-triplet energy gap of 5 K. First-order phase transitions occur in 1-3 at 364, 361, and 350 K, respectively, accompanied by thermal hysteresis.     

Calculation of the inductive interaction of two dipoles

The electrostatic interaction is calculated for the dipoles in 1,1-dichloroethylene, dichloroaryl compounds, and some alicyclic 1,2-dihalo compounds and -haloketones. The induced dipoles, bond moments, and molecular dipole moments are calculated. Most of the results agree well with experiment. The induction is found to be dependent on the separation and mutual orientation of the dipoles rather than on the number of bonds between them. It is concluded that the field effect is decisive in induction and that transmission via chains of atoms is relatively unimportant.     

Simple non-fullerene electron acceptors with unfused core for organic solar cells

Two simple unfused-cores based electron acceptors with different side units were developed for application in non-fullerene solar cells, in which the side chains have the significant effect on their absorption spectra and photovoltaic performance.     

3,4‐Dithiaphosphole and 3,3′,4,4′‐Tetrathia‐1,1′‐Biphosphole π‐Conjugated Systems: S Makes the Impact

Conjugated systems based on phospholes and 1,1′‐biphospholes bearing 3,4‐ethylenedithia bridges have been prepared using the Fagan–Nugent route. The mechanism of this organometallic route leading to intermediate zirconacyclopentadienes has been investigated by using theoretical calculations. This study revealed that the oxidative coupling leading to zirconacyclopentadienes is favored over oxidative addition within the S? C≡C bond both thermodynamically and kinetically. The impact of the presence of the S atoms on the optical and electrochemical behavior of the phospholes and 1,1′‐biphospholes has been systematically evaluated both experimentally and theoretically. A comparison with their “all‐carbon” analogues is provided. Of particular interest, this comparative study revealed that the introduction of S atoms has an impact on the electronic properties of phosphole‐based conjugated systems. A decrease of the HOMO–LUMO separation and a stabilization of the LUMO level were observed. These general trends are also observed with 1,1′‐biphospholes exhibiting σ–π conjugation. The P atom of the 3,4‐ethylenedithiaphospholes can be selectively oxidized by S₈ or O₂. These P modifications result in a lowering of the HOMO–LUMO separation as well as an increase of the reduction and oxidation potentials. The S atoms of the 3,4‐ethylenedithia bridge of the 2,5‐phosphole have been oxidized using m‐chloroperoxybenzoic acid. The resulting 3,4‐ethylenesulfoxide oxophosphole was characterized by an X‐ray diffraction study. Experimental and theoretical studies show that this novel chemical manipulation results in an increase of the HOMO–LUMO separation and an important decrease of the LUMO level. The electropolymerization of 2‐thienyl‐capped 3,4‐ethylenedithiathioxophosphole and 1,1′‐biphosphole is reported. The impact of the S substituents on the polymer properties is discussed.     

Organophosphorus π-conjugated materials: the rise of a new field

The synthesis and electronic properties of new linear organic π-conjugated systems incorporating phosphole rings are described. Well defined α,α′-(phosphole-thiophene) oligomers possess low HOMO-LUMO gaps and their optical and electrochemical properties can be tuned via chemical modifications of the P-atoms. The physical properties of these compounds make them valuable materials for OLED’s. The coordination ability of phosphole-based dipoles has been exploited for the synthesis of efficient multipolar NLO-phores. Lastly, phospholes have been used for the synthesis of assemblies exhibiting through-bond interaction between two π-systems via P-P σ-skeletons.     

The synthesis and characterization of α- and β-1, 1-diiodo-3,4-benzo-1-telluracyclopentane,C8H8Tel2

Elemental Tellurium reacts with α,α′-dichloro-o-xylene and NaI in 2-methoxyethanol to form 1,1-diiodo-3,4-benzo-1-telluracyclopentane in 83% yield. C₈H₈TeI₂ is molecular in acetone, methylene chloride and methyl ethyl ketone, but ionic in DMF. Two crystalline modifications of the compound have been isolated from 2-methoxyethanol. The yellow-orange or α form is monoclini?, space group P2₁/c; the orange-red or β form is also monoclinic, space group I2/c. Infrared, optical and mass spectral data, along with solution UV, NMR, molecular weight and conductivity data, suggest that the two crystalline modifications are plymorphs, possibly differing in the degree and type of heavy atom interaction. In 2-methoxyethanol the β form undergoes a solution phase transformation to the stable α form. Both forms are thermochromic.     

Theoretical investigations on electronic structures and photophysical properties of N-heteroaryl carbazole derivatives as host materials

The carbazole-endcapped host molecules with tailoring different heteroaryl core and meta-position linkage mode have great potential on phosphorescent organic light-emitting diodes. To provide a profound view on structure?Cproperty relationships, new linear-shaped counterparts have been designed based on the existing molecular composition and the linkage at para-position (p-type molecules). A series of studies about the influence of the linkage mode on optical and electronic properties of these carbazole derivatives have carried out via density functional theory and time-dependent density functional theory calculations. The geometric and the electronic structure of these molecules in the ground states, ions states, and lowest triplet states have been calculated especially focusing on the analysis of highest occupied molecular orbitals, lowest unoccupied molecular orbitals, energy gaps, triplet energies, ionization potentials, electron affinities, reorganization energies, triplet exciton-formation fraction, and absorption spectra. These optoelectronic properties can be effectively tuned by the chemical modifications of different linkage pattern. The good coordination between our calculated results and the available experimental data has been observed. The study reveals that the designed p-type molecules show great promise as new high-performance red host materials with large triplet energy, narrow energy gap, good electron and hole-transport properties, and high triplet exciton-formation fraction.     

ZnS nanoparticles incorporated in polyaniline composite: Preparation and optical characterization

Hybrid polyaniline based composites incorporating zinc sulfide nanoparticles have been synthesized by using chemical oxidation technique. Morphological and optical properties of the nanocomposite were characterized by scanning electron microscopy, Fourier transform infrared and UV–Vis spectroscopy measurement. The results were compared with pure polyaniline. The characteristic FTIR peaks of polyaniline were found to shift to lower wave-number in nanocomposite. The band gap of nanocomposites increases and the refractive index of the nanocomposites decreases with increasing content of ZnS nanoparticles. These results showed the interaction between ZnS nanoparticles and polyaniline.     

A parallel colorimetric method for the rapid discovery and optimization of heterogeneous hydrodesulfurization catalysts

A spectrophotometric based, parallel approach to screen heterogeneous catalysts for hydrodesulfurization has been developed. The method utilizes optical changes resulting from the hydrodesulfurization of 1,1'-binaphthothiophene to 1,1'-binaphthyl to determine catalyst activity. Hydrodesulfurization of 1,1'-binaphthothiophene to 1,1'-binaphthyl results in a loss of conjugation in the binaphthyl ring system. This results in a blue shift of more than 60 nm in the UV-vis spectrum. Since only small amounts of the HDS catalyst and 1,1'-binaphthothiophene are required, a large number of catalysts may be screened simultaneously. The synthesis of the 1,1'-binaphthothiophene and conditions for HDS catalyst screening are described.     

SCF—CI calculations and the assignment of the absorption spectrum of the excimer of 1-methyl naphthalene; relation to 1,1′-binaphthyl

An SCF MO calculation followed by extensive configuration interaction between all singly-excited singlet states has been performed for the excimer of naphthalene in a perfect and in some distorted sandwich structures. With these results an assignment is given for the bonds in the absorption spectrum of the excimer of 1-methyl naphthalene. It is further shown that the similarity between the optical properties of the 1-methyl naphthalene excimer and those of 1,1′-binaphthyl in fluid solution, is also reflected by the calculations.     

Nature of the chemical bond between metal atoms and oxide surfaces: new evidences from spin density studies of K atoms on alkaline earth oxides

We have studied the interaction of K atoms with the surface of polycrystalline alkaline-earth metal oxides (MgO, CaO, SrO) by means of CW- and Pulsed-EPR, UV-Vis-NIR spectroscopies and DFT cluster model calculations. The K adsorption site is proposed to be an anionic reverse corner formed at the intersection of two steps, where K binds by more than 1 eV, resulting in thermally stable species up to about 400 K. The bonding has small covalent and large polarization contributions, and the K atom remains neutral, with one unpaired electron in the valence shell. The interaction results in strong modifications of the K electronic wave function which are directly reflected by the hyperfine coupling constant, (K)a(iso). This is found to be a very efficient "probe" to measure the degree of metal-oxide interaction which directly depends on the substrate basicity. These results provide an original and general model of the early stages of the metal-support interaction in the case of ionic oxides.     

A novel mercapto-bisphosphonate as an efficient anticalcification agent for bioprosthetic tissues

The synthesis of 2-(2-mercaptoethylamino)ethylidene-1,1-bisphosphonic acid (2) is reported (overall yield >90%), via nucleophilic addition of cystamine to vinylidene-bisphosphonic acid (1) followed by reduction of disulfide bonds with Me₃P. Reaction of 1 with cysteamine forms the isomeric 2-(2-aminoethylthio)ethylidene-1,1-bisphosphonate (3) in an almost quantitative yield. Thiol groups of 2 in water at pH 7 react with epoxy rings more than 30 times faster compared to the known 2-mercaptoethylidene-1,1-bisphosphonate. Elimination of the thiol group is observed as a side-reaction in the reduction of disulfides with phosphines. Stabilization of bioprosthetic tissues with triglycidylamine in the presence of 2 results in covalent immobilization of 2 via an epoxy-SH reaction; this inhibits the long-term calcification of bioprosthetic heart valve tissues to almost undetectable levels.     

Linear and nonlinear optical susceptibilities for a novel borate oxide BaBiBO4: Theory and experiment

The linear and nonlinear optical susceptibilities for different tensor components of BaBiBO₄ single crystals have been calculated using the full-potential linear augmented plane wave method. The results of these calculations are verified by our measurements of linear and nonlinear optical properties using Nd-YAG laser at fundamental wavelength 1064 nm. The calculated energy gap is in a good agreement with experimental energy gap data obtained by optical absorption. We present results for the imaginary and real parts of the frequency-dependent dielectric constant. The calculated birefringence of BaBiBO₄ is positive in agreement with the experimental data. Calculations are reported for the frequency-dependent complex part of second-order nonlinear optical susceptibilities . The linear and nonlinear optical susceptibilities are scissors corrected to match the value of the energy gap from the local density approximation calculations with the experimental value. The second harmonic generation efficiency of this compound is about five times larger than KDP (KH₂PO₄). It is crucial that we have obtained a large anisotropy of the second-order susceptibilities for three main second-order tensor components both experimentally and theoretically. The possible origin of the obtained anisotropy is discussed within a framework of the energy band calculations.     

M···π-conjugated complexes: simple materials with dramatic NLO features (M = Li,Na, K,and π = butadiene,cyclobutadiene, hexatriene,benzene)

Theoretical investigation of linear and nonlinear optical (NLO) properties in simple complexes consist of alkali metals and π-conjugated systems have been studied at MP2/6-311++G(2d,2p) computational level. Lithium, sodium, and potassium as alkali metals were chosen for interaction with some non-aromatic, aromatic and anti-aromatic systems. For better comparison of results, the π-systems were chosen with the same carbon number: butadiene as a non-aromatic in comparison with cyclobutadiene as an anti-aromatic and hexatriene as a non-aromatic in comparison with benzene as an aromatic system. Results revealed that gap energy of studied π-systems was decreased under the interacting with alkali metals. Furthermore all designed complexes were shown very good results in average polarizability (α) and first hyperpolarizability (β ₀) parameters. So these very simple dimer complexes could be introduced as promising innovative nonlinear optical materials.     

Intramolecular interaction in aryldihydrothiophene 1,1-dioxides

The peculiarities of the intramolecular interaction in unsaturated five-membered cyclic sulfones as a function of their structures were studied on the basis of an analysis of the electronic absorption spectra of single crystals of isomeric -aryldihydrothiophene 1,1-dioxides at 4.2°K, the IR spectra of the molecules at 298°K, and the results of x-ray diffraction analysis of 3-phenyl-4,5-dihydrothiophene 1,1-dioxide. In addition to the inductive effect, conjugation of the SO₂ group with the -electron system of 3-phenyl-4,5-dihydrothiophene 1,1-dioxide, which is manifested most appreciably in the excited electronic state, was observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1056–1059, August, 1977.