Conformational Heterogeneity Governs Charge Transfer Pathways in a Pentacene-Diketopyrrolopyrrole Dyad

Understanding how conformational disorder influences relaxation pathways is essential for the rational design of molecular donor-acceptor systems. In this work, the authors investigate the role of conformational heterogeneity on intramolecular charge transfer in a covalently linked donor-acceptor dyad (P-D). Using excitation energy dependent transient absorption and photoluminescence spectroscopy in various solvents, the authors find that stabilized planar conformers exhibit ultrafast intramolecular hole transfer to form a short lived, dark charge transfer state originating from band-edge excitation. Destabilized twisted conformers excited at higher energies yield long-lived, emissive charge transfer states. These findings demonstrate how wide variations in intramolecular coupling within a single molecule can result in entirely different relaxation pathways. Furthermore, the authors emphasize the importance of considering conformational heterogeneity when studying molecular dimers for optoelectronic processes necessary for future applications.