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Achieving ultranarrow absorption linewidths in the condensed phase enables optical state preparation of specific non-thermal states, a prerequisite for quantum-enabled technologies.

 

The energetic disorder induced by fluctuating liquid environments acts in opposition to the precise control required for coherence-based sensing. Overcoming fluctuations requires a protected quantum subspace that only weakly interacts with the local environment. We report a ytterbium complex that exhibited an ultranarrow absorption linewidth in solution at room temperature with a full width at half maximum of 0.625 milli–electron volts. Using spectral hole burning, we measured an even narrower linewidth of 410 pico–electron volts at 77 kelvin. Narrow linewidths allowed low-field magnetic circular dichroism at room temperature, used to sense Earth-scale magnetic fields. These results demonstrated that ligand protection in lanthanide complexes could substantially diminish electronic state fluctuations. We have termed this system an “atomlike molecular sensor” (ALMS) and proposed approaches to improve its performance.

 

Near infrared (NIR, 700–1000 nm) and short-wave infrared (SWIR, 1000–2000 nm) dye molecules exhibit significant nonradiative decay rates from the first singlet excited state to the ground state. While these trends can be empirically explained by a simple energy gap law, detailed mechanisms of nearly universal behavior have remained unsettled for many cases. Theoretical and experimental results for two representative NIR/SWIR dye molecules reported here clarify the key mechanism for the observed energy gap law behavior. It is shown that the first derivative nonadiabatic coupling terms serve as major coupling pathways for nonadiabatic decay processes from the first excited singlet state to the ground state for these NIR and SWIR dye molecules and that vibrational modes other than the highest frequency modes also make significant contributions to the rate. This assessment is corroborated by further theoretical comparison with possible alternative mechanisms of intersystem crossing to triplet states and also by comparison with experimental data for deuterated molecules. 

Cryo-electron microscopy has delivered a resolution revolution for biological self-assemblies, yet only a handful of structures have been solved for synthetic supramolecular materials. Particularly for chromophore supramolecular aggregates, high-resolution structures are necessary for understanding and modulating the long-range excitonic coupling. Here, we present a 3.3 Å structure of prototypical biomimetic light-harvesting nanotubes derived from an amphiphilic cyanine dye (C8S3-Cl). Helical 3D reconstruction directly visualizes the chromophore packing that controls the excitonic properties. Our structure clearly shows a brick layer arrangement, revising the previously hypothesized herringbone arrangement. Furthermore, we identify a new non-biological supramolecular motif—interlocking sulfonates—that may be responsible for the slip-stacked packing and J-aggregate nature of the light-harvesting nanotubes. This work shows how independently obtained native-state structures complement photophysical measurements and will enable accurate understanding of (excitonic) structure–function properties, informing materials design for light-harvesting chromophore aggregates. 

We demonstrate that deuteration is a generally applicable strategy that leads to enhanced quantum yields of fluorescence, longer-lived singlet excited states and suppressed rates of non-radiative deactivation processes.

 

Quantitative fluorescence quenching is a common analytical approach to studying the mechanism of chemical reactions. The Stern–Volmer (S–V) equation is the most common expression used to analyze the quenching behavior and can be used to extract kinetics in complex environments. However, the approximations underlying the S–V equation are incompatible with Förster Resonance Energy Transfer (FRET) acting as the primary quenching mechanism. The nonlinear distance dependence of FRET leads to significant departures from “standard” S–V quenching curves, both by modulating the interaction range of donor species and by increasing the effect of component diffusion. We demonstrate this inadequacy by probing the fluorescence quenching of long-lifetime lead sulfide quantum dots mixed with plasmonic covellite copper sulfide nanodisks (NDs), which serve as perfect fluorescent quenchers. By applying kinetic Monte Carlo methods, which consider particle distributions and diffusion, we are able to quantitatively reproduce experimental data, which show significant quenching at very small concentrations of NDs. The distribution of interparticle distances and diffusion are concluded to play important roles in fluorescence quenching, particularly in the shortwave infrared, where photoluminescent lifetimes are often long relative to diffusion time scales.

 

Large area absorbers with localized defect emission are of interest for energy concentration via the antenna effect. Transfer between 2D and 0D quantum-confined structures is advantageous as it affords maximal lateral area antennas with continuously tunable emission. We report the quantum efficiency of energy transfer in in situ grown HgTe nanoplatelet (NPL)/quantum dot (QD) heterostructures to be near unity (>85%), while energy transfer in separately synthesized and well separated solutions of HgTe NPLs to QDs only reaches 47 ± 11% at considerably higher QD concentrations. Using Kinetic Monte Carlo simulations, we estimate an exciton diffusion constant of 1–10 cm2/s in HgTe NPLs, the same magnitude as that of 2D semiconductors. We also simulate in-solution energy transfer between NPLs and QDs, recovering an R–4 dependence consistent with 2D-0D near-field energy transfer even in randomly distributed NPL/QD mixtures. This highlights the advantage of NPLs 2D morphology and the efficiency of NPL/QD heterostructures and mixtures for energy harvesting.