Molecular crystals are a class of solids that have applications in organic LEDs, lasers, and solar cells, and optical absorption is among their most important properties. The optical absorption behaviour can be strongly affected by changes in the conformation or packing of the molecule, leading to phenomena such as colour polymorphism, where the same molecule can form different crystal structures that have different colours.
As described in a paper in the Journal of Chemical Theory and Computation, we developed a ‘crystal spectral warping’ method that allows the accurate and efficient prediction of optical absorption spectra of molecular crystals, including both long-range interactions, and the accuracy of hybrid TDDFT calculations. We applied this approach to the well-known colour polymorphic system ROY, and showed that our results give a better description of experimental observations than previous attempts.
J. C. A. Prentice and A. A. Mostofi, Accurate and efficient computation of optical absorption spectra of molecular crystals: the case of the polymorphs of ROY, Journal of Chemical Theory and Computation 17, 5214 (2021).