The Zigmantas Group has published a new article in Nature Communications entitled "Ultrafast coherence transfer in DNA-templated silver nanoclusters"
"DNA-templated silver nanoclusters of a few tens of atoms or less have come into prominence over the last several years due to very strong absorption and efficient emission. Applications in microscopy and sensing have already been realized, however little is known about the excited-state structure and dynamics in these clusters. Here we report on a multidimensional spectroscopy investigation of the energy-level structure and the early-time relaxation cascade, which eventually results in the population of an emitting state. We find that the ultrafast intramolecular relaxation is strongly coupled to a specific vibrational mode, resulting in the concerted transfer of population and coherence between excited states on a sub-100 fs timescale."
Swedish Organic Photovoltaics Meeting
Prof. Ivan Scheblykin and Prof. Petter Persson will be hosting a meeting on organic photovoltaics at the Chemistry Centre, Lund University on Thursday May 11 (10.30 - 18.00) and Friday May 12 (9.00-12.00). Visitors from groups in Linköping (Olle Inganäs, Fengling Zhang), Chalmers (Christian Muller, Ergang Wang), and Karlstad (Ellen Moons) will be present.
The talks will cover a broad spectrum of science from fundamental process in organic materials to device properties and their optimization.
Please save the dates if you are interested to participate in this event which, we hope will give us great opportunities for fruitful scientific discussions.
New publication in Nature Plants
The Zigmantas Group in collaboration with Roberto Bassi's group at University of Verona has published a new article in Nature Plants entitled "Two mechanisms for dissipation of excess light in monomeric and trimeric light-harvesting complexes"
"Oxygenic photoautotrophs require mechanisms for rapidly matching the level of chlorophyll excited states from light harvesting with the rate of electron transport from water to carbon dioxide. These photoprotective reactions prevent formation of reactive excited states and photoinhibition. The fastest response to excess illumination is the so-called non-photochemical quenching which, in higher plants, requires the luminal pH sensor PsbS and other yet unidentified components of the photosystem II antenna. Both trimeric light-harvesting complex II (LHCII) and monomeric LHC proteins have been indicated as site(s) of the heat-dissipative reactions. Different mechanisms have been proposed: energy transfer to a lutein quencher in trimers, formation of a zeaxanthin radical cation in monomers. Here, we report on the construction of a mutant lacking all monomeric LHC proteins but retaining LHCII trimers. Its non-photochemical quenching induction rate was substantially slower with respect to the wild type. A carotenoid radical cation signal was detected in the wild type, although it was lost in the mutant. We conclude that non-photochemical quenching is catalysed by two independent mechanisms, with the fastest activated response catalysed within monomeric LHC proteins depending on both zeaxanthin and lutein and on the formation of a radical cation. Trimeric LHCII was responsible for the slowly activated quenching component whereas inclusion in supercomplexes was not required. This latter activity does not depend on lutein nor on charge transfer events, whereas zeaxanthin was essential."
New publication in Nature
A group of researchers led by Pavel Chábera from Chemical Physics has published a new article in Nature entitled "A low-spin Fe(III) complex with 100-ps ligand-to-metal charge transfer photoluminescence"
" Transition-metal complexes are used as photosensitizers1, in light-emitting diodes, for biosensing and in photocatalysis2. A key feature in these applications is excitation from the ground state to a charge-transfer state3, 4; the long charge-transfer-state lifetimes typical for complexes of ruthenium5 and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron6 and copper7 being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs6, 8, 9, 10, it remains a formidable scientific challenge11 to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered12 photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers13, 14, 15. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(III) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes4, 16, 17. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers. "
New publication in Nature Communications
The Yartsev Group has published a new article in Nature Communications entitled "Electron–acoustic phonon coupling in single crystal CH3NH3PbI3 perovskites revealed by coherent acoustic phonons"
"Despite the great amount of attention CH3NH3PbI3 has received for its solar cell application, intrinsic properties of this material are still largely unknown. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. We apply this method to characterize a CH3NH3PbI3 single crystal. We measure the acoustic phonon properties and characterize electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. Our results reveal high electron and hole mobilities of 2,800 and 9,400 cm2 V−1 s−1, respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH3NH3PbI3."
The Scheblykin Group has published a new article in ACS Omega entitled Macroscopic Domains within an Oriented TQ1 Film Visualized Using 2D Polarization Imaging
"Large-area self-assembly of functional conjugated polymers holds a great potential for practical applications of organic electronic devices. We obtained well-aligned films of poly[2,3-bis(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) using the floating film transfer method. Thereby, a droplet of the TQ1 solution was injected on top of the surface of an immiscible liquid substrate, at the meniscus formed at the edge of a Petri dish, from where the polymer solution and the film spread in one direction. Characterization of the TQ1 film using the recently developed two-dimensional polarization imaging (2D POLIM) revealed large, millimeter-sized domains of oriented polymer chains. The irregular shape of the contact line at the droplet source induced the appearance of disordered stripes perpendicular to the spreading direction. A correlation of polarization parameters measured using 2D POLIM revealed the microstructure of such stripes, providing valuable information for further improvement and possible upscaling of this promising method."
Photonics Sweden Student Award
The award was given for the work undertaken during his masters project at Chemical Physics. His thesis concerned "Compression and Shaping of Femtosecond Laser Pulses for Coherent Two-Dimensional Nanoscopy".
Mastering Morphology for Solution-borne Electronics
Researchers from the Chemistry Department participate in a new project that has been granted 28 MSEK support by the Knut and Alice Wallenberg Foundation.
Professor Ivan Scheblykin (Chemical Physics) and University Lecturer Petter Persson (Theoretical Chemistry) from the Chemistry Department at Lund University participate in a new project ”Mastering Morphology for Solution-borne Electronics” that has been granted 28 MSEK support by the Knut and Alice Wallenberg Foundation (2016-10-05). The goal of the new project is to make efficient solar cells from molecular semiconductors through improved processing technology and better understanding of how the fundamental molecular interactions govern the structure in these functional materials. The project is a collaboration between researchers from Karlstad University, Lund University, Chalmers, and Linköping University led by Professor Ellen Moons in Karlstad. The research at the Chemistry Department in Lund will focus on material characterization through a combination of spectroscopy, microscopy and computational chemistry.