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Molecular mobility in self-assembled dendritic chromophore glasses
Daniel B Knorr1, Xing-Hua Zhou, Zhengwei Shi
1Department of Chemical Engineering, University of Washington, Seattle, Washington 98115-1750, USA.
The Journal of Physical Chemistry. B
|September 29, 2009
Summary
Designing advanced nonlinear optical materials requires understanding molecular relaxation. This study reveals optimal conditions for poling self-assembling molecular glasses by analyzing their enthalpic and entropic relaxation modes.
Area of Science:
- Materials Science
- Chemistry
- Physics
Background:
- Designing complex amorphous structures, particularly organic nonlinear optical (NLO) materials, necessitates integrated cognitive approaches combining synthesis, analysis, and simulation.
- Self-assembling molecular glasses with dendritic stabilization moieties (phenyl, naphthyl, anthryl) are candidates for high electro-optical activity (>300 pm/V).
Purpose of the Study:
- To investigate the molecular enthalpic and entropic relaxation modes in self-assembling molecular glasses using nanoscale thermo-mechanical analyses.
- To correlate these relaxation modes with the efficiency of electric field poling for optimizing NLO material properties.
Main Methods:
- Nanoscale thermo-mechanical analyses to probe molecular relaxation.
- Intrinsic friction microscopy (IFA) for energetic analyses.
- Molecular dynamic simulations to understand activation energy origins.
Main Results:
- Identified three phase relaxation regimes governed by arene-perfluoroarene interactions during self-assembly.
- Intermediate relaxation regimes (8-15°C width, 40-60 kcal/mol activation energy) are most effective for poling.
- Temporal stability increases with arene size in the low-temperature regime; poling efficiency is inversely related to entropic contributions in the high-temperature regime.
Conclusions:
- The study provides direct insight into molecular relaxation mechanisms influencing NLO material performance.
- Understanding and controlling relaxation regimes are crucial for optimizing poling efficiency and temporal stability.
- Activation energies below the glass transition temperature are primarily linked to noncovalent interactions between molecular moieties.
