posted on 2024-02-05, 18:41authored byRichard
L. Puro, Thomas P. Gray, Tsitsi A. Kapfunde, George B. Richter-Addo, Markus B. Raschke
Coupling
between molecular vibrations leads to collective vibrational
states with spectral features sensitive to local molecular order.
This provides spectroscopic access to the low-frequency intermolecular
energy landscape. In its nanospectroscopic implementation, this technique
of vibrational coupling nanocrystallography (VCNC) offers information
on molecular disorder and domain formation with nanometer spatial
resolution. However, deriving local molecular order relies on prior
knowledge of the transition dipole magnitude and crystal structure
of the underlying ordered phase. Here we develop a quantitative model
for VCNC by relating nano-FTIR collective vibrational spectra to the
molecular crystal structure from X-ray crystallography. We experimentally
validate our approach at the example of a metal organic porphyrin
complex with a carbonyl ligand as the probe vibration. This framework
establishes VCNC as a powerful tool for measuring low-energy molecular
interactions, wave function delocalization, nanoscale disorder, and
domain formation in a wide range of molecular systems.