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

This work probes the dynamics of intramolecular charge transfer in a pentacene-diketopyrrolopyrrole dyad. Detailed ultrafast spectroscopic analysis reveals that charge transfer depends on the rotational conformer excited, reflecting strong heterogeneity in intramolecular electronic couplings. Exciting with different pump wavelengths can yield a short-lived, dark charge-transfer state; a long-lived, bright charge-transfer state; or no energy or charge transfer at all.

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.

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