A novel picosecond laser approach is used to investigate the intrinsic fluorescence of several oligonucleotides. All biomolecules are excited at 283 nm with laser pulses of typically 80 ps duration and an energy of 250 µJ; concentrations were on the order of 10 -5 M. Detection of the resulting fluorescence behind a spectrometer with a streak camera permits the simultaneous acquisition of spectral and lifetime information in two-dimensional images. In a systematic study, the fluorescence spectra and the associated temporal decays are analyzed with respect to monomer and potential excimer components. For this, the nucleotides AMP, CMP, GMP, and TMP are studied as well as homo-oligonucleotides of the type d(X) n with variable sequence length of n ) 2-15, enabling a comparison of the emission characteristics of these single-stranded compounds under physiologic conditions in solution at room temperature. Also, the influence of conformational changes on the fluorescence response is investigated using mixtures of complementary oligonucleotides d(X) 15 ×d(Y) 15 with the combinations X ) A, Y ) T and X ) G, Y ) C. These structures, which form double helices, differ in flexibility and stacking geometry from the single-stranded compounds. From experiments with self-complementary variants with alternating base sequences of the type d(XY) 8 with XY ) AT and GC, information on exciplex formation tendencies is obtained for these compounds, which also form double helices in solution. Preliminary results of time-dependent fluorescence anisotropy measurements with this direct picosecond laser approach are discussed.

Seven derivatives of 1,2-dicarbadodecaborane (ortho-carborane, 1,2-C(2)B(10)H(12)) with a 1,3-diethyl- or 1,3-diphenyl-1,3,2-benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low-energy fluorescence emissions with large Stokes shifts of 15100-20260 cm(-1) and quantum yields (Φ(F)) of up to 65% in the solid state. The low-energy fluorescence emission, which was assigned to a charge-transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C-C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660-18090 cm(-1) for the CT bands and 1960-5540 cm(-1) for the high-energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ(F) values between 8-32%. Two distinct excited singlet-state (S(1)) geometries, denoted S(1)(LE) and S(1)(CT), were observed computationally for the benzodiazaborolyl-ortho-carboranes, the population of which depended on their orientation (ψ). TD-DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C-diazaborolyl-ortho-carboranes were viewed as donor-acceptor systems with the diazaborolyl group as the donor and the ortho-carboranyl group as the acceptor.

Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. and on the diazaborolyl group in 1-4 whereas the LUMOs are largely aryl in character for all compounds. Thus, in contrast to other conjugated systems containing three-coordinate boron centers such as B(Mes) 2 , (Mes = 2,4,6-Me 3 C 6 H 2 ), in which the boron serves as a π-acceptor, the 10-π electron benzodiazaborole moiety appears to function as a π-donor moiety.

. (2013) 'Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes.', Dalton transactions., 42 (6). pp. 2266-2281.Further information on publisher's website:http://dx.doi.org/10.1039/c2dt32378hPublisher's copyright statement: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractFifteen C-diazaborolyl-ortho-carboranes, 1-R ′ -2-R ″ -1,2-C 2 B 10 H 10 , where R′ represents the groups 2-(1,3-Et 2 -1,3,2-N 2 BC 6 H 4 )-, 2-(1,3-Ph 2 -1,3,2-N 2 BC 6 H 4 )-, 2-(1,3-Ph 2 -5,6-Me 2 -1,3,2-N 2 BC 6 H 2 )-, 2-(1,3-i Pr 2 -1,3,2-N 2 BC 6 H 4 )-, and 2-(1,3,2-N 2 BC 6 H 6 )-and where R ″ equals to H, Me, Ph, t Bu or SiMe 3 were synthesized. Cyclovoltammetric studies of the compounds showed irreversible oxidation waves which are caused by the oxidation of the heterocycle. Those C-diazaborolyl-ortho-carboranes with Ph, tBu SiMe 3 substituents at the adjacent C-atom of the cage displayed two one-electron reduction waves reflecting the formation of stable radical monoanions with unusual (2n+3) skeletal electron counts. The geometries of these anions were determined by combinations of infrared, UV-visible spectroelectrochemical and computational studies. Additionally the structures of seven new C-diazaborolyl-ortho-carboranes and one new 2-bromo-1,3,2-benzodiazaborole were determined by X-ray crystallography and compared with previously obtained structures.

New operating regimes for engines and combustors and the advocated use of non-conventional transportation fuels demand investigation of the combustion chemistry of different classes of chemicals, especially under premixed conditions. Detailed species compositions during combustion are needed to estimate hazardous emissions, and models for their prediction must be validated for the intended combustion conditions.Molecular-beam mass spectrometry (MBMS) is a common technique to measure quantitative species concentrations in flames. It is widely employed to characterize the flame chemistry of laminar premixed combustion, and it has been complemented with optical measurements for the detection of a number of molecular species and radicals. Significant progress has been made in recent studies through the introduction of synchrotron-based MBMS instruments. They have improved the identification process by using tunable vacuum-ultraviolet radiation for photoionization of the species to be detected, and isomer-specific measurements are now almost routinely possible. Along with quantitative species measurements, the temperature profile is needed as input parameter for chemical kinetic modeling. It is usually determined either using thermocouples or laser spectroscopic techniques.It is an ongoing discussion how sampling probes affect these measurements, and how MBMS results can be compared to combustion modeling. The present article is intended to contribute to this discussion by providing optical and MBMS results obtained with several sampling configurations.