Electron Delocalization in Carbonyl-Functionalized Ladder-Type Oligo(p-Phenylene)s

Carbonyl groups are often found in promising Donor-Acceptor-type conjugated polymers like naphthalene diimide (NDI), perylenediimide (PDI), and diketopyrrolopyrrole (DPP) and many other which serve as acceptor units in organic solar cells (OSCs). It is important to understand how electrons and holes spatially and temporally behave in organic conjugated molecules along with localization and delocalization influences on the efficiencies of OSCs. We hypothesize that we can use a carbonyl group as an infrared reporter to better understand the nature and behavior of charges in such molecules. Their usage to probe charges and excitons has remained largely underexplored. We design and synthesize a series of carbonyl-functionalized ladder-type oligo(p-phenylene)s (LnPCHO, n = 3, 4, 5, 6). These oligomers are rigidified with two to five bridges for maximum _-conjugation and flatness. The pendant hexyl side chains increase the solubility of the molecules, and carbonyl group allows for a sensitive real-time detection of the dynamics of electron delocalization - by time-resolved infrared spectroscopy followed by pulse radiolysis. Herein, we present our multi-step organic syntheses for the target molecules and talk about our future work.