2022 New's Items

Self-assembly of nanocrystals into strongly electronically coupled all-inorganic supercrystals

Coropceanu I
Janke EM
Ginsberg NS
Talapin DV
2022

Colloidal nanocrystals of metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline and quasicrystalline phases, but insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. We reversibly self-assembled colloidal nanocrystals of gold, platinum, nickel, lead sulfide, and lead selenide with conductive inorganic ligands into supercrystals exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. The...

Xanthophyll-cycle based model of the rapid photoprotection of Nannochloropsis in response to regular and irregular light/dark sequences

Short AH
Fay TP
Crisanto T
Limmer DT
Fleming GR
2022

We explore the photoprotection dynamics of Nannochloropsis oceanica using time-correlated single photon counting under regular and irregular actinic light sequences. The varying light sequences mimic natural conditions, allowing us to probe the real-time response of non-photochemical quenching (NPQ) pathways. Durations of fluctuating light exposure during a fixed total experimental time and prior light exposure of the algae are both found to have a profound effect on NPQ. These observations are rationalized with a quantitative model based on the xanthophyll cycle and the...

Concerted Electron-Nuclear Motion in Proton-Coupled Electron Transfer-Driven Grotthuss-Type Proton Translocation

Arsenault EA
Guerra WD
Moore TA
Fleming GR
2022

Photoinduced proton-coupled electron transfer and long-range two-proton transport via a Grotthuss-type mechanism are investigated in a biomimetic construct. The ultrafast, nonequilibrium dynamics are assessed via two-dimensional electronic vibrational spectroscopy, in concert with electrochemical and computational techniques. A low-frequency mode is identified experimentally and found to promote double proton and electron transfer, supported by recent theoretical simulations of a similar but abbreviated (non-photoactive) system. Excitation frequency peak evolution and center line...

The initial charge separation step in oxygenic photosynthesis

Yoneda Y
Arsenault EA
Yang S-J
Orcutt K
Iwai M
Fleming GR
2022

Photosystem II is crucial for life on Earth as it provides oxygen as a result of photoinduced electron transfer and water splitting reactions. The excited state dynamics of the photosystem II-reaction center (PSII-RC) has been a matter of vivid debate because the absorption spectra of the embedded chromophores significantly overlap and hence it is extremely difficult to distinguish transients. Here, we report the two-dimensional electronic-vibrational spectroscopic study of the PSII-RC. The simultaneous resolution along both the visible excitation and infrared detection axis is...

Halide perovskites enable polaritonic XY spin Hamiltonian at room temperature

Tao R
Peng K
Haeberlé L
Li Q
Jin D
Fleming GR
Kéna-Cohen S
Zhang X
Bao W
2022

Exciton polaritons, the part-light and part-matter quasiparticles in semiconductor optical cavities, are promising for exploring Bose–Einstein condensation, non-equilibrium many-body physics and analogue simulation at elevated temperatures. However, a room-temperature polaritonic platform on par with the GaAs quantum wells grown by molecular beam epitaxy at low temperatures remains elusive. The operation of such a platform calls for long-lifetime, strongly interacting excitons in a stringent material system with large yet nanoscale-thin geometry and homogeneous properties. Here, we...

Interference between Franck–Condon and Herzberg–Teller Terms in the Condensed-Phase Molecular Spectra of Metal-Based Tetrapyrrole Derivatives

Roy PP
Kundu S
Makri N
Fleming GR
2022

The commonly used Franck–Condon (FC) approximation is inadequate for explaining the electronic spectra of compounds that possess vibrations with substantial Herzberg–Teller (HT) couplings. Metal-based tetrapyrrole derivatives, which are ubiquitous natural pigments, often exhibit prominent HT activity. In this paper, we compare the condensed phase spectra of zinc–tetraphenylporphyrin (ZnTPP) and zinc–phthalocyanine (ZnPc), which exhibit vastly different spectral features in spite of sharing a common tetrapyrrole backbone. The absorption and emission spectra of ZnTPP are characterized...

Synthetic Control of Exciton Dynamics in Bioinspired Cofacial Porphyrin Dimers

Roy PP
Kundu S
Valdiviezo J
Bullard G
Fletcher JT
Liu R
Yang SJ
Zhang P
Beratan DN
Therien MJ
Makri N
Fleming GR
2022

Understanding how the complex interplay among excitonic interactions, vibronic couplings, and reorganization energy determines coherence-enabled transport mechanisms is a grand challenge with both foundational implications and potential payoffs for energy science. We use a combined experimental and theoretical approach to show how a modest change in structure may be used to modify the exciton delocalization, tune electronic and vibrational coherences, and alter the mechanism of exciton transfer in covalently linked cofacial Zn-porphyrin dimers (meso-beta linked AB...

Franck–Condon and Herzberg–Teller Signatures in Molecular Absorption and Emission Spectra

Kundu S
Roy PP
Fleming GR
Makri N
2022

Some molecules of chemical and biological significance possess vibrations with significant Herzberg–Teller (HT) couplings, which render the Franck–Condon (FC) approximation inadequate and cause the breakdown of the well-known mirror-image symmetry between linear absorption and emission spectra. Using a model two-state system with displaced harmonic potential surfaces, we show analytically that the FC-HT interference gives rise to asymmetric intensity modification, which has the same sign for all transitions on one side of the 0–0 absorption line and the opposite sign in the...

Interplay between LHCSR proteins and state transitions governs the NPQ response in Chlamydomonas during light fluctuations

Steen CJ
Burlacot A
Short AH
Niyogi KK
Fleming GR
2022

Photosynthetic organisms use sunlight as the primary energy source to fix CO2. However, in nature, light energy is highly variable, reaching levels of saturation for periods ranging from milliseconds to hours. In the green microalga Chlamydomonas reinhardtii, safe dissipation of excess light energy by nonphotochemical quenching (NPQ) is mediated by light-harvesting complex stress-related (LHCSR) proteins and redistribution of light-harvesting antennae between the photosystems (state transition). Although each component underlying NPQ has been...

Evidence for a Spinon Kondo Effect in Cobalt Atoms on Single-Layer 1T-TaSe2

Chen, Y.
He, W.-Y.
Ruan, W.…..
Mo, S.-K.
Lee, P. A.
Crommie, M. F.
2022

Quantum spin liquids are highly entangled, disordered magnetic states that are expected to arise in frustrated Mott insulators and to exhibit exotic fractional excitations such as spinons and chargons. Despite being electrical insulators, some quantum spin liquids are predicted to exhibit gapless itinerant spinons that yield metallic behaviour in the charge-neutral spin channel. We deposited isolated magnetic atoms onto single-layer 1T-TaSe2, a candidate gapless spin liquid, to probe how itinerant spinons couple to impurity spin centres. Using scanning tunnelling spectroscopy, we...