Unraveling the sources of broadening in UV-Visible spectra of crystalline oligoacenes using multiscale computational protocols

Organic molecular crystals have gained significant research attention in recent years due to their intriguing pho- tophysical properties and potential applications in photovoltaic and emissive devices. This growing interest has amplified the need for accurate and robust computational protocols to investigate their photophysical behavior. In this work, we present multiscale computational strategies designed to model the shape and broadening of UV-Vis absorption spectra in organic crystalline materials. These protocols enable a quantitative assessment of spectral broadening originating from various sources in typical crystalline polyacenes. Adopting an ab initio approach, we employ self-consistent microelectrostatic embedding and Ewald-based ONIOM models to incor- porate structural features and environmental effects, as well as contributions from static disorder, excitonic coupling, and vibronic interactions. The developed protocols successfully quantify the spectral broadening, as demonstrated for naphthalene and anthracene crystals. This framework is broadly applicable and offers a reliable foundation for the investigation of a wide range of organic molecular crystals, enabling detailed studies of diverse fluorophores and systems of photophysical relevance.