2023 New's Items

Light-driven electron transfer by Quantum vibronic ratcheting

Roy PP
Widel Z
Therien MJ
Fleming GR
2023

The optical control of coherence to improve and create a new molecular function is a grand challenge in science. In this work, we present a synthetic strategy to build a donor-donor-acceptor (D1D2A) supramolecular construct and tailor vibronic coherence to leverage an efficient long-range electron-transfer by defeating the thermodynamic energy trap imposed by Boltzmann statistics. The relaxed D1* lies 0.35 eV below the D2* state. By a combined transient IR and two-dimensional...

Single-photon absorption and emission from a natural photosynthetic complex

Li Q
Orcutt K
Whaley KB
Fleming GR
2023

Photosynthesis is generally assumed to be initiated by a single photon1,2,...

Infrared Signatures of Phycobilins within the Phycocyanin 645 Complex

Roy PP
Leonardo C
Orcutt K
Oberg C
Scholes GD
Fleming GR
2023

Aquatic photosynthetic organisms evolved to use a variety of light frequencies to perform photosynthesis. Phycobiliprotein phycocyanin 645 (PC645) is a light-harvesting complex in cryptophyte algae able to transfer the absorbed green solar light to other antennas with over 99% efficiency. The infrared signatures of the phycobilin pigments embedded in PC645 are difficult to access and could provide useful information to understand the mechanism behind the high efficiency of energy transfer in PC645. We use visible-pump IR-probe and two-dimensional electronic vibrational spectroscopy...

Reactivity, Regioselectivity, and Synthetic Application of 2-Pyrenyl Units in Scholl Reactions

Pun SH
Wen ECH
Xia Z
Chen H
Miao Q
Fischer FR
2023

We herein report the reactivity and regioselectivity of 2-pyrenyl as a coupling unit in Scholl reactions. On the basis of the Scholl reactions of hexaarylbenzene substrates, we have found that pyrenyl units are preferably oxidized over naphthyl and phenyl units under appropriate Scholl reaction conditions, allowing divergent synthesis through a highly controllable intramolecular coupling sequence. We find that the C1 and C3 positions of the 2-pyrenyl unit are the favorable sites for intramolecular coupling while C4 is not reactive to allow further coupling. The reactivity and...

Fermi-Level Engineering of Nitrogen Core-Doped Armchair Graphene Nanoribbons

Wen ECH
Jacobse PH
Crommie MF
Fischer FR
2023

Substitutional heteroatom doping of bottom-up engineered 1D graphene nanoribbons (GNRs) is a versatile tool for realizing low-dimensional functional materials for nanoelectronics and sensing. Previous efforts have largely relied on replacing C–H groups lining the edges of GNRs with trigonal planar N atoms. This type of atomically precise doping, however, only results in a modest realignment of the valence band (VB) and conduction band (CB) energies. Here, we report the design, bottom-up synthesis, and spectroscopic characterization of nitrogen core-doped 5-atom-wide armchair GNRs (N...

Controlled catalyst transfer polymerization in graphene nanoribbon synthesis

Pun SH
Delgado A
Dadich C
Cronin A
Fischer FR
2023

Exercising direct control over the unusual electronic structures arising from quantum confinement effects in graphene nanoribbons (GNRs) - atomically defined quasi one-dimensional (1D) strips of graphene - is intimately linked to geometric boundary conditions imposed by the bonding within the ribbon. Besides composition and position of substitutional dopant atoms, the symmetry of the unit cell, the width, length, and termination of a GNR are integral factors that collectively can give rise to highly tuneable semiconductors, innate metallicity arising from topological zero-mode...

Engineering Robust Metallic Zero-Mode States in Olympicene Graphene Nanoribbons

McCurdy RD
Delgado A
Louie SG
Fischer FR
2023

Metallic graphene nanoribbons (GNRs) represent a critical component in the toolbox of low-dimensional functional materials technolo-gy serving as 1D interconnects capable of both electronic and quantum information transport. The structural constraints imposed by on-surface bottom-up GNR synthesis protocols along with the limited control over orientation and sequence of asymmetric monomer building blocks during the radical step-growth polymerization has plagued the design and assembly of metallic GNRs. Here we report the regioregular synthesis of GNRs hosting robust metallic states by...

High-Order Fractal Quantum Oscillations in Graphene/BN Superlattices in the Extreme Doping Limit

Shi W
Kahn S
Zettl A
Crommie M
2023

Recent studies of van der Waals (vdW) heterostructures and superlattices have shown intriguing quantum phenomena, but these have been largely explored only in the moderate carrier density regime. Here, we report the probe of high-temperature fractal Brown-Zak (BZ) quantum oscillations through magnetotransport in the extreme doping regimes by applying a newly developed electron beam doping technique. This technique gives access to both ultrahigh electron and hole densities beyond the dielectric breakdown limit in graphene/BN superlattices, enabling the observation of nonmonotonic...

Imaging Field-Driven Melting of a Molecular Solid at the Atomic Scale

Liou F
Tsai HZ
Lischner J
Crommie MF
2023

Solid–liquid phase transitions are basic physical processes, but atomically resolved microscopy has yet to capture their full dynamics. A new technique is developed for controlling the melting and freezing of self-assembled molecular structures on a graphene field-effect transistor (FET) that allows phase-transition behavior to be imaged using atomically resolved scanning tunneling microscopy. This is achieved by applying electric fields to 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane-decorated FETs to induce reversible transitions between molecular solid and liquid phases at...

Local spectroscopy of a gate-switchable moiré quantum anomalous Hall insulator

Zhang C
Zhu T
Zaletel MP
Crommie MF
2023

In recent years, correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have all been observed in several moiré heterostructures. However, understanding of the physical mechanisms behind these phenomena is hampered by the lack of local electronic structure data. Here, we use scanning tunnelling microscopy and spectroscopy to demonstrate how the interplay between correlation, topology, and local atomic structure determines the behaviour of electron-doped twisted monolayer–bilayer graphene. Through gate- and magnetic field-dependent...