We propose a new approach for calculating the change of the absorption spectrum of a molecule when moved from the gas phase to a crystalline morphology. The so-called gas-to-crystal shift Δ[Formula: see text] is mainly caused by dispersion effects and depends sensitively on the molecule's specific position in the nanoscopic setting. Using an extended dipole approximation, we are able to divide Δ[Formula: see text] = - in two factors, where depends only on the molecular species and accounts for all nonresonant electronic transitions contributing to the dispersion while is a geometry factor expressing the site dependence of the shift in a given molecular structure. The ability of our approach to predict absorption spectra is demonstrated using the example of polycrystalline films of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI).

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4360364PMC
http://dx.doi.org/10.1021/acs.jpcc.5b01587DOI Listing

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