The optical rotation of chiral compounds was discovered over two centuries ago, and yet nobody can infer the sign and magnitude of the optical rotation of linearly polarized light induced by an optically active sample only by looking at its molecular structure. We have developed a method to analyze the origin of molecular optical activity in terms of orbital contributions and rotatory strength in configuration space. The method uses quantities already available at completion of standard linear-response calculations of specific rotation, and it requires minimal manipulation. A preliminary application to (1S,4S)-norbornenone and (P)-2,3-pentadiene shows that only a few orbitals contribute significantly to the specific rotation, and they can be used directly for a qualitative interpretation of this fundamental property. We also explore whether canonical or localized orbitals provide a better framework for the interpretation of the specific rotation of a chiral molecule. We focus in particular on helicenes, which are a class of molecules with particularly large specific rotation. We consider helicenes of increasing size, and with various choices of substituent groups, to study how the chiroptical response of these compounds can be tuned. Furthermore, we investigate how the optical rotation is influenced by intermolecular interactions in solid materials, using chains of diatomic molecules oriented in a helical pattern as a proxy for chiral supramolecular materials. Since this is an oriented system, we are able to analyze how the individual components of the response tensor associated with optical rotation vary with system size and relative orientation of the constituent molecular units.<br/>

Characterization of the optical rotation in molecules and extended 1D systems

2019 Spring National Meeting

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