Energy Flow Dynamics within Cofacial and Slip-Stacked Perylene-3,4-dicarboximide Dimer Models of π-Aggregates

Robust perylene-3,4-dicarboximide (PMI) π-aggregates provide important light-harvesting and electron–hole pair generation advantages in organic photovoltaics and related applications, but relatively few studies have focused on the electronic interactions between PMI chromophores. In contrast, structure–function relationships based on π–π stacking in the related perylene-3,4:9,10-bis(dicarboximides) (PDIs) have been widely investigated. The performance of both PMI and PDI derivatives in organic devices may be limited by the formation of low-energy excimer trap states in morphologies where interchromophore coupling is strong. Here, five covalently bound PMI dimers with varying degrees of electronic interaction were studied to probe the relative chromophore orientations that lead to excimer energy trap states. Femtosecond near-infrared transient absorption spectroscopy was used to observe the growth of a low-energy transition at ∼1450–1520 nm characteristic of the excimer state in these covalent dimers. The ...