A Real-Space View of Artificial Light Harvesting
Real-space photoluminescence images distinguish dark and bright states while revealing dipole rotation in strongly coupled molecular rings.
A tip-enhanced photoluminescence experiment has captured the excitonic landscape of artificial cyclic light-harvesting architectures in real space, resolving both bright and dark states beyond the reach of far-field measurements.
The research focused on cyclic zinc phthalocyanine assemblies constructed molecule by molecule with scanning tunneling microscopy. Using tip-enhanced photoluminescence, the team followed how the spectra changed as intermolecular spacing was tuned from weak to intermediate to strong coupling. At large separations, the tetramers behaved much like isolated molecules. As the units were brought closer together, the spectra evolved into split, multi-peak structures consistent with the formation of collective excitonic states.
The near-field measurements also provided a real-space view of those states. In the strongly coupled tetramers, the authors assigned six excitonic states and used the corresponding photoluminescence images to distinguish bright from dark configurations, including states obscured in far-field measurements by diffraction limits and dipole selection rules.
The spatial patterns pointed to a further effect. The transition dipoles of the zinc phthalocyanine units did not remain fixed along the molecular axes, but rotated as coupling developed. The authors traced that behavior to mixing between the molecules’ two orthogonal, degenerate transition dipoles, which together support coherent intermolecular coupling.
The team then compared hollow and solid cyclic architectures. In the hollow ring, the lowest-lying excitonic state was dark, whereas the corresponding state in the solid structure was bright. This structural difference may help explain why hollow cyclic architectures are favored in light-harvesting systems, where suppressing radiative loss can help preserve excitation energy.
The Hidden Collapse of Collagen Order
Chiroptical spectroscopy detects loss of supramolecular collagen order before conventional imaging registers obvious structural damage in aging skin.
A multimodal spectroscopy and imaging workflow has revealed a decoupling between collagen mass and collagen organization in aging skin, with chiroptical spectroscopy detecting loss of hidden structural order before visible matrix damage appears.
Collagen is usually assessed through its visible fiber network, where breakdown shows up as thinning, disorganization, or loss of coverage. In the new study, the Hiroshima-led team instead looked earlier in the hierarchy, asking whether collagen’s internal structural order changes before those larger morphological failures become apparent.
To do so, the researchers combined optical imaging with chiroptical measurements, including synchrotron radiation vacuum-ultraviolet circular dichroism and multidimensional quantum cascade laser vibrational circular dichroism. The spectroscopic measurements tracked supramolecular chirality in the same tissue sections used for imaging, linking visible architecture to structural handedness rather than treating them as separate readouts.
The measurements showed a clear decoupling between collagen mass and collagen organization. Tissue samples could retain their overall collagen content and visible coverage even after their underlying supramolecular chirality had substantially degraded. The hidden internal order of the matrix began to collapse before conventional imaging registered obvious structural damage.
“One way to think about our findings is that conventional imaging methods can show the ‘bricks’ of a collagen structure, but they may miss subtle changes in how those bricks are arranged,” said Ali Haider, first author of the study, in a Hiroshima University press release.
The authors suggest that combining morphology with chiroptical spectroscopy could offer an earlier way to assess tissue integrity, before collagen remodeling becomes obvious at the macroscopic fiber level.
Single-Shot Spectroscopy, Reconfigured
A programmable time-stretch system makes the usual single-shot trade-off between bandwidth, resolution, and speed adjustable between measurements.
Single-shot spectroscopy is useful when transient events cannot be reconstructed from repeated scans. But it usually comes with a trade-off: improving spectral resolution tends to narrow bandwidth or slow acquisition. A reconfigurable time-stretch system now makes that trade-off adjustable between measurements, reaching a reported 86 femtometer resolution in the 1.5 µm band.
The setup combines a pulse picker, a programmable dispersive fiber loop, and a tunable optical filter. In time-stretch spectroscopy, dispersion converts wavelength into arrival time, so more dispersion improves resolution but also broadens the pulse and increases the risk of overlap with the next shot. Here, the authors use switchable dispersion and loop circulation to move between faster, broader, or finer-resolution operating modes.
That flexibility showed up in the test measurements. At low dispersion, the system resolved the periodic structure of a comb filter but not the detailed profile of each absorption line. Increasing the dispersion sharpened the readout from 256 pm to 25.6 pm and then to 6.2 pm, bringing the spectra into close agreement with the reference measurement.
In its highest-resolution mode, the instrument reached 86 fm, or about 10 MHz, using a total dispersion of -145.76 ns/nm over a 1.6 nm bandwidth. The group then applied it to a phase-shifted fiber Bragg grating under strain, tracking wavelength shifts as small as 238.8 fm, following 9 kHz oscillations, and capturing a damped response after a perturbation lasting less than 100 µs.
The study does not remove the usual bandwidth–resolution–speed constraint. But it does make that compromise programmable, giving single-shot spectroscopy a more adaptable way to follow rapidly changing spectral signals.
Operando X-Rays Under Real Catalytic Conditions
Designed for the OÆSE endstation at BESSY II, the operando cell supports gas-solid catalyst studies at up to 20 bar and 400 °C.
A new operando X-ray spectroscopy cell extends soft and hard X-ray absorption measurements into pressure and temperature ranges more relevant to industrial thermocatalysis, addressing a longstanding practical limitation in catalyst studies at synchrotrons.
The sample environment was developed for the OÆSE endstation at BESSY II and is designed to follow gas–solid catalytic reactions at up to 20 bar and 400 °C. This is especially relevant for soft X-ray absorption spectroscopy, which can probe the chemical and electronic states of elements such as carbon, nitrogen, oxygen, and transition metals, but is strongly attenuated by dense gases and solid materials under realistic reaction conditions.
The team demonstrated the cell’s use by following the redox behavior of a cobalt–manganese thin film. That proof-of-principle measurement showed that the setup could track chemical-state changes under the elevated pressures and temperatures that have usually restricted soft X-ray studies. The setup supports measurements across both the soft and the tender/hard X-ray ranges within the same operando framework, bringing surface-sensitive and more bulk-penetrating measurements closer to the conditions used in industrial catalysis.
“This development is a significant milestone, particularly for soft X-rays, as soft X-rays are significantly more attenuated in solids and highly pressurized gases than tender/hard X-rays,” says Catalina Jimenez, co-author of the study, in a recent press release.
The authors suggest that the cell could support studies of thermocatalytic reactions such as Fischer–Tropsch synthesis under conditions closer to those used in practice, where pressure and temperature shape the chemical states being measured.
The Spectacular and Strange
“A Cosmic Weather Report from 4 Billion Years Ago”
The earliest chapters of impact history have mostly been torn up and recycled on Earth. On Mars, however, some of them may still be sitting in the rocks.
After climbing the western rim of Jezero Crater, NASA’s Perseverance rover examined a 75-meter-thick stack of ancient layered rocks known as the Broom Point member. The sequence is likely more than 3.9 billion years old, placing it among the oldest terrain ever explored by a Mars rover. Using rover imaging and multispectral observations, the team identified six distinct rock types, including breccias packed with angular fragments and layers of fine-grained pulverized rock.
The most telling clue came from tiny dark, glassy beads scattered through the layers. Similar spherules can form during volcanism, but their abundance, shapes, and distribution were more consistent with droplets of molten rock thrown out by asteroid impacts. “The different rock layers are a record of variable-sized impacts occurring at different distances from where this rock sequence was accumulating,” said Alex Jones, lead author of the study, in NASA’s press release. “Some large impacts took place very far away, some small impacts nearby. Their debris all ended up landing here, constructing this thick section of rock.”
Some layers are tilted by more than 80 degrees, far too steep to be explained by the Jezero impact alone. The team suggests they may record a cosmic one-two punch: first the much larger Isidis impact tilted the older rocks, then the later Jezero impact fractured and uplifted them.
Perseverance has collected two core samples from the sequence, Bell Island and Main River, which could help date this ancient bombardment if returned to Earth. “If we can pin down the ages of these layers, it would be like reading a cosmic weather report from 4 billion years ago,” said Jones.
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