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Electronic structure and dynamics determine material properties and behavior. Important time scales for electronic dynamics range from attoseconds to milliseconds. Two-dimensional optical spectroscopy has proven an incisive tool to probe fast spatiotemporal electronic dynamics in complex multichromophoric systems. However, acquiring these spectra requires long point-by-point acquisitions that preclude observations on the millisecond and microsecond time scales. Here we demonstrate that imaging temporally encoded information within a homogeneous sample allows mapping of the evolution of the electronic Hamiltonian with femtosecond temporal resolution in a single-laser-shot, providing real-time maps of electronic coupling. This method, which we call GRadient-Assisted Photon Echo spectroscopy (GRAPE), eliminates phase errors deleterious to Fourier spectroscopies while reducing the acquisition time by orders of magnitude using only conventional optical components. In analogy to MRI in which magnetic field gradients are used to create spatial correlation maps, GRAPE spectroscopy takes advantage of a similar type of spatial encoding to construct electronic correlation maps. Unlike magnetic resonance, however, this spatial encoding of the nonlinear polarization along the excitation frequency axis of the two-dimensional spectrum results in no loss in signal while simultaneously reducing overall noise. Correlating the energy transfer events and electronic coupling occurring in tens of femtoseconds with slow dynamics on the subsecond time scale is fundamentally important in photobiology, solar energy research, nonlinear spectroscopy, and optoelectronic device characterization.

The structure and dynamics of froths have been subjects of intense interest owing to the desire to understand the behaviour of complex systems where topological intricacy prohibits exact evaluation of the ground state. The dynamics of a traditional froth involves drainage and drying at the cell boundaries; thus, it is irreversible. Here, we report a new member of the froth family: suprafroth, in which the cell boundaries are superconducting and the cell interior is normal, or non-superconducting. Despite having a very different microscopic origin, topological analysis of the structure of the suprafroth shows that the same statistical laws, such as those of von Neumann and of Lewis apply to a suprafroth. Furthermore, for the first time in the analysis of froths, there is a global measurable property, the magnetic moment, which can be directly related to the suprafroth structure. We propose that this suprafroth is a model system for the analysis of the complex physics of two-dimensional froths—with magnetic field and temperature as external (reversible) control parameters. Froths and foams are complex structures, particularly those that disappear irreversibly. Superconducting froth, however, can be reversibly controlled by several external parameters, so it may help quantify froth dynamics across different systems.

In carrier multiplication, the absorption of a single photon results in two or more electron–hole pairs. Quantum dots are promising materials for implementing carrier multiplication principles in real-life technologies. So far, however, most of research in this area has focused on optical studies of solution samples with yet to be proven relevance to practical devices. Here we report ultrafast electro-optical studies of device-grade films of electronically coupled quantum dots that allow us to observe multiplication directly in the photocurrent. Our studies help rationalize previous results from both optical spectroscopy and steady-state photocurrent measurements and also provide new insights into effects of electric field and ligand treatments on multiexciton yields. Importantly, we demonstrate that using appropriate chemical treatments of the films, extra charges produced by carrier multiplication can be extracted from the quantum dots before they are lost to Auger recombination and hence can contribute to photocurrent of practical devices. In semiconductors, the absorption of a high energy photon can result in the formation of several charge pairs. Here the authors perform ultrafast photocurrent measurements on thin films to explore how quantum dot couplings and the electric field influence multiexciton photovoltaic devices.

Understanding charge transport and recombination dynamics in photoexcited colloidal quantum dot (QD) solids is key to their applications in optoelectronic devices. Towards this end, we conduct transient photocurrent studies of films of electronically coupled, device-grade PbSe QD films. We observe that the photocurrent amplitude detected following excitation with a short 100 fs pulse is virtually temperature independent down to 6 K, suggesting a tunnelling mechanism of early-time photoconductance. The later-time signal exhibits clear signatures of thermal activation with characteristic energies that are surprisingly robust and independent of the exact type of QD surface treatment. We attribute this behaviour to the involvement of intrinsic fine-structure states and specifically the electron–hole exchange interaction, which creates an energetic barrier to electron–hole separation between adjacent QDs. At room temperature, which is well above the largest activation energy, relaxation of photoconductivity is dominated by non-geminate recombination involving mobile band-edge carriers of one sign and low-mobility carriers of the opposite sign (pre-existing and photoexcited) residing in intragap states. This process leads to memory-less dynamics when the photocurrent relaxation time is directly linked to the instantaneous carrier density. Understanding the recombination dynamics in quantum dots is crucial for their use in optoelectronic devices. A photocurrent spectroscopy study shows how two distinct relaxation mechanisms are at play over different timescales.

Time-resolved ultrafast optical probes of chiral dynamics provide a new window allowing us to explore how interactions with such structured environments drive electronic dynamics. Incorporating optical activity into time-resolved spectroscopies has proven challenging because of the small signal and large achiral background. Here we demonstrate that two-dimensional electronic spectroscopy can be adapted to detect chiral signals and that these signals reveal how excitations delocalize and contract following excitation. We dynamically probe the evolution of chiral electronic structure in the light-harvesting complex 2 of purple bacteria following photoexcitation by creating a chiral two-dimensional mapping. The dynamics of the chiral two-dimensional signal directly reports on changes in the degree of delocalization of the excitonic states following photoexcitation. The mechanism of energy transfer in this system may enhance transfer probability because of the coherent coupling among chromophores while suppressing fluorescence that arises from populating delocalized states. This generally applicable spectroscopy will provide an incisive tool to probe ultrafast transient molecular fluctuations that are obscured in non-chiral experiments. Nonlinear chiral optical activity is difficult to measure because of weak signal amidst strong achiral background. Here, the authors perform a nonlinear chiral two-dimensional spectroscopic mapping of light-harvesting complex 2 during photoexcitation and observe exciton delocalization.

The structure and dynamics of froths have been subjects of intense interest due to the desire to understand the behaviour of complex systems where topological intricacy prohibits exact evaluation of the ground state. The dynamics of a traditional froth involves drainage and drying in the cell boundaries, thus it is irreversible. We report a new member to the froths family: suprafroth, in which the cell boundaries are superconducting and the cell interior is normal phase. Despite very different microscopic origin, topological analysis of the structure of the suprafroth shows that statistical von Neumann and Lewis laws apply. Furthermore, for the first time in the analysis of froths there is a global measurable property, the magnetic moment, which can be directly related to the suprafroth structure. We propose that this suprafroth is a new, model system for the analysis of the complex physics of two-dimensional froths.

Biological invasions provide a unique opportunity to investigate rapid adaptation and evolution as the introduced taxa adapt to biogeographic contexts or habitats in which they have not evolved. The capacity of populations to evolve is generally thought to be constrained by their existing heritable genetic variation, which is usually associated with variation in genomic DNA nucleotide sequences. However, there is increasing acceptance that a range of mechanisms—collectively termed ‘epigenetics’ can alter gene function and affect ecologically important traits. Epigenetic processes may mediate adaptive phenotypic plasticity and provide heritable variation on a finer timescale than DNA sequence-based mutations. This review focuses on DNA methylation, a well-studied epigenetic mechanism known to be associated with biological adaptation to environmental stress. We explore the role of DNA methylation in characterising the adaptive potential of invasive species. We also provide an overview of studies focused on DNA methylation and invasive species to date, and identify knowledge gaps and potential ways to advance understanding of epigenetic-based adaptation. A summary of the literature suggests that DNA methylation could play a key role in the success of invasive species. Introduced populations with reduced genetic diversity often display increased DNA methylation variation in comparison with native populations, which could create phenotypic diversity when it is most required. Recent data show that DNA methylation could contribute to adaptation through both phenotypic plasticity and heritable variation, particularly through clonal reproduction. From a methodological perspective, recent advances in molecular techniques provide an exciting opportunity to explore the functional relevance of DNA methylation to successful biological invasions. Gaining a greater understanding of the adaptive and evolutionary processes that contribute to invasion success is critical for preventing and managing the future introduction, establishment and spread of invasive species.

SARS-CoV-2 infection, and resulting disease, COVID-19, has a high mortality amongst patients with haematological malignancies. Global vaccine rollouts have reduced hospitalisations and deaths, but vaccine efficacy in patients with haematological malignancies is known to be reduced. The UK-strategy offered a third, mRNA-based, vaccine as an extension to the primary course in these patients. The MARCH database is a retrospective observational study of serological responses in patients with blood disorders. Here we present data on 381 patients with haematological malignancies. By comparison with healthy controls, we report suboptimal responses following two primary vaccines, with significantly enhanced responses following the third primary dose. These responses however are heterogeneous and determined by haematological malignancy sub-type and therapy. We identify a group of patients with continued suboptimal vaccine responses who may benefit from additional doses, prophylactic extended half-life neutralising monoclonal therapies (nMAB) or prompt nMAB treatment in the event of SARS-CoV-2 infection. SARS-CoV-2 vaccination has shown reduced efficacy in patients with haematological malignancies. Here, the authors show that a third vaccine is able to enhance SARS-CoV-2 antibody responses in most cases in a cohort of 381 patients with haematological malignancies.