Two-photon spectroscopy of the biphenyl chromophore. The electronic excited states of biphenyl and fluorene below 50000 cm-1

The two-photon excitation spectra of biphenyl and fluorene in dil. soln. were measured up to 50,000 cm-1. Both spectra exhibit a medium intense band system in the range 32,000-42,000 cm-1, and a strong band above 45,000 cm-1. The lowest frequency feature is assigned to a B3 symmetry transition in biphenyl and the corresponding B2 transition in fluorene. The polarization of the higher bands leads to the assignment of 2 A states at 38,000 and 47,000 cm-1. The origin of the electronically excited states of the biphenyl chromophore is discussed by simple composite mol. considerations as well as CNDO CI calcns. The latter give a semiquant. picture of transition energies and transition probabilities for 1- and 2-photon allowed excitations. A compilation of 1-photon spectra and calcns. from the literature is included in the anal. to provide a consistent picture of the electronically excited states of the biphenyl chromophore up to 50,000 cm-1

1,6-Interactions between dimethylamino and aldehyde groups in two biphenyl derivatives

The title compounds, 2-(dimethylamino)biphenyl-2'-carboxaldehyde, C15H15NO, and 2-(dimethylamino)biphenyl-2',6'-dicarboxaldehyde, C16H15NO2, show similar 1,6-interactions [N...C=O 2.929 (3) to 3.029 (3) Å] between the dimethylamino and aldehyde groups located in the ortho positions of the two rings, which lie at 58.1 (1)-62.4 (1)° to each other

Influencing the conductance in biphenyl-like molecular junctions with THz radiation

We investigate the torsional vibrations in biphenyl-like molecular junctions and transport properties in the presence of an external THz field. Ab-initio calculations including external electric fields show that the torsional angle {\phi} of a thiolated biphenyl junction exhibits virtually no response. However, if functional groups are added to the molecule, creating a dipole moment in each of the rings, an external field becomes more effective for changing {\phi}. A model based on the cos2{\phi} dependence of the current is proposed for the biphenyl-like molecular junctions in presence of an external THz field including 2,2'-bipyridine, 3,3'-bipyridine and 2,2',4,4'- tetramethyl-3,3'-bipyridine. The current through these molecules is shown to change if the THz frequency gets in resonance to the torsional vibration mode.Comment: 9 pages, 10 figures, submitted to PSS

A Suzuki Coupling Based Route to 2,2'-Bis(2-indenyl)biphenyl Derivatives

Because of the promising performance in olefin polymerization of 2,2'-bis(2-indenyldiyl)biphenyl zirconium dichloride, we developed a new and broadly applicable route to 2,2'-bis(2-indenyl)biphenyl derivatives. Reaction of the known 2,2'-diiodobiphenyl with the new 2-indenyl boronic acid did not result in the desired 2,2'-bis(2-indenyl)biphenyl (10); instead an isomer thereof, (spiro-1,1-(2,2'-biphenyl)-2-(2-indenyl)indane), was obtained. It was found that compound 10 could be made via a palladium-catalyzed reaction of 2,2-biphenyldiboronic acid with 2-bromoindene under standard Suzuki reaction conditions. However, the yield of this reaction was low at low palladium catalyst loadings, due to a competitive hydrolysis reaction of 2,2-biphenyldiboronic acid. HTE techniques were used to find an economically viable protocol. Thus, use of the commercially available 1.0 molar solution of (n-Bu)4NOH in methanol with cosolvent toluene led to precipitation of the pure product in a fast and clean reaction, using only 0.7 mol % (0.35 mol % per C-C) of the expensive palladium catalyst.

Hierarchically structured biphenylene-bridged periodic mesoporous organosilica

Novel composites of highly ordered and stable biphenyl-bridged periodic mesoporous organosilica (PMO) materials confined within the pores of anodic alumina membranes (AAM) were successfully synthesized by evaporation-induced self-assembly (EISA). 4,40-Bis(triethoxysilyl)biphenyl (BTEBP) was used as a precursor in combination with the ionic surfactant cetyltrimethylammonium bromide (CTAB) or triblock-copolymer F127 as structure-directing agents. The resulting mesophases were characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). With ionic CTAB as a structure directing agent, samples with a mixture of the 2D-hexagonal columnar and a lamellar mesophase were obtained within the AAM channels. When using the nonionic surfactant F127, mesophases with a 2D-hexagonal circular structure were formed in the AAM channels. Additionally, a cubic Im3m phase could also be obtained with the same nonionic surfactant after the addition of lithium chloride to the precursor solution. The stability of both the circular and cubic biphenylene-bridged PMO against calcination temperatures of up to 250 °C was confirmed by NMR spectroscopy. Nitrogen sorption in the porous composite membrane shows typical type IV isotherms and narrow pore size distributions. All the biphenyl PMO/AAM composites show fluorescence due to the existence of biphenyl chromophores in the stable organosilica framework

Ideal gas thermodynamic properties for the phenyl, phenoxy, and o-biphenyl radicals

Ideal gas thermodynamic properties of the phenyl and o-biphenyl radicals, their deuterated analogs and the phenoxy radical were calculated to 5000 K using estimated vibrational frequencies and structures. The ideal gas thermodynamic properties of benzene, biphenyl, their deuterated analogs and phenyl were also calculated

Orbital Interaction Mechanisms of Conductance Enhancement and Rectification by Dithiocarboxylate Anchoring Group

We study computationally the electron transport properties of dithiocarboxylate terminated molecular junctions. Transport properties are computed self-consistently within density functional theory and nonequilibrium Green's functions formalism. A microscopic origin of the experimentally observed current amplification by dithiocarboxylate anchoring groups is established. For the 4,4'-biphenyl bis(dithiocarboxylate) junction, we find that the interaction of the lowest unoccupied molecular orbital (LUMO) of the dithiocarboxylate anchoring group with LUMO and highest occupied molecular orbital (HOMO) of the biphenyl part results in bonding and antibonding resonances in the transmission spectrum in the vicinity of the electrode Fermi energy. A new microscopic mechanism of rectification is predicted based on the electronic structure of asymmetrical anchoring groups. We show that the peaks in the transmission spectra of 4'-thiolato-biphenyl-4-dithiocarboxylate junction respond differently to the applied voltage. Depending upon the origin of a transmission resonance in the orbital interaction picture, its energy can be shifted along with the chemical potential of the electrode to which the molecule is more strongly or more weakly coupled

Synthesis And Characterization Of Polyynes End-Capped By Biphenyl Groups ({\Alpha},{\Omega}-Biphenylpolyynes)

Stable polyyne chains terminated with biphenyl end groups (a,u-biphenylpolyynes) were synthesized in a single step through a simple procedure by using the Cadiot-Chodkiewicz reaction conditions. The a,ubiphenylpolyynes were separated through HPLC analysis and identified by means of their electronic absorption spectra. The a,u-biphenylpolyynes were studied by FT-IR and Raman spectroscopy and the spectral interpretation was supported with DFT calculations. A peculiarly low reactivity of a,u-biphenylpolyynes with ozone was observed.Comment: The research leading to these results has received funding from the European Research Council Consolidator Grant EspLORE (ERC-2016-CoG Grant No.724610

Molecular Orbital Models of Benzene, Biphenyl and the Oligophenylenes

A two state (2-MO) model for the low-lying long axis-polarised excitations of poly(p-phenylene) oligomers and polymers is developed. First we derive such a model from the underlying Pariser-Parr-Pople (P-P-P) model of pi-conjugated systems. The two states retained per unit cell are the Wannier functions associated with the valence and conduction bands. By a comparison of the predictions of this model to a four state model (which includes the non-bonding states) and a full P-P-P model calculation on benzene and biphenyl, it is shown quantitatively how the 2-MO model fails to predict the correct excitation energies. The 2-MO model is then solved for oligophenylenes of up to 15 repeat units using the density matrix renormalisation group (DMRG) method. It is shown that the predicted lowest lying, dipole allowed excitation is ca. 1 eV higher than the experimental result. The failure of the 2-MO model is a consequence of the fact that the original HOMO and LUMO single particle basis does not provide an adequate representation for the many body processes of the electronic system.Comment: LaTeX, 12 pages, 3 eps figures included using epsf. To appear in Chemical Physics, 199