Materials capable of efficient charge separation and the generation of manipulable radicals are essential for innovative applications in photovoltaics and photocatalysis, but also spintronics. Organic semiconductors are increasingly recognized as promising candidates for these technologies, primarily due to their high polarizability and low spin-orbit coupling. However, these advantages are often offset by the propensity for fast recombination of charge carriers, driven by their low dielectric constants and strong Coulombic interactions, which can severely limit device performance. To address these challenges, it is crucial to identify key parameters in material design that improve energy and electron transfer between pi-conjugated molecules or stabilize charge-separated (CS) states in donor-acceptor systems.

In our laboratory, we developed a versatile supramolecular approach using chromophores disubstituted with chiral oligopeptide-polymer chains to form helical, singular molecular stacks.¹ Notably, the photogeneration of charges persisting for days was observed in some of these strictly one-dimensional assemblies, including thiophene and dicyanoperylene bisimide derivatives.^2,3

In this work, we report on the investigation of the reasons for the stability of these charges in the dicyanoperylene bisimide-based nanowires. The study integrates experimental, computational, and theoretical approaches, offering a comprehensive insight into the photophysical properties of these nanowires. We demonstrate that spin-decorrelated CS states can be stabilized within covalent donor-acceptor entities through supramolecular assembly while nonetheless maintaining a degree of structural flexibility that enables critical intermolecular vibronic interactions supporting the longevity of the CS state.

We found that the anionic radical dicyanoperylene bisimides observed within the strongly excitonically coupled nanowires emerged from self-doping via a charge separation between the core and the substituents. This electron transfer reaction is achievable not only by photoexcitation but also thermally, leading to a permanently measurable population of radicals by steady-state spectroscopies, and the photomodulability of the radical concentration, thanks to kinetic trapping of excess population. The stability of some polarons stems at least partly from a significantly distinct geometrical equilibrium compared to the neutral stack, as well as a reorganization permitted by the balanced structural flexibility of the nanowires, in which chirality plays a determining role. Furthermore, the persistence of the photopumped population is facilitated by the presence of an energy barrier between the CS state and neutral ground state, especially due to the absence of hole and electron orbital overlap. Charge recombination, much like charge separation, necessitates electron transfer through intermediary vibronic states, akin to cascade processes in biological photosynthetic systems.

By combining favorable electronic and vibrational characteristics, the studied donor-acceptor system not only achieves effective charge separation but also extends the usable lifespan of the radicals generated. These findings thus pave the way to design systems that decouple charge separation efficiency from immediate radical reactivity, offering new potential for advanced energy and electronic devices.