TY - JOUR A1 - Pecqueur, Sébastien A1 - Maltenberger, Anna A1 - Petrukhina, Marina A. A1 - Halik, Marcus A1 - Jaeger, Arndt A1 - Pentlehner, Dominik A1 - Schmid, Günter T1 - Bismut-haltige p-Dotanden mit großer Bandlücke für optoelektronische Anwendungen JF - Angewandte Chemie N2 - Zehn neue p‐Dotanden für die Leitfähigkeitsdotierung von organischen Halbleitern wurden identifiziert. Der wesentliche Vorteil der elektrophilen Tris(carboxylato)‐Bismut(III)‐Verbindungen ist die niedrige Absorption der damit dotierten Schichten. Diese Eigenschaft zusammen mit ihren niedrigen Herstellungskosten sowie der guten Verdampfbarkeit und Stabilität macht diese Dotanden sehr attraktiv für Anwendungen in der organischen Elektronik. KW - p-Dotanden KW - Organische Halbleiter KW - Bismut Y1 - 2016 IS - 128(35) PB - Wiley-VCH Verlag CY - Weinheim ER - TY - JOUR A1 - Pecqueur, Sébastien A1 - Maltenberger, Anna A1 - Petrukhina, Marina A. A1 - Halik, Marcus A1 - Jaeger, Arndt A1 - Pentlehner, Dominik A1 - Schmid, Günter T1 - Wide Band-Gap Bismuth-based p-Dopants for Opto-Electronic Applications JF - Angewandte Chemie International Edition N2 - Ten new efficient p‐dopants for conductivity doping of organic semiconductors for OLEDs are identified. The key advantage of the electrophilic tris(carboxylato) bismuth(III) compounds is the unique low absorption of the resulting doped layers which promotes the efficiency of OLED devices. The combination of these features with their low fabrication cost, volatility, and stability, make these materials very attractive as dopants in organic electronics. KW - p-Dopants KW - Bismuth KW - OLED Y1 - 2016 IS - 55 PB - Wiley-VCH Verlag CY - Weinheim ER - TY - JOUR A1 - Christiansen, Lars A1 - Nielsen, Jens H. A1 - Christensen, Lauge A1 - Shepperson, Benjamin A1 - Pentlehner, Dominik A1 - Stapelfeldt, Henrik T1 - Laser-induced Coulomb explosion of 1,4–diiodobenzene molecules: Studies of isolated molecules and molecules in helium nanodroplets JF - Physical Review A N2 - Coulomb explosion of 1,4–diiodobenzene molecules, isolated or embedded in helium nanodroplets, is induced by irradiation with an intense femtosecond laser pulse. The recoiling ion fragments are probed by time-of-flight measurements and two-dimensional velocity map imaging. Correlation analysis of the emission directions of I+ ions recoiling from each end of the molecules reveals significant deviation from axial recoil, i.e., where the I+ ions leave strictly along the I-I symmetry axis. For isolated molecules, the relative angular distribution of the I+ ions is centered at 180∘, corresponding to perfect axial recoil, but with a full width at half maximum of 30∘. For molecules inside He droplets, the width of the distribution increases to 45∘. These results provide a direct measure of the accuracy of Coulomb explosion as a probe of the spatial orientation of molecules, which is particularly relevant in connection with laser-induced molecular alignment and orientation. In addition, our studies show how it is possible to identify fragmentation pathways of the Coulomb explosion for the isolated 1,4–diiodobenzene molecules. Finally, for the 1,4–diiodobenzene molecules in He droplets, it is shown that the angular correlation between fragments from the Coulomb explosion is preserved after they have interacted with the He environment. KW - Isolated Molecules KW - Helium nanodroplets KW - Coulomb explosion Y1 - 2016 IS - 93 ER - TY - JOUR A1 - Christiansen, Lars A1 - Nielsen, Jens H. A1 - Pentlehner, Dominik A1 - Underwood, Jonathan G. A1 - Stapelfeldt, Henrik T1 - Alignment enhancement of molecules embedded in helium nanodroplets by multiple laser pulses JF - Physical Review A N2 - We show experimentally that field-free one-dimensional (1D) alignment of 1,4-diiodobenzene molecules embedded in helium nanodroplets, induced by a single, linearly polarized 200-fs laser pulse, can be significantly enhanced by using two or four optimally synchronized laser pulses. The strongest degree of 1D alignment is obtained with four pulses and gives ⟨cos2θ⟩>0.60. Besides the immediate implications for molecular frame studies, our results pave the way for more general manipulation of rotational motion of molecules in He droplets. KW - Isolated Molecules KW - Helium nanodroplets Y1 - 2015 IS - 92 ER - TY - JOUR A1 - Pentlehner, Dominik A1 - Slenczka, Alkwin T1 - Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets JF - The Journal of Chemical Physics N2 - Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm−1) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time. KW - Superfluid helium nanodroplets KW - Anthracene derivates Y1 - 2015 IS - 142 ER - TY - JOUR A1 - Premke, Tobias A1 - Wirths, Eva-Maria A1 - Pentlehner, Dominik A1 - Riechers, Ricarda A1 - Lehnig, Rudolf A1 - Vdovin, Alexander A1 - Slenczka, Alkwin T1 - Microsolvation of molecules in superfluid helium nanodroplets revealed by means of electronic spectroscopy JF - Frontiers in Chemistry N2 - The empirical model explaining microsolvation of molecules in superfluid helium droplets proposes a non-superfluid helium solvation layer enclosing the dopant molecule. This model warrants an empirical explanation of any helium induced substructure resolved for electronic transitions of molecules in helium droplets. Despite a wealth of such experimental data, quantitative modeling of spectra is still in its infancy. The theoretical treatment of such many-particle systems dissolved into a quantum fluid is a challenge. Moreover, the success of theoretical activities relies also on the accuracy and self-critical communication of experimental data. This will be elucidated by a critical resume of our own experimental work done within the last ten years. We come to the conclusion that spectroscopic data and among others in particular the spectral resolution depend strongly on experimental conditions. Moreover, despite the fact that none of the helium induced fine structure speaks against the empirical model for solvation in helium droplets, in many cases an unequivocal assignment of the spectroscopic details is not possible. This ambiguity needs to be considered and a careful and critical communication of experimental results is essential in order to promote success in quantitatively understanding microsolvation in superfluid helium nanodroplets. KW - Microsolvation of molecules KW - Helium nanodroplets KW - Electronic spectroscopy Y1 - 2014 VL - 2014 IS - 2 ER - TY - JOUR A1 - Hansen, Jonas A1 - Omiste, Juan J. A1 - Nielsen, Jens H. A1 - Pentlehner, Dominik A1 - Küpper, Jochen A1 - González-Férez, Rosario A1 - Stapelfeldt, Henrik T1 - Mixed-field orientation of molecules without rotational symmetry JF - The Journal of Chemical Physics N2 - The mixed-field orientation of an asymmetric-rotor molecule with its permanent dipole moment nonparallel to the principal axes of polarizability is investigated experimentally and theoretically. We find that for the typical case of a strong, nonresonant laser field and a weak static electric field complete 3D orientation is induced if the laser field is elliptically polarized and if its major and minor polarization axes are not parallel to the static field. For a linearly polarized laser field solely the dipole moment component along the most polarizable axis of the molecule is relevant resulting in 1D orientation even when the laser polarization and the static field are nonparallel. Simulations show that the dipole moment component perpendicular to the most-polarizable axis becomes relevant in a strong dc electric field combined with the laser field. This offers an alternative approach to 3D orientation by combining a linearly polarized laser field and a strong dc electric field arranged at an angle equal to the angle between the most polarizable axis of the molecule and its permanent dipole moment. KW - Asymmetric-rotor molecule KW - Mixed-field orientation Y1 - 2013 IS - 139 ER - TY - JOUR A1 - Riechers, Rudolf A1 - Pentlehner, Dominik A1 - Slenczka, Alkwin T1 - Microsolvation in superfluid helium droplets studied by the electronic spectra of six porphyrin derivatives and one chlorine compound JF - The Journal of Chemical Physics N2 - After almost two decades of high resolution molecular spectroscopy in superfluid helium droplets, the understanding of microsolvation is still the subject of intense experimental and theoretical research. According to the published spectroscopic work including microwave, infrared, and electronic spectroscopy, the latter appears to be particularly promising to study microsolvation because of the appearance of pure molecular transitions and spectrally separated phonon wings. Instead of studying the very details of the influence of the helium environment for one particular dopant molecule as previously done for phthalocyanine, the present study compares electronic spectra of a series of non-polar porphyrin derivatives when doped into helium droplets consisting of 104–105 helium atoms. Thereby, we focus on the helium-induced fine structure, as revealed most clearly at the corresponding electronic origin. The interpretation and the assignment of particular features obtained in the fluorescence excitation spectra are based on additional investigations of dispersed emission spectra and of the saturation behavior. Besides many dopant-specific results, the experimental study provides strong evidence for a particular triple peak feature representing the characteristic signature of helium solvation for all seven related dopant species. KW - Superfluid helium droplets KW - Porphyrin derivatives KW - Chlorine compound Y1 - 2013 IS - 138 ER - TY - JOUR A1 - Pentlehner, Dominik A1 - Nielsen, Jens H. A1 - Christiansen, Lars A1 - Slenczka, Alkwin A1 - Stapelfeldt, Henrik T1 - Laser Induced Adiabatic Alignment of Molecules Dissolved in Helium Nanodroplets JF - Physical Review A N2 - A moderately intense, nonresonant, linearly polarized nanosecond laser pulse is used to induce one-dimensional (1D) adiabatic alignment of 1,4 diiodobenzene (C6H4I2), iodobenzene (C6H5I), and methyliodide (CH3I) molecules dissolved in helium nanodroplets. The alignment sharpens as the laser intensity is increased, similar to the behavior in gas phase. For diiodobenzene the highest degree of alignment, ⟨cos2θ2D⟩=0.90, is essentially identical to the value obtained for isolated molecules in a supersonic beam, whereas the highest degrees of alignment for iodobenzene and for methyliodide in helium droplets fall below the values obtained for isolated molecules. We believe this is due to the deviation from axial recoil in the Coulomb explosion process that probes the alignment of the molecules in the He droplets. KW - Helium nanodroplets KW - Linearly polarized nanosecond laser pulse Y1 - 2013 IS - 87 ER - TY - JOUR A1 - Pentlehner, Dominik A1 - Nielsen, Jens H. A1 - Slenczka, Alkwin A1 - Mølmer, Klaus A1 - Stapelfeldt, Henrik T1 - Impulsive Laser Induced Alignment of Molecules Dissolved in Helium Nanodroplets JF - Physical Review Letters N2 - We show that a 450 fs nonresonant, moderately intense, linearly polarized laser pulse can induce field-free molecular axis alignment of methyliodide (CH3I) molecules dissolved in a helium nanodroplet. Time-resolved measurements reveal rotational dynamics much slower than that of isolated molecules and absence of the sharp transient alignment recurrences characteristic of gas phase molecules. Our results presage a range of new opportunities for exploring both molecular dynamics in a dissipative environment and the properties of He nanodroplets. KW - Helium nanodroplets KW - mpulsive Laser Induced Alignment Y1 - 2013 IS - 110 ER -