Large-Amplitude Charge Relocation in a Vibrationally Excited Molecular Crystal Probed by Femtosecond X-ray
Isabel Gonzalez-Vallejo1, Azize Koc1, Janett Feickert1
1Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany.
Femtosecond X-ray diffraction revealed how charge redistributes within and between molecules in crystalline 4-(diisopropylamino)benzonitrile (DIABN). The crystal lattice oscillates out of phase with molecular charge, influencing macroscopic electric polarization.
Area of Science:
- Physical Chemistry
- Materials Science
- Spectroscopy
Background:
- Charge transfer dynamics are crucial for molecular materials but often poorly understood at the molecular level.
- Experimental probes of time-dependent charge distributions are needed to elucidate these processes.
Purpose of the Study:
- To map transient charge distributions in polycrystalline 4-(diisopropylamino)benzonitrile (DIABN) using femtosecond X-ray powder diffraction.
- To understand the interplay between electronic and nuclear degrees of freedom governing charge transfer.
Main Methods:
- Femtosecond X-ray powder diffraction was employed to probe DIABN.
- Excitation of the C≡N stretching vibration initiated charge relocation dynamics.
Main Results:
- Oscillatory intramolecular charge relocations were observed, driven by low-frequency crystal lattice displacements.
- The crystalline environment exhibited out-of-phase charge oscillations to minimize electrostatic energy.
- Soft-mode behavior impacting macroscopic electric polarization was identified.
Conclusions:
- Femtosecond X-ray diffraction provides unprecedented insight into molecular-level charge dynamics in crystals.
- Intermolecular coupling significantly influences charge transfer and macroscopic polarization in DIABN.
- Understanding these dynamics is key for designing advanced molecular electronic materials.
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