Quantum chemical modeling of the spectral properties of oligofluorenes.

[Display omitted] • S0 → S1 electron excitation in polyfluorene in most cases is localized in central 8–9 units. • Changing conformation may lead to small changes of effective conjugation length. • Substituents in side radicals do not have a significant effect on the localization of excitation. This study investigates the excited states within oligomeric fluorene compounds containing up to 20 monomer units in various conformations. Furthermore, it explores the impact of donor and acceptor substituents in the side chain. Time-dependent density functional theory (TD-DFT) simulations were conducted at the B3LYP/def2-svp level of theory. Results indicate localized excitation, primarily spanning 8–13 monomer units, irrespective of donor and acceptor substituents. These findings offer insights into charge carrier mobility, electroluminescent properties of polyfluorenes, and facilitate the design of novel materials within this class. [ABSTRACT FROM AUTHOR]