2024 New's Items

In Situ X-ray Scattering Reveals Coarsening Rates of Superlattices Self-Assembled from Electrostatically Stabilized Metal Nanocrystals Depend Nonmonotonically on Driving Force

Christian P. N. Tanner
James K. Utterback
Joshua Portner
Igor Coropceanu
Avishek Das
Christopher J. Tassone
Samuel W. Teitelbaum
David T. Limmer
Dmitri V. Talapin
Naomi S. Ginsberg
2024

Self-assembly of colloidal nanocrystals (NCs) into superlattices (SLs) is an appealing strategy to design hierarchically organized materials with promising functionalities. Mechanistic studies are still needed to uncover the design principles for SL self-assembly, but such studies have been difficult to perform due to the fast time and short length scales of NC systems. To address this challenge, we developed an apparatus to directly measure the evolving phases in situ and in real time of an electrostatically stabilized Au NC solution before, during, and after it is...

Entropy as a Design Principle in the Photosystem II Supercomplex

Hall JL
Yang SJ
Limmer DT
Fleming GR
2024
Photosystem II (PSII) can achieve near-unity quantum efficiency of light harvesting in ideal conditions and can dissipate excess light energy as heat to prevent formation of reactive oxygen species under light stress. Understanding how this pigment-protein complex accomplishes these opposing goals is a topic of great interest that has so far been explored primarily through the lens of the system energetics. Despite PSII's known flat energy landscape, a thorough consideration of the entropic effects on energy transfer in PSII is lacking. In this work, we aim to discern the free energetic...

Bidirectional Energy Flow in the Photosystem II Supercomplex

Cristina Leonardo
Shiun-Jr Yang
Kaydren Orcutt
Masakazu Iwai
Eric A. Arsenault
Graham R. Fleming. Phys Chem B
2024

The water-splitting capability of Photosystem II (PSII) of plants and green algae requires the system to balance efficient light harvesting along with effective photoprotection against excitation in excess of the photosynthetic capacity, particularly under the naturally fluctuating sunlight intensity. The comparatively flat energy landscape of the multicomponent structure, inferred from the spectra of the individual pigment–protein complexes and the rather narrow and featureless absorption spectrum, is well known. However, how the combination of the required functions emerges from...

Coherence in Chemistry: Foundations and Frontiers

J.D. Shultz et al. Jonathan D. Schultz
Jonathon L. Yuly
Eric A. Arsenault
Kelsey Parker
Sutirtha N. Chowdhury
Reshmi Dani
Sohang Kundu
Hanggai Nuomin
Zhendian Zhang
Jesuś Valdiviezo
Peng Zhang
Kaydren Orcutt
Seogjoo J. Jang
Graham R. Fleming
Nancy Makri
Jennifer P. Ogilvie
Michael J. Therien
Michael R. Wasielewski
David N. Beratan
2024

Coherence refers to correlations in waves. Because matter has a wave-particle nature, it is unsurprising that coherence has deep connections with the most contemporary issues in chemistry research (e.g., energy harvesting, femtosecond spectroscopy, molecular qubits and more). But what does the word “coherence” really mean in the context of molecules and other quantum systems? We provide a review of key concepts, definitions, and methodologies, surrounding coherence phenomena in chemistry, and we describe how the terms “coherence” and “quantum coherence” refer to many...

Chlorophyll to zeaxanthin energy transfer in nonphotochemical quenching: An exciton annihilation-free transient absorption study

T.Y. Lee
L. Lam, D
Patel-Tupper
P.P. Roy
S.A. Ma
H.Lam, A
Lucas-Demott
N.G. Karavolias
M. Iwai
K.K. Niyogi
G.R. Fleming. PNAS
2024
Zeaxanthin (Zea) is a key component in the energy-dependent, rapidly reversible, nonphotochemical quenching process (qE) that regulates photosynthetic light harvesting. Previous transient absorption (TA) studies suggested that Zea can participate in direct quenching via chlorophyll (Chl) to Zea energy transfer. However, the contamination of intrinsic exciton–exciton annihilation (EEA) makes the assignment of TA signal ambiguous. In this study, we present EEA-free TA data using Nicotiana benthamiana thylakoid membranes, including the wild type and three NPQ mutants (npq1, npq4, and lut2)...

The development and applications of multidimensional biomolecular spectroscopy illustrated by photosynthetic light harvesting

Graham R
Fleming and Gregory D.Scholes
2024

The parallel and synergistic developments of atomic resolution structural information, new spectroscopic methods, their underpinning formalism, and the application of sophisticated theoretical methods have led to a step function change in our understanding of photosynthetic light harvesting, the process by which photosynthetic organisms collect solar energy and supply it to their reaction centers to initiate the chemistry of photosynthesis. The new spectroscopic methods, in particular multidimensional spectroscopies, have enabled a transition from recording rates of processes to focusing...

EPR Spin-Trapping for Monitoring Temporal Dynamics of Singlet Oxygen during Photoprotection in Photosynthesis

Collin J. Steen
Jens Niklas
Oleg G. Poluektov
Lisa M. Utschig
Richard D. Schaller
Graham R. Fleming
2024

A central goal of photoprotective energy dissipation processes is the regulation of singlet oxygen (1O2*) and reactive oxygen species in the photosynthetic apparatus. Despite the involvement of 1O2* in photodamage and cell signaling, few studies directly correlate 1O2* formation to nonphotochemical quenching (NPQ) or lack thereof. Here, we combine spin-trapping electron paramagnetic resonance (EPR) and time-resolved fluorescence spectroscopies to track in real time the involvement of 1O2...

Evidence for excitonic insulator ground state in triangulene Kagome lattice

Delgado A
Dusold C
Jing J
Cronin A
Dadich C
Louie SG
Fischer FR
2023
Electron-hole pair excitations in semiconductors have been predicted to be able to give rise to a highly correlated many-body ground state, the excitonic insulator (EI). Under appropriate conditions below a critical temperature (Tc), strongly bound electron-hole pairs spontaneously form and undergo a phase transition from a normal band insulator into an exciton condensate, transforming the parent material into a novel correlated insulator. Despite recent advances in spectroscopic tools, clear direct experimental evidence for the EI state has been elusive and is often obfuscated by...

Flat band, tunable chiral anomaly, and pitchfork bifurcation in a honeycomb lattice

Saroka VA
Kong F
Bogani L
Downing CA
Payod RB
Fischer FR
Sun X
2024

Chiral anomaly engineering has been established as one of the mechanisms for achieving energy efficient dissipationless transport. Here we show how to design tunable chiral anomalies in a honeycomb lattice free of any magnetic fields. By applying an external electric field to a flat band material with a broken inversion symmetry, we generate electronic modes exhibiting chiral anomalies capable of disorder resilient transport in the bulk of the material. As the electric field increases, the system exhibits an unusual cubic-like dispersion. By providing a performance comparable to other...

Electric-Field-Driven Localization of Molecular Nanowires in Wafer-Scale Nanogap Electrodes

Wong HX
Fischer FR
2024

As integrated circuits continue to scale toward the atomic limit, bottom-up processes, such as epitaxial growth, have come to feature prominently in their fabrication. At the same time, chemistry has developed highly tunable molecular semiconductors that can perform the functions of ultimately scaled circuit components. Hybrid techniques that integrate programmable structures comprising molecular components into devices however are sorely lacking. Here we demonstrate a wafer-scale process that directs the localization of a conductive polymer, Mw = 20 kg mol–1...