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Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

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Negative Nonlinear CD-ee Dependence in Polycrystalline BINOL Thin Films.

Kevin Liang¹, Florian Ristow², Kevin Li¹

¹Catalysis Research Center and School of Natural Sciences, Chair of Physical Chemistry, Technische Universität München, Lichtenbergstraße 4, 85748 Garching, Germany.

Journal of the American Chemical Society

|December 13, 2023

Summary

This summary is machine-generated.

Researchers observed rare negative nonlinear behavior in circular dichroism-enantiomeric excess (CD-ee) dependence using BINOL polycrystalline films. This finding offers new possibilities for precise enantiomeric excess characterization in chiral systems.

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Area of Science:

Chiroptical Spectroscopy
Supramolecular Chemistry
Materials Science

Background:

The relationship between circular dichroism (CD) and enantiomeric excess (ee) in chiral systems is typically linear.
Nonlinear CD-ee dependence, especially negative nonlinear (NN) behavior, is uncommon and poorly understood.

Purpose of the Study:

To investigate and characterize strong negative nonlinear CD-ee dependence in polycrystalline BINOL thin films.
To elucidate the underlying mechanisms driving this observed phenomenon.

Main Methods:

Second-harmonic-generation circular dichroism (SHG-CD) spectroscopy
Commercial CD spectroscopy
Theoretical calculations
Microscopy
Fourier-transform infrared (FTIR) spectroscopy

Main Results:

Demonstrated a strong negative nonlinear CD-ee dependence in BINOL polycrystalline thin films.
Attributed the NN behavior to alterations in the supramolecular chirality of the BINOL system.
Provided evidence supporting the potential for NN CD-ee dependence in racemate crystals.

Conclusions:

Negative nonlinear CD-ee dependence in chiral systems is achievable and linked to supramolecular chirality.
This phenomenon holds significant potential for enhancing the accuracy of enantiomeric excess characterization.
The findings open avenues for optimizing enantioselective separation, catalysis, and chiral sensing technologies.