Optical spectroscopy articles within Nature Chemistry

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  • Article |

    Accessing longer-wavelength emitting organic fluorophores is critical for diagnostic imaging. Here a series of silicon-RosIndolizine fluorophores with emission maxima at 1,300 nm, 1,550 nm and 1,700 nm were synthesized. The fluorophores generate high-resolution in vivo fluorescence images in mice and establish design principles for future shortwave-infrared fluorophore designs.

    • William E. Meador
    • , Eric Y. Lin
    •  & Jared H. Delcamp

  • Article
    | Open Access

    The spontaneous recombination of photogenerated radicals surrounded by solvent molecules is an important energy-wasting elementary step in photoredox reactions. Now the decisive role that cage escape plays in these reactions is shown in three benchmark photocatalytic reactions, with quantitative correlations observed between photoredox product formation rates and cage escape quantum yields.

    • Cui Wang
    • , Han Li
    •  & Oliver S. Wenger

  • Article |

    Chromophore supramolecular assemblies have long been studied for their exotic photophysical properties arising from their local geometry and long-range sensitive excitonic couplings. Now a high-resolution structure of a model nanotubular system has revealed a uniform brick-layer molecular arrangement and a non-biological supramolecular motif—interlocking sulfonates—enabling clear understanding of supramolecular structure–excitonic property relationships.

    • Arundhati P. Deshmukh
    • , Weili Zheng
    •  & Justin R. Caram

  • Research Briefing |

    Trans–cis photoisomerization is a fundamental photochemical reaction that is thought to proceed through an intermediate with a perpendicular conformation. However, unambiguous identification of this state has proved challenging. The combination of state-of-the-art ultrafast spectroscopy and quantum chemical calculations now provides evidence for its structural observation in stilbene photoisomerization.

  • Article |

    The prototypical trans–cis photoisomerization of stilbenes is thought to occur via a transient intermediate with a perpendicular conformation—often called ‘the phantom state’—but its unambiguous identification has thus far proved difficult. Now, using ultrafast ultraviolet Raman spectroscopy and ab initio molecular dynamics simulation, evidence for its existence and its perpendicular conformation has been obtained.

    • Hikaru Kuramochi
    • , Takuro Tsutsumi
    •  & Tahei Tahara

  • News & Views |

    Open-shell organic molecules with properties that can be modulated by external stimuli are of interest for spintronics applications. Now, an overcrowded alkene with open-shell tetraradical character has been synthesized in which the interaction between the π-conjugated subunits depends on the charge and spin state.

    • Yoshito Tobe

  • Article
    | Open Access

    Tetrafluorenofulvalene (TFF) defies conventional rules of bond strength in organic chemistry. In particular, the central alkene bond of TFF becomes stronger in the quintet state and in the tetraanion. These changes arise from the unusual interplay between the twist, aromaticity and spin pairing in the π-electron system of TFF.

    • Bibek Prajapati
    • , Madan D. Ambhore
    •  & Marcin Stępień

  • Article |

    Two-dimensional hybrid perovskites have gained substantial interest recently due to their controllable optoelectronic properties; however precise control over layer thickness has been synthetically challenging. Now a crystal growth method is shown to achieve high-quality single crystals of organic semiconductor-incorporated perovskites with control over their thickness and length through judicious solvent choice, affording precisely tuned optoelectronic properties.

    • Jee Yung Park
    • , Ruyi Song
    •  & Letian Dou

  • Article
    | Open Access

    Although noble metal coordination complexes typically show promising photophysical properties that enable applications in lighting, photocatalysis and solar energy conversion, first-row transition metal complexes rarely display properties as attractive. Now, two Cr(0) complexes are shown to afford excited-state lifetimes of ~50 ns and photophysical properties analogous to noble metal complexes, enabling efficient photoredox catalysis.

    • Narayan Sinha
    • , Christina Wegeberg
    •  & Oliver S. Wenger

  • Article |

    Indole-5,6-quinone (IQ) is a long-sought intermediate and structural subunit of eumelanin pigments whose instability has precluded isolation and characterization. It has now been shown that a sterically shielded derivative of IQ exhibits hallmark eumelanin properties, including near-infrared absorption, ultrafast nonradiative decay and a persistent semiquinone radical formed by comproportionation.

    • Xueqing Wang
    • , Lilia Kinziabulatova
    •  & Jean-Philip Lumb

  • Article
    | Open Access

    The design of photoactivatable fluorophores—which are required for some super-resolution fluorescence microscopy methods—usually relies on light-sensitive protecting groups imparting lipophilicity and generating reactive by-products. Now, it has been shown that by exploiting a unique intramolecular photocyclization, bright and highly photostable fluorophores can be rapidly generated in situ from appropriately substituted 1-alkenyl-3,6-diaminoxanthone precursors.

    • Richard Lincoln
    • , Mariano L. Bossi
    •  & Stefan W. Hell

  • News & Views |

    Over the past 25 years, the photo-induced spin-crossover behaviour of Fe(II) complexes has puzzled scientists. Now, a symmetry-breaking twisting mode has been observed during the relaxation of such a complex. Controlling its configuration using enantiopure counterions has also been shown to slow down the relaxation.

    • J. Olof Johansson

  • Article
    | Open Access

    Ions in salt solutions perturb the hydrogen bonding between the surrounding water molecules, altering the properties of water, but how ion polarity affects this is not fully understood. By monitoring the dissipation of terahertz energy in salt solutions, it has now been shown that intermolecular rotational-to-translational energy transfer is enhanced by highly charged cations and reduced by highly charged anions.

    • Vasileios Balos
    • , Naveen Kumar Kaliannan
    •  & Mohsen Sajadi

  • Article |

    Despite much research, the high-spin-state relaxation mechanism of Fe(II) spin-crossover complexes is unresolved. Using ultrafast circular dichroism spectroscopy it has now been revealed that the spin relaxation is driven by a torsional twisting mode, which breaks the chiral symmetry of a prototypical Fe(II) compound. Stereocontrolling the configuration of the complex can thus be used to slow down the spin relaxation.

    • Malte Oppermann
    • , Francesco Zinna
    •  & Majed Chergui

  • Article |

    In photosynthesis, photoenergy transfers through chromophore-containing proteins, which exhibit thermal fluctuations that change the positions of the chromophores. Now the ultrafast dynamics in allophycocyanin—a cyanobacterial light-harvesting protein—have been measured using single-molecule pump–probe spectroscopy. The data show that energy transfer precedes protein-induced photophysical heterogeneity, ensuring that light harvesting is robust to the heterogeneity.

    • Raymundo Moya
    • , Audrey C. Norris
    •  & Gabriela S. Schlau-Cohen

  • News & Views |

    Transition metal complexes with metal-to-ligand charge transfer (MLCT) luminescence and photoactivity typically rely on precious metals such as ruthenium or iridium. Now, two complexes of the Earth-abundant 3d manganese have displayed room-temperature MLCT luminescence in solution and a unique excited-state reactivity.

    • Katja Heinze

  • Article |

    Manganese(i) is isoelectronic to iron(ii) but has typically been overlooked as a cheap Earth-abundant metal for the development of 3d6 metal-to-ligand charge transfer (MLCT) emitters and photosensitizers. Now, using chelating isocyanide ligands, air-stable manganese(i) complexes have been obtained that exhibit MLCT luminescence, as well as energy- and electron-transfer photoreactivity.

    • Patrick Herr
    • , Christoph Kerzig
    •  & Oliver S. Wenger

  • Meeting Report |

    Chirality is fundamental to chemistry, molecular biology and photonics, but chirality itself is not often in the spotlight. Lewis E. MacKenzie and Patrycja Stachelek report on the 2021 Chiral Materials meeting, which explored how chirality manifests in functional materials, and how it can lead to new technological applications.

    • Lewis E. MacKenzie
    •  & Patrycja Stachelek

  • Article |

    Reactions at the interface between water and other phases play important roles in various chemical settings. Now, ultrafast phase-sensitive interface-selective vibrational spectroscopy has revealed that the photoionization of phenol can occur four orders of magnitude faster at the water surface than in the bulk aqueous phase.

    • Ryoji Kusaka
    • , Satoshi Nihonyanagi
    •  & Tahei Tahara

  • Article |

    The role of the biexcitonic triplet-pair state 1(TT) during triplet–triplet annihilation events in singlet-fission materials has been the subject of recent debate. Now, emissive 1(TT) states have been shown to be direct products of triplet–triplet annihilation in both endothermic and exothermic singlet-fission materials.

    • David G. Bossanyi
    • , Maik Matthiesen
    •  & Jenny Clark

  • Article |

    Conducting high-resolution, multiplexed imaging in living mammals is challenging because of considerable scattering and autofluorescence in tissue at visible and near-infrared wavelengths. Now, real-time, non-invasive multicolour imaging experiments in live animals have been achieved through the design of optical contrast agents for the shortwave infrared (SWIR, 1,000–2,000 nm) region and the introduction of excitation multiplexing with single-channel SWIR detection.

    • Emily D. Cosco
    • , Anthony L. Spearman
    •  & Ellen M. Sletten

  • News & Views |

    Single-molecule magnets are able to store information through their magnetic anisotropy, making them very promising systems for memory applications. Now, femtosecond-laser-initiated molecular dynamics that modulate magnetic anisotropy have been observed, paving the way for operation on ultrafast timescales.

    • Eric Collet

  • Article |

    The broad infrared spectrum of water in the OH stretching region shows how significantly a water molecule is distorted when within a hydrogen-bonding network; it also raises the question of what the spectrum of a single OH oscillator would be. Now, the spectral signatures of isolated OH oscillators embedded in cold water cages have been measured using vibrational spectroscopy.

    • Nan Yang
    • , Chinh H. Duong
    •  & Mark A. Johnson

  • News & Views |

    The structural features and catalytic performances of catalyst particles have now been correlated using a fluorescence microscopy approach, by tracking nanoprobes as well as fluorescent reaction products. Such mapping enables exploration of structure–function relationships, which is essential for the design of better catalysts.

    • Wei Wang

  • Article |

    The accessibility of materials’ porous domains is typically explored through bulk, and often non-visual, measurements. Now, an integrated fluorescence microscopy approach has established a direct visual relationship between pore architecture (which depends on pore sizes and interconnectivity), molecular transport, and in turn catalytic performance in industrial-grade catalyst particles.

    • Gareth T. Whiting
    • , Nikolaos Nikolopoulos
    •  & Bert M. Weckhuysen

  • Article |

    Although ubiquitous throughout chemistry and biology, the structure and transport mechanism of the aqueous proton in solution remain elusive. Through advances in ultrafast broadband 2D IR spectroscopy, the structure of the aqueous proton is revealed to have a charge-delocalized H5O2+ Zundel-like core arrangement with surprisingly persistent structural heterogeneity.

    • Joseph A. Fournier
    • , William B. Carpenter
    •  & Andrei Tokmakoff

  • Article |

    That K+ channels conduct K+ ions at near-diffusion limited rates, but block the passage of smaller Na+ ions, creates an apparent contradiction. Now, atomistic simulations and free-energy calculations are used to show that both K+ permeation and ion selectivity are governed by the direct knock-on of completely desolvated ions in the channels’ selectivity filter.

    • Wojciech Kopec
    • , David A. Köpfer
    •  & Ulrich Zachariae

  • Article |

    Molecular collisions can lead to the absorption of incident light even for transitions that are spectroscopically forbidden for the isolated molecules. Now the electronic–vibrational transitions of O2 have been theoretically studied and, contrary to textbook knowledge, it is shown that the absorption mechanism and the spectral line shape depend on the collision partner, oxygen or nitrogen.

    • Tijs Karman
    • , Mark A. J. Koenis
    •  & Gerrit C. Groenenboom

  • Article |

    Isotope effects provide deep insight into mechanisms of chemical and biochemical processes. Now, it has been shown that the pattern of isotopic substitution of the isomerizing bond of the retinal chromophore in the visual pigment rhodopsin significantly alters the reaction quantum yield—revealing a vibrational phase-dependent isotope effect.

    • C. Schnedermann
    • , X. Yang
    •  & R. A. Mathies

  • Article |

    Singlet fission may one day allow solar cells to produce two excited electrons with one photon. Now, by comparison of the time-resolved photoluminescence and sensitized triplet–triplet annihilation of a tetracene derivative, it has been shown that—contrary to previous reports—the excimer state is a trap, and not a necessary intermediate for singlet fission.

    • Cameron B. Dover
    • , Joseph K. Gallaher
    •  & Timothy W. Schmidt

  • Article |

    Water oxidation is key to the production of chemical fuels from electricity. Now, guided by theory, NiCoFeP oxyhydroxide catalysts have been developed that require an overpotential lower than that required by IrO2. In situ soft X-ray absorption studies of neutral-pH NiCoFeP catalysts indicate formation of Ni4+, which is favourable for water oxidation.

    • Xueli Zheng
    • , Bo Zhang
    •  & Edward H. Sargent

  • Article |

    Realization of the bicyclic aromaticity has attracted much attention because of the potential to modulate the fundamental properties of 3D aromatic organic molecules that are not topologically planar. Now, the synthesis and characterization of dual-aromatic molecules, and their electronically mixed [4n+1]/[4n+1] triplet bi-radical species displaying Baird-type aromaticity, has been realized.

    • Won-Young Cha
    • , Taeyeon Kim
    •  & Dongho Kim

  • Article |

    Octameric complexes of serine are long known for their special properties, such as their enhanced stability and preference for homochirality. Yet, there is no consensus on their structures. Now, experimental data on the serine octamer–dichloride complex is presented that supports a highly symmetrical, highly stable structure.

    • Jongcheol Seo
    • , Stephan Warnke
    •  & Gert von Helden

  • News & Views |

    Femtochemistry, the real-time study of reactions on a timescale that captures the molecular and atomic activity involved, has traditionally been performed in the gas or liquid phase. It has now been extended to the solid state in a study that highlights how a controlled reaction environment can place steric constraints on the motions of photoproducts.

    • Giulio Cerullo
    •  & Marco Garavelli

  • Article |

    Dissociative reactions in the solid state are prone to sample damage. Now, improved sample handling and measurement conditions enable the study of the dissociative reaction of a model triatomic system in the solid state on ultrafast timescales, revealing the significant impact of lattice coordination on the reaction pathway.

    • Rui Xian
    • , Gastón Corthey
    •  & R. J. Dwayne Miller

  • News & Views |

    The process of electronic energy transfer between molecules has long fascinated chemists. Femtosecond spectroscopy measurements of a series of molecular dimers now reveal signals that arise from non-Born–Oppenheimer coupling, suggesting a new mechanism to enhance energy transfer.

    • Daniel B. Turner

  • Article |

    Synthetic heterodimers provide a platform to demonstrate molecular design principles of vibronic coupling. Now, it has been shown that quantum beating caused by vibronic coupling can be controlled by packing a structurally flexible heterodimer on single-walled carbon nanotubes. This quantum beating requires a vibration to be resonant with the energy gap between excited states and structural rigidity.

    • Lili Wang
    • , Graham B. Griffin
    •  & Gregory S. Engel

  • Article |

    Photoreceptors play an essential role in determining the fate of subsequent biological reactions, however, tracking their structural evolution on ultrafast timescales has been challenging. Now, photoactive yellow protein has been studied using time-domain Raman spectroscopy with sub-7-femtosecond pulses, revealing the ultrafast rearrangement of its hydrogen-bonding structure and also the structure of the first photocycle intermediate.

    • Hikaru Kuramochi
    • , Satoshi Takeuchi
    •  & Tahei Tahara

  • Article |

    Ultrafast 2D Raman-THz spectroscopy has been applied to investigate the dynamics of the hydrogen-bond networks in aqueous salt solutions. It was demonstrated that the degree of inhomogeneity of the intermolecular modes of the liquid correlates with the structure-making capability of the cation.

    • Andrey Shalit
    • , Saima Ahmed
    •  & Peter Hamm

  • Article |

    A family of fluorescent molecular rotors has been developed and their mechanism for emission understood. It has been observed that, although most fluorescent molecules emit from their lowest energy excited state, S1 (in accordance with Kasha's rule), BODIHY dyes do not. Furthermore, their fluorescence is enhanced through restricted rotor rotation, which suppresses internal conversion to the dark S1 state.

    • Hai Qian
    • , Morgan E. Cousins
    •  & Ivan Aprahamian

  • Article |

    Difficulties in experimentally achieving simultaneous structural sensitivity and time resolution have hindered the real-time mapping of the vibrational energy relaxation pathways in biomacromolecules. Now, using ultrashort light pulses to locally deposit excess energy in a protein-bound haem, the temporal evolution of the subsequent energy flow has been monitored, unravelling vibrational couplings that lead to mode-specific temperature changes.

    • C. Ferrante
    • , E. Pontecorvo
    •  & T. Scopigno

  • Article |

    Singlet fission in assemblies of molecular chromophores offers a promising route to improving solar cell efficiencies, but its mechanism is not fully understood. Now, a series of covalently bound π-stacked terrylenediimide dimers have been studied to elucidate the role of interchromophore charge-transfer states in the mechanism of singlet fission.

    • Eric A. Margulies
    • , Claire E. Miller
    •  & Michael R. Wasielewski

  • Article |

    Spectral broadening generally conceals the signatures of rotational and translational motion in solution-phase spectra. Now, using highly inert perfluorocarbon solvents, spectral broadening has been minimized allowing the translational, rotational and vibrational relaxation dynamics of highly excited CN solute molecules to be observed simultaneously.

    • Michael P. Grubb
    • , Philip M. Coulter
    •  & Michael N. R. Ashfold

  • Article |

    Photoexcited holes in CdS nanocrystals rapidly trap to the surface and although they are integral to nanocrystal photophysics and photochemistry, their dynamics have remained elusive. Time-resolved spectroscopy and theoretical modelling have now revealed that trapped holes in CdS nanorods are mobile and undergo a random walk on the nanocrystal surface.

    • James K. Utterback
    • , Amanda N. Grennell
    •  & Gordana Dukovic

  • Article |

    Hydrogen fluoride has been encapsulated in C60-fullerene using molecular surgery. The quantum rotor system has been studied by NMR and infrared spectroscopy as well as neutron scattering. The fullerene cage causes a small red-shift in the HF rotational and vibrational constants, and shields around 75% of its dipole.

    • Andrea Krachmalnicoff
    • , Richard Bounds
    •  & Richard J. Whitby

  • News & Views |

    While there is some qualitative understanding of how excess protons behave in acidic aqueous solutions, there is still much to learn about the structures they form with water molecules. Now, 2D infrared spectroscopy has enabled the definite identification of the 'Zundel cation' in protonated liquid water and an approximate determination of its lifetime.

    • Noam Agmon

  • News & Views |

    Vision is initiated by photoisomerization of 11-cis retinal in the visual pigment rhodopsin — a fast and efficient process. Spectroscopic studies now demonstrate that the transition from the reactant photoexcited-state to the ground-state photoproduct, which mediates this important reaction, occurs on a sub-50-fs timescale and is vibrationally coherent.

    • Richard A. Mathies

  • Article |

    The isomerization of the retinal chromophore of rhodopsin is the photochemical process that initiates the sense of vision. Now, heterodyne-detected transient grating spectroscopy has been used to resolve coherent vibrational dynamics during this process, helping to identify strictly local vibrational motions as the origin of the coherent surface crossing, which occurs on a sub-50-fs timescale.

    • Philip J. M. Johnson
    • , Alexei Halpin
    •  & R. J. Dwayne Miller

  • Article |

    Singlet fission, a spin-allowed conversion of a spin-singlet state into a pair of spin-triplet excitons, may be useful for the development of next-generation photovoltaics. Ultrafast coherence measurements now show that vibrational motions play a critical role in fission as they facilitate the mixing of triplet-pair states with singlet excitons.

    • Artem A. Bakulin
    • , Sarah E. Morgan
    •  & Akshay Rao

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