![]() ![]() ![]() We use a combination of steady-state and femtosecond transient absorption and emission spectroscopies to globally fit the multiple electronic transitions underlying the spectra of both the “closed” and “open” conformers, which agree well with the TD-DFT calculations. Temperature-dependent experiments and the TD-DFT calculations indicate that the “closed” conformer is ∼70 meV more stable than the “open” conformer, so that both conformers are important to the behavior of the molecule at room temperature and above. Given the extent of through-space and through-bond coupling, however, neither di-PDI conformer can be well described simply in terms of independently coupled monomers instead, a full quantum chemistry description is required to understand the electronic structure of this molecule. These conformations are an “open” geometry, where the two monomer subunits are oriented nearly at right angles, giving them more J-like coupling, and a “closed” geometry, in which the two monomer subunits are nearly π-stacked, resulting in a more H-like coupling. Excitation–emission spectroscopy reveals two distinct emitting species, which are further characterized by time-dependent density functional theory (TD-DFT), demonstrating that the bay-linked PDI dimers exist in two geometrical conformations. Bay-linked diperylenediimide (di-PDI) molecules are finding increasing use in organic electronics because of their steric hindrance that “twists” the two monomer units relative to one another, decreasing molecular aggregation. ![]()
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