| 1. |
- Guarnaccio, Ambra, et al.
(author)
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PPT Isolated Molecule and Its Building Block Moieties Studied by C 1s and O 1s Gas Phase X-ray Photoelectron and Photoabsorption Spectroscopies
- 2020
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In: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:18, s. 9774-9786
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Journal article (peer-reviewed)abstract
- The present study is focused on the comprehensive gas phase electronic structure characterization of 2,8-bis-(diphenylphosphoryl)-dibenzo[b,d]thiophene (PPT), a promising ambipolar phosphorescent host material recently introduced in organic light-emitting diodes (OLEDs). This molecular system can be considered ideally formed by two diphenylphosphine oxide (dPPO) moieties functionalizing the small dibenzothiophene (DBT) core. PPT is characterized by high triplet energy and is known as good vacuum sublimable electron transporting material for blue OLEDs. The triphenyl phosphine oxide (TPPO) molecule has been chosen as the model compound of the dPPO groups in PPT. A combined experimental and theoretical study by density functional theory of the gas phase electronic structure of TPPO and PPT has been performed through X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy measured at the carbon and oxygen is regions. The study represents a detailed characterization of the impact of the single building blocks on the electronic structure of the whole PPT molecule. Moreover, it confirms that the phosphine oxide groups act as breaking points of the pi-conjugation between the DBT core of PPT and the outer groups, leaving the electronic structures of the compound practically matching those of the central DBT moiety.
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| 2. |
- Kumar Maroju, Praveen, et al.
(author)
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Attosecond pulse shaping using a seeded free-electron laser
- 2020
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 578, s. 386-391
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Journal article (peer-reviewed)abstract
- Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters, multilayer mirrors and manipulation of the driving field. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers.
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| 3. |
- Maroju, Praveen K., et al.
(author)
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A Novel Attosecond Timing Tool for Free-Electron Laser Experiment
- 2020
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In: High Intensity Lasers and High Field Phenomena 2020. - 9781943580736
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Conference paper (peer-reviewed)abstract
- We demonstrate a novel timing tool for Free-Electron Lasers to determine the delay between an attosecond pulse train and infrared pulse with sub-optical-cycle resolu-. tion.
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