Winiger et al. (2014) reported that supramolecular polymers self-assembled in water from amphiphilic phenanthrene oligomers, statistically doped with pyrene acceptors, collect and deliver electronic excitation over distances well beyond 100 nm with high fluorescence quantum yields — far beyond the few-nanometer reach of classical Förster resonance energy transfer — and left the mechanism (quantum-coherent excitonic delocalization, incoherent hopping, or an interpolating regime) unresolved, along with the validity of the simplified intrachain statistical-doping estimate of the transfer distance (DET≈150D_{\mathrm{ET}}\approx 150 nm) and the chromophore-level packing of the polymer. In 2025, the same group, with ultrafast spectroscopists, established by femtosecond transient absorption spectroscopy and TD-DFT calculations on DNA-duplex-embedded phenanthrene stacks with pyrene acceptors that transfer in those scaffolds is fully quantum coherent and anti-Kasha in nature, proceeding through high-lying delocalized excited states with exciplex-assisted trapping and a secondary FRET channel. The corresponding mechanistic and quantitative account is still missing for the actual self-assembled, statistically doped, structurally disordered polymer: direct determination of the operating mechanism and the electronic states involved, chromophore-level structural characterization (stacking registry, couplings, bundling), and validation or revision of the transfer-distance estimate and its assumptions. No coherence-sensitive, time-resolved study of the polymer itself is known to date.

Background

Supramolecular polymers are chain-like assemblies held together by reversible non-covalent interactions rather than covalent bonds. Here the building blocks are short amphiphilic oligomers in which three phenanthrene chromophores — flat, three-ring aromatic molecules — are connected by phosphodiester linkages; in water these oligomers stack face-to-face (an H-aggregate-type arrangement, in which face-to-face coupling of the transition dipoles makes the lowest exciton state optically weak) into micrometer-long nanofibers. Phenanthrene acts as the light-absorbing donor, and a small fraction of pyrene chromophores, incorporated statistically during assembly, act as acceptors that trap the collected energy and re-emit it as fluorescence. In artificial and natural light-harvesting systems, excitation energy usually migrates by Förster resonance energy transfer (FRET): incoherent, point-dipole hopping between localized molecular excited states, with a rate falling off as the inverse sixth power of the donor–acceptor separation and an effective reach of only a few nanometers. The alternative is quantum-coherent exciton transfer, in which electronic coupling between closely stacked chromophores delocalizes the excitation over several molecules (an exciton), allowing energy redistribution on femtosecond timescales without stepwise hopping. Winiger, Li, Kumar, Langenegger and Häner (Angew. Chem. Int. Ed. 2014, 53, 13609) reported that pyrene-doped phenanthrene supramolecular polymers transfer electronic excitation over distances well beyond 100 nm — roughly fifty times a typical FRET radius — with high efficiency, which the abstract said 'suggests a quantum coherent process' without claiming it. The transfer distance was estimated with a simplified intrachain, statistical-doping model that assumes strictly intrachain transfer, a random acceptor distribution, particular interchromophore spacings and orientation factors, and negligible interchain transfer and nonradiative losses; these assumptions were not independently validated. The polymer assembly also shows pronounced hysteresis (about 10 °C) between cooling and heating, indicating incompletely characterized assembly thermodynamics, kinetics, and molecular packing (stacking registry, electronic coupling magnitudes, possible bundling of chains). For reviews of exciton transport in molecular aggregates see Brixner, Hildner, Köhler, Lambert and Würthner (Adv. Energy Mater. 2017). Related giant-antenna behavior in dye-loaded polymer nanoparticles (Trofymchuk et al., Nat. Photonics 2017) shows that very high donor-to-acceptor ratios with ultrafast excitation-energy diffusion can also arise in purely soft-matter systems. A decisive step for the same chromophore family came in 2025: Haghighi Pashaki et al. (Angew. Chem. Int. Ed. 2025, 64, e202513001) showed, by femtosecond transient absorption spectroscopy and time-dependent density functional theory (TD-DFT) calculations, that phenanthrene stacks embedded in a DNA duplex transfer energy to a pyrene acceptor by a fully coherent mechanism that breaks Kasha's rule — the empirical rule that emission and photochemistry proceed from the lowest excited state of a given spin multiplicity; here the mediating states are higher-lying, optically bright excited states delocalized over the stack (an 'anti-Kasha' process). Trapping is assisted by an exciplex, a charge-transfer-like excited complex formed between the acceptor and the adjacent donor, while the residual population that relaxes to localized low-lying states is transferred more slowly by ordinary FRET. Adjacent supramolecular systems demonstrate that the incoherent alternative is physically real as well: in oligothiophene nanofibres, long-range room-temperature transport proceeds by incoherent hopping of delocalized excitons (Haedler et al., Nature 2015; Wittmann et al., JACS 2020), and in anthracene supramolecular nanofibers FRET-type hopping with two-to-three-monomer delocalization reaches diffusion lengths up to 350 nm (Pathoor et al., Nano Lett. 2026). What remains untested is the original system itself: whether the coherent anti-Kasha mechanism established in structurally defined DNA-scaffolded stacks operates in the statistically doped, disordered, self-assembled polymer, and what the true transfer-distance limit of that polymer is.

Problem Statement

Give a complete mechanistic and quantitative account of the long-distance, high-efficiency electronic energy transfer in pyrene-doped supramolecular phenanthrene polymers — nanofibers self-assembled in water from amphiphilic phenanthrene oligomers with statistically incorporated pyrene acceptors — as left open by the 2014 report. Concretely, determine: (1) the mechanism by which excitation collected by the phenanthrene stacks reaches the pyrene acceptors over distances exceeding 100 nm — quantum-coherent excitonic delocalization of the kind demonstrated in 2025 for DNA-guided phenanthrene stacks (including its anti-Kasha high-lying delocalized states and exciplex-mediated trapping), classical incoherent Förster-type hopping, or an interpolating regime — together with the electronic states, time scales, and coupling magnitudes involved; (2) the chromophore-level structure of the polymer that sustains or excludes each mechanism — stacking registry, electronic couplings, and possible chain bundling, including how the hysteretic assembly pathway affects them; and (3) on that basis, a validated or revised value and uncertainty for the intrachain statistical-doping estimate DET≈150D_{\mathrm{ET}}\approx 150 nm, in particular its assumptions of strictly intrachain transfer, random acceptor distribution, fixed interchromophore spacing and geometry factors, and negligible interchain transfer and nonradiative losses. These three strands jointly serve one objective — a physically grounded, experimentally tested explanation of the 2014 observation — with the mechanism established for the polymer itself and not transferred untested from the DNA-scaffolded analogue.

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