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Surface enhanced second harmonic generation from macrocycle, catenane, and rotaxane thin films: experiments and
Imad Arfaoui1, Verónica Bermúdez, Giovanni Bottari
1Materials Science Centre, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands.
The Journal of Physical Chemistry. B
|April 14, 2006
Summary
Surface enhanced second harmonic generation (SE SHG) experiments reveal ordered thin films of molecular structures on silver. Calculations accurately predict the nonlinear optical properties of rotaxane thin films, showing excellent agreement with experimental results.
Area of Science:
- Nonlinear optics
- Surface science
- Materials chemistry
Background:
- Surface-enhanced second harmonic generation (SE SHG) is a sensitive technique for probing molecular organization.
- Ordered thin films are crucial for advanced optical and electronic applications.
- Understanding molecular ordering and nonlinear optical properties is key to designing novel materials.
Purpose of the Study:
- To investigate the thin film formation and SE SHG properties of molecular structures, macrocycles, catenanes, and rotaxanes.
- To interpret SE SHG activity in terms of electric field induced second harmonic (EFISH) generation.
- To compare experimental nonlinear optical susceptibility with theoretical calculations.
Main Methods:
- Vacuum sublimation of molecular structures onto silver substrates.
- Surface-enhanced second harmonic generation (SE SHG) measurements.
- Molecular mechanics/dynamics simulations (TINKER) and electric field calculations (Delphi4).
Main Results:
- Molecules formed ordered thin films, with macrocycle monolayers exhibiting the highest order and rotaxane multilayers the lowest.
- SE SHG activity was attributed to EFISH generation, driven by silver substrate atoms.
- Calculated SHG susceptibilities showed excellent agreement with experimental measurements for rotaxane thin films.
Conclusions:
- Vacuum-sublimated molecular structures form ordered thin films on silver surfaces.
- The EFISH model accurately describes the SE SHG response of these molecular films.
- This study validates the combined experimental and computational approach for characterizing nonlinear optical properties of molecular materials.
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