Building on earlier studies of PCET and PCEnT, a team led by Prof. Kaifeng Wu at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences investigated another important but poorly understood process: triplet energy transfer linked to proton movement.

Triplet energy transfer is a major pathway for moving energy in both natural and synthetic systems, but it operates differently from singlet energy transfer. Understanding how proton motion influences this process could open new ways to control energy flow in advanced materials.

In a study published in Nature Materials, the researchers reported a previously unknown mechanism called proton shuttle-assisted triplet energy transfer (PS-TET). The process was observed as energy moved from ZnSe-based colloidal quantum dots (QDs) to phenol-pyridine dyadic acceptors attached to their surfaces.

How the Proton Shuttle Moves Energy

When the ZnSe QDs absorb light, they enter an excited state. A hole then moves from ZnSe to phenol while a proton simultaneously shifts from phenol to pyridine.

Next, an electron transfers from ZnSe to the phenoxyl radical. At the same time, the proton moves back from pyridinium to its original location. Together, these linked steps produce the overall movement of spin-triplet energy from the ZnSe QDs to the phenol-pyridine dyads.

The proton ultimately ends up where it started, but its temporary movement has a major effect. The shuttle greatly increases both the speed and efficiency of triplet energy transfer compared with a methylated analog that does not contain the proton shuttle.

The team also found that adding a strongly electron-withdrawing trifluoromethyl substituent to pyridine can change the order in which the proton-coupled electron and hole transfer steps occur.

Quantum Tunneling at Room Temperature

The rate of PS-TET changed very little with temperature. This suggests that the proton does not move through a conventional heat-driven process. Instead, it appears to travel through quantum mechanical tunneling.

Calculations involving proton vibrational wavefunction overlap integrals supported this interpretation. These integrals help determine which excited-state relaxation pathways are favored and steer the system toward efficient triplet energy migration.

The findings show that quantum effects can be used to control charge and energy transfer in complex materials even at room temperature.

Potential Uses in Solar Cells, Lasers, and Catalysis

“The discovery of the PS-TET mechanism has profound implications for many modern molecular technologies involving the spin-triplet excited states of molecules,” Prof. Wu noted.

Increasing triplet generation efficiency could improve photoredox and environmental catalysis. In other technologies, however, triplet formation may need to be limited. Organic optoelectronic devices such as solar cells and lasers can perform better when unwanted triplet states are suppressed.

The study suggests that scientists may be able to tune triplet formation as needed. Creating a proton shuttle could enhance the process, while removing the shuttle could reduce or prevent it.

MIT researchers have now developed an approach that could lead to smaller, more durable lidar sensors that operate without any moving parts. Their advance centers on a new silicon-photonics chip, a type of semiconductor device that controls light instead of electrical signals.

Existing lidar systems built with silicon-photonics chips usually have a narrow field of view. As a result, they struggle to scan areas located toward the edges of a scene. Previous attempts to expand this viewing range have often introduced extra noise and reduced measurement accuracy.

The MIT team addressed those problems by creating an array of integrated antennas that greatly limits unwanted crosstalk, which occurs when neighboring antennas interfere with one another. The design allows the chip to scan across a broader field of view while producing less noise than other silicon-photonics-based methods.

A Smaller Lidar System With a Wider View

The advance could support the development of more capable lidar sensors for challenging uses, including autonomous vehicle navigation, aerial mapping, and the monitoring of construction sites.

“The functionality we demonstrated in this work solves a fundamental problem for integrated optical-phased-array technology, enabling future lidar sensors that can achieve significantly higher performance than we could demonstrate previously,” says Jelena Notaros, the Robert J. Shillman Career Development Associate Professor of Electrical Engineering and Computer Science (EECS) at MIT, a member of the Research Laboratory of Electronics, and senior author of a paper on this innovation.

The study also includes lead author and EECS graduate student Henry Crawford-Eng, along with EECS graduate students Andres Garcia Coleto, Benjamin M. Mazur, Daniel M. DeSantis, and Tal Sneh. The findings were published recently in Nature Communications.

How Lidar Maps Its Surroundings

Many traditional lidar systems use a large rotating unit to direct light pulses across a scene. When the light strikes nearby objects, it reflects back toward the sensor. The returning signals provide the information needed to reconstruct a detailed map of the environment.

Silicon-photonics-based lidar works differently. Rather than rotating a mechanical device, it scans a beam of light electronically in several directions with a system known as an integrated optical phased array (OPA).

At the heart of an OPA is a group of integrated antennas. Each antenna contains tiny, regularly spaced variations along its length. These features, known as corrugations, cause light from an input source to scatter upward and out of the photonic chip.

Researchers can control the direction of the outgoing beam by changing the phase of the light sent to each antenna. Adjusting these phases changes the angle at which the array releases light, making it possible to steer the beam without moving any physical components.

The Antenna Spacing Problem

Placing the antennas close together creates a serious obstacle. Neighboring antennas can couple with one another, scrambling the light they produce. Engineers have traditionally prevented this interference by increasing the distance between antennas, but wider spacing creates a different set of problems.

When antennas are too far apart, the array produces several copies of the same beam at different angles. The primary beam can only be moved a limited distance before it becomes difficult to distinguish from these additional copies.

“This limits our field of view, so the autonomous vehicle now only knows what is in front of it for a certain angular range,” Garcia Coleto explains.

The unwanted beam copies, called grating lobes, can confuse the sensor and generate false detections. They also consume energy that could otherwise be directed into the main beam.

To overcome this tradeoff, the MIT researchers developed antennas with reduced crosstalk that can be positioned close together without strongly coupling.

Three Antenna Shapes Reduce Interference

In a conventional OPA, every antenna has an identical structure and uses the same pattern of corrugations. When these matching antennas are placed close together, they interact very strongly.

The MIT team instead created a repeating set of three antennas with distinct shapes. They changed the width of the antennas as well as the size and placement of the corrugations. Because the antennas have different geometries, each one also has a different propagation coefficient, which describes how light moves through the structure.

“Because the antennas have very different propagation coefficients, when we put them close together, essentially each antenna doesn’t ‘see’ the antenna next to it. Therefore, it won’t couple with its neighbor,” Garcia Coleto says.

Making Different Antennas Behave the Same Way

Reducing the coupling was only part of the challenge. Although the antennas needed different propagation coefficients, they still had to release light in the same consistent manner.

The team designed the antennas around three essential requirements.

Each antenna had to emit the same amount of light. Every antenna also needed to release its beam at the same angle when receiving the same wavelength. Finally, the angle of emission had to change evenly across the entire array as the beam was steered.

“We have this challenge where we require the antennas to have different geometries to reduce the crosstalk, but we need to simultaneously design the antennas to have the same emission characteristics. While it is possible to engineer this, it is extremely difficult because, typically, when antennas are designed with different geometries, they tend to behave differently,” Crawford-Eng says.

The researchers began by developing the basic electromagnetic theory describing how radiative modes couple. They then used this theoretical framework to guide the design and computer simulation of the antennas.

Based on those calculations, the team manufactured an OPA containing the reduced-crosstalk antennas. The antennas were placed much closer together than those in a conventional system, and the completed device was then tested experimentally.

Interference Falls From About 100 Percent to 1 Percent

Under the conditions of the experiment, a typical OPA would have produced coupling of approximately 100 percent. The MIT design lowered that coupling to about 1 percent while still generating one clean and precise beam.

The system accurately steered the beam across a broad field of view without producing any grating lobes. This combination of wide scanning, low interference, and strong beam quality addresses one of the central obstacles facing integrated lidar technology.

The researchers now plan to refine the method so the system can cover an even broader viewing range. They are also studying another possible approach to wide field-of-view performance that emerged while they were developing the underlying theory.

“This work addresses a longstanding challenge in integrated optical phased arrays: simultaneously achieving both a wide field of view, which requires dense antenna spacing, and high beam quality, which requires low crosstalk between neighboring antennas. The authors solve this problem with an elegant antenna design. Their innovation is an important step forward for chip-scale, solid-state beam-steering technology,” says Joyce Poon, professor of electrical and computer engineering at the University of Toronto and director of the Max Planck Institute of Microstructure Physics, who was not involved with this work.

The Semiconductor Research Corporation, the National Science Foundation, an MIT MathWorks Fellowship, the U.S. Department of War, and the MIT Rolf G. Locher Endowed Fellowship supported the research, in part.

Some of the work was carried out using MIT.nano facilities.

Researchers worldwide are searching for ways to stay ahead of these rapidly changing microbes. One promising strategy is not to invent a completely new antibiotic, but to help existing drugs work again. This is the idea behind antibiotic adjuvants, which are companion molecules that do not kill bacteria directly but instead restore the power of antibiotics.

Building New Molecules to Speed Drug Discovery

Professor John Moses and his team at Cold Spring Harbor Laboratory (CSHL) have spent years developing chemical reactions that can make the drug discovery process faster and more efficient.

The researchers use a technique called diversity oriented clicking (DOC), which was created in the Moses laboratory. With this method, they have built a library containing more than 150 different compounds. Molecules from this collection have already contributed to research on both antibiotic resistance and cancer.

Now, through a collaboration with Scripps Research, the library has helped scientists restore the effectiveness of vancomycin. This powerful antibiotic is commonly used against severe infections, including those caused by MRSA and Clostridium difficile (C. diff). Both pathogens can develop resistance and become “superbugs” that evade frontline drugs such as vancomycin. They can then spread through hospitals, nursing homes, and communities.

Restoring Vancomycin Against Resistant Bacteria

In the new study, scientists from the Moses laboratory at CSHL worked with Professor Howard Hang’s team at Scripps to identify a way to make vancomycin effective again.

The researchers targeted a bacterial enzyme called secreted antigen A (SagA). They blocked the enzyme using a small molecule known as pghi-4, which was first discovered in the Moses laboratory in 2020.

When drug-resistant E. faecium was treated with both vancomycin and pghi-4, the antibiotic regained its ability to kill the bacteria.

For Moses, one of the most notable parts of the finding is that the research did not begin as a direct search for a new antibiotic.

“This discovery came from fundamental chemical research,” he explains. “Reaction development led to the discovery of the first inhibitor of an important enzyme involved in antibiotic resistance. This is a process we’re constantly refining to both keep our library of molecules up to date and add more for collaborators to take advantage of in their research.”

A Broader Strategy Against Superbugs

By making the molecular library available to other researchers, the team hopes similar approaches could eventually lead to treatments for additional drug-resistant infections. These could include resistant forms of tuberculosis.

“This work reflects a philosophy of chemistry that’s designed to accelerate drug discovery in its purest form,” says Moses. “By using reliable, robust, and intelligent chemical reactions, we can build new molecules more efficiently. That’s exactly the approach we used here.”

As antibiotic resistance grows around the world, the findings show that important medical advances may come from rethinking the chemistry of drugs that already exist. A future treatment may begin not with a new antibiotic, but with a carefully designed molecule that helps an old one work again.

Funding

National Institutes of Health, National Cancer Institute, Australian Research Council, New York State Biodefense Commercialization Fund, F.M. Kirby Foundation, Starr Foundation