Many functional properties of molecular systems sensitively depend the local chemical environment seen by each molecule. In that regard, intermolecular coupling plays a pivotal role in controlling energy and charge transfer on molecular length scales. However, determining molecular structure and disorder and with nanometer resolution has notoriously been difficult. Conventional crystallography techniques based on the diffraction of high energy photons and electrons are not sensitive to this low-frequency intermolecular energy landscape.
STROBE teams have recently demonstrated that coupling between molecular vibrations and the resulting collective vibrational states have spectral features that allows one to derive not only the local molecular disorder and nano-scale domain formation, but also enables spectroscopic access to the low-frequency intermolecular energy landscape itself. The spatio-spectral nano-imaging of these collective vibrations in IR nano-spectroscopy has provided a new crystallography technique of vibrational coupling nano-crystallography (VCNC), which offers information on molecular order, disorder, and defects with nano-scale resolution.
In the new work, a STROBE team from CU Boulder collaborating with scientists from the University of Oklahoma now provides a solid theoretical foundation and benchmark measurements to make VCNC quantitative and predictive. This work advances VCNC from a qualitative tool capable of measuring changes in local molecular order to a quantitative technique able to measure and image precise vibrational wavefunction delocalization lengths and intermolecular interaction distances. The technique can now be applied to a wide range of functional molecular systems to image molecular order and disorder on their fundamental length scales.