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Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and
Voigt-Martin1, Kothe, Yakimansky
1Institut fur Physikalische Chemie der Johannes Gutenberg Universitat, Mainz, Germany.
Ultramicroscopy
|May 11, 2000
Summary
Researchers synthesized 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), a molecule with high second-order non-linear optical (NLO) coefficients. Electron diffraction and quantum-chemical calculations determined its structure and NLO properties for material optimization.
Area of Science:
- Materials Science
- Crystallography
- Quantum Chemistry
Background:
- Intramolecular two-dimensional charge transfer molecules are synthesized for advanced optical applications.
- Relating molecular hyperpolarizability to bulk NLO properties requires precise crystal structure determination.
- X-ray crystallography is often limited by the difficulty of growing suitable single crystals.
Purpose of the Study:
- To determine the crystal structure of 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC) using electron diffraction.
- To calculate the non-linear optical (NLO) properties of DMABC at both molecular and bulk levels.
- To establish a relationship between molecular hyperpolarizability and macroscopic NLO coefficients.
Main Methods:
- Crystal structure analysis via electron diffraction, supported by simulation and statistical methods (maximum entropy, log likelihood).
- High-voltage (300 kV) electron diffraction data acquisition using an on-line CCD camera, compared with 100 kV film-based data.
- Quantum-chemical calculations (ab initio and semi-empirical) to determine NLO susceptibility tensor components.
Main Results:
- Successful structural analysis of DMABC was achieved using electron diffraction, overcoming limitations of single crystal growth.
- Electron diffraction with a CCD camera provided improved resolution and dynamic range compared to film-based methods.
- Calculated NLO susceptibility tensor components were successfully related to the macroscopic quadratic non-linearity tensor of the crystal.
Conclusions:
- Electron diffraction is a viable alternative to X-ray diffraction for structural analysis of NLO materials when single crystals are difficult to obtain.
- The study provides a method to link molecular-level NLO properties to bulk crystalline behavior.
- DMABC exhibits significant potential for applications requiring high second-order NLO coefficients.