Photochemistry articles within Nature Chemistry

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  • News & Views |

    Due to the high oxidation potential of gold, the development of dual gold/photoredox-catalysed processes has been limited by the need for an easily reduced radical source. Now, discovery of an energy transfer photoexcitation process overcomes this limitation, enabling the oxidative addition of iodoalkynes onto organogold intermediates.

    • Euan B. McLean
    •  & Ai-Lan Lee

  • Article |

    Studies into gold-catalysed cross-coupling reactions have expanded over recent decades; however, oxidative addition to gold(i) complexes remains challenging. Now it has been shown that a dual catalytic transformation involving iridium photosensitization to trigger oxidative addition to organogold intermediates enables C(sp2)–C(sp) cross-coupling reactions that are useful for the alkynylation of benzofurans.

    • Zhonghua Xia
    • , Vincent Corcé
    •  & Louis Fensterbank

  • Article |

    Super-resolution fluorescence microscopy techniques can interrogate entities that fluoresce; however, most chemical or biological processes do not involve fluorescent species. Now, the incorporation of a competitive reaction into a single-molecule fluorescence detection scheme has been shown to enable quantitative super-resolution imaging of non-fluorescent reactions.

    • Xianwen Mao
    • , Chunming Liu
    •  & Peng Chen

  • Meeting Report |

    Two recent back-to-back meetings conveyed a common set of ongoing challenges for the fields of organocatalysis, photoredox catalysis and photochemistry.

    • Craig P. Johnston

  • News & Views |

    The direct formation of C–N bonds onto arenes provides a simple route to synthesize a variety of important products. Now, formation of a highly polarized, aminium radical cation enables direct C–H amination, allowing the coupling of an exceptionally broad range of alkyl amines and arenes.

    • David Nagib

  • Article |

    The synthesis of aryl amines is traditionally achieved through aromatic nitration or transition metal-catalysed cross coupling. Now, photocatalysis provides a route for the direct and selective C–H amination of aromatics with alkyl amines, without the need for pre-functionalization. This reaction tolerates a variety of functional groups and can be used for late-stage modification.

    • Alessandro Ruffoni
    • , Fabio Juliá
    •  & Daniele Leonori

  • Article |

    The photochemical electrocyclic ring-opening of 1,3-cyclohexadiene is a textbook organic chemistry reaction. Now, using ultrafast electron diffraction its reaction pathway has been resolved on the level of atomic distances and on its natural femtosecond timescale. Furthermore, coherent isomerization dynamics of the photoproduct 1,3,5-hexatriene were observed.

    • T. J. A. Wolf
    • , D. M. Sanchez
    •  & T. J. Martínez

  • Article |

    The SN2 reaction, a fundamental process associated with ionic chemistry, can be incorporated into a photochemical approach to creating radicals from alkyl electrophiles. This method occurs readily under visible-light irradiation, exhibits broad functional-group tolerance, and enables the formation of open-shell intermediates from substrates that are incompatible with traditional radical-generating strategies.

    • Bertrand Schweitzer-Chaput
    • , Matthew A. Horwitz
    •  & Paolo Melchiorre

  • News & Views |

    Covalent organic frameworks (COFs), whose heterogeneous backbones can be easily tuned at the molecular level, are promising photocatalysts for artificial photosynthesis. Sulfone-rich crystalline, wettable COFs have now been shown to exhibit high photocatalytic hydrogen evolution rates with platinum nanoparticles as co-catalysts.

    • Tanmay Banerjee
    •  & Bettina V. Lotsch

  • Article |

    The inherent synthetic tuneability of organic materials makes them attractive in photocatalysis, but they tend to have low quantum efficiencies for water splitting. A crystalline covalent organic framework featuring a benzo-bis(benzothiophene sulfone) moiety has now been shown to exhibit high activity for photochemical hydrogen evolution from water.

    • Xiaoyan Wang
    • , Linjiang Chen
    •  & Andrew I. Cooper

  • Article |

    Enzymes are powerful catalysts for chemical synthesis because they are capable of providing unparalleled levels of selectivity; however, in nature they only catalyse a limited collection of reactions. Now, it has been shown that non-natural reactions that proceed via free-radical intermediates can be catalysed with high selectivity by using an exogenous photoredox catalyst in conjunction with enzymes.

    • Kyle F. Biegasiewicz
    • , Simon J. Cooper
    •  & Todd K. Hyster

  • Article |

    Understanding the mechanism of photoconversion in fluorescent proteins is essential to optimizing applications in imaging and optogenetics. It has now been demonstrated that photoconversion in the photoswitchable protein dronpa follows a multi-step mechanism, with both chromophore and protein structural dynamics occurring on multiple timescales from picoseconds to hundreds of microseconds.

    • Sergey P. Laptenok
    • , Agnieszka A. Gil
    •  & Stephen R. Meech

  • News & Views |

    The beauty and activity of enzymes inspire chemists to tailor new and better non-biological catalysts. Now, a study reveals that the active sites within heterogeneous catalysts actively cooperate in a fashion phenomenologically similar to, but mechanistically distinct, from enzymes.

    • Bert M. Weckhuysen

  • Article |

    The implications of coherence signals for the transfer of energy within the Fenna–Matthews–Olson complex of photosynthetic green sulfur bacteria is a well debated topic. Now, polarization-controlled 2D spectroscopy — aided by vibronic exciton modelling — has enabled the characterization of all such coherences and determination of their physical origins; while electronic coherences dephase extremely rapidly, ground- and excited-state vibrational coherences dominate.

    • Erling Thyrhaug
    • , Roel Tempelaar
    •  & Donatas Zigmantas

  • Article |

    Multi-electron redox reactions are kinetically sluggish; however, plasmonic nanoparticles have shown promise as multi-electron reduction catalysts. Now, the principles that govern the harvesting of multiple electron–hole pairs from plasmonically excited gold nanoparticle photocatalysts are elucidated, providing a general foundation for the plasmonic catalysis of challenging multi-electron, multi-proton chemistry, such as N2 fixation and CO2 reduction.

    • Youngsoo Kim
    • , Jeremy G. Smith
    •  & Prashant K. Jain

  • 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 |

    Spectroscopists and theorists are closing in on an understanding of the origin of oscillatory features in the spectral response of light-harvesting complexes to femtosecond pulsed excitation. Now, the photosynthetic Fenna–Matthews–Olson complex is probed by femtosecond pump–probe spectroscopy and compared with a series of genetically modified mutants with distinct excitonic interactions, allowing electronic and vibrational contributions to coherence to be distinguished.

    • Margherita Maiuri
    • , Evgeny E. Ostroumov
    •  & Gregory D. Scholes

  • Article |

    According to the entatic-state principle, distortions of the coordination geometry of a reacting compound can optimize the energies of starting and final states to improve reaction rates. Here, the entatic-state principle is observed to apply to photoactive copper complexes that have a constrained ligand geometry, resulting in very short charge-transfer state lifetimes.

    • B. Dicke
    • , A. Hoffmann
    •  & S. Herres-Pawlis

  • Article |

    The ability to merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is important for the development of various emerging photonic and optoelectronic technologies. Now, 1-pyrenecarboxylic acid-functionalized CdSe quantum dots have been shown to undergo thermally activated delayed photoluminescence and display tunable photophysical properties.

    • Cédric Mongin
    • , Pavel Moroz
    •  & Felix N. Castellano

  • News & Views |

    The accumulation of multiple redox equivalents is essential in photo-driven catalytic reactions such as solar water splitting. However, direct spectroscopic observation of a twice-oxidized species under diffuse illumination has proved elusive until now.

    • Anna M. Beiler
    •  & Gary F. Moore

  • Article |

    Photosynthesis uses sunlight to oxidize or reduce reaction centres multiple times and prepare them for multiple-electron-transfer reactions. Now, it has been shown that a molecular proxy for a multiple-electron-transfer electrocatalyst can be oxidized twice by dye molecules when both are anchored to a mesoporous TiO2 thin film and excited with low-intensity visible light.

    • Hsiang-Yun Chen
    •  & Shane Ardo

  • Article |

    Providing detailed structural descriptions of the ultrafast photochemical events that occur in light-sensitive proteins is key to their understanding. Now, excited-state structures in the reversibly switchable fluorescent protein rsEGFP2 have been solved by time-resolved crystallography using an X-ray laser. These structures enabled the design of a mutant with improved photoswitching quantum yields.

    • Nicolas Coquelle
    • , Michel Sliwa
    •  & Martin Weik

  • Article |

    Singlet fission — the conversion of one singlet exciton into two triplet excitons, could improve the efficiency of photovoltaic devices — but its mechanism is still to be fully understood. Now, in films of TIPS-tetracene, it has been shown that the formation of the triplet pair state, which has been proposed to mediate singlet fission, is ultrafast and vibronically coherent in this endothermic fission system.

    • Hannah L. Stern
    • , Alexandre Cheminal
    •  & Richard H. Friend

  • News & Views |

    The flow of energy in Earth's primary light harvesters — photosynthetic pigment–protein complexes — needs to be heavily regulated, as the sun's energy supply can vary over many orders of magnitude. Observing hundreds of individual light-harvesting complexes has now provided important insights into the machinery that regulates this process.

    • Peter J. Walla

  • Article |

    Photoprotection is crucial for the fitness of organisms that carry out oxygenic photosynthesis. LHCSR, a photosynthetic light-harvesting complex, has been implicated in photoprotection in green algae and moss. Now, single-molecule studies of LHCSR have revealed that multi-timescale protein dynamics underlie photoprotective dissipation of excess energy.

    • Toru Kondo
    • , Alberta Pinnola
    •  & Gabriela S. Schlau-Cohen

  • 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

  • Article |

    Chiral iminium ions generated from an amine catalyst and enals are key organocatalytic intermediates in thermal asymmetric processes. Now, visible-light excitation of these iminium ions can turn these compounds into strong oxidants to enable enantioselective photochemical β-alkylations of enals with silanes, which are unachievable via conventional ground state pathways.

    • Mattia Silvi
    • , Charlie Verrier
    •  & Paolo Melchiorre

  • 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 |

    Singlet fission — the splitting of a singlet exciton into two triplets — is a process that could be exploited to improve the power conversion efficiency of solar cells. Spectroscopic data now suggest that coherent and incoherent mechanisms for singlet fission in crystalline hexacene coexist and occur on different timescales.

    • Nicholas R. Monahan
    • , Dezheng Sun
    •  & X.-Y. Zhu

  • Article |

    Although ribose aminooxazoline has been shown to be a potential intermediate in prebiotic pyrimidine ribonucleotide synthesis, a route by which this could occur has remained elusive. Now, a remarkably efficient photoanomerization reaction has been investigated by theory and experiment. The new route affords enantiomerically pure ribonucleotides when the starting material is enantioenriched.

    • Jianfeng Xu
    • , Maria Tsanakopoulou
    •  & John D. Sutherland

  • Article |

    Switching the chirality of helicates non-invasively is challenging, even though helicates were discovered some decades ago. Now, by incorporating a light-driven molecular motor into a Cu(I)-helicate, the chirality of the metal helicate as well as the assembly and disassembly processes can be switched non-invasively by light and heat.

    • Depeng Zhao
    • , Thomas van Leeuwen
    •  & Ben L. Feringa

  • Article |

    Reversibly inducing solid-to-liquid transitions of polymers at room temperature represents a challenge for enhanced processability and applications of polymers. Now, three azopolymers have been shown to exhibit photoswitchable glass transition temperatures, resulting in reversible solid-to-liquid transitions. Light exposure can heal cracks in hard azopolymers, reduce surface roughness of azopolymer films and control azopolymer adhesion.

    • Hongwei Zhou
    • , Changguo Xue
    •  & Si Wu

  • 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

  • Thesis |

    Ksenija Glusac takes us on a journey through some of the most important light-driven reactions upon which nature and chemists rely.

    • Ksenija Glusac

  • Article |

    Selectively degrading the pathogenic, aggregated amyloid state of proteins, without affecting the functional state, is a potential therapeutic strategy for treating amyloid diseases. Now, photooxygenation catalysts that are active only when bound to the cross-β-sheet structure of the amyloid form have been developed.

    • Atsuhiko Taniguchi
    • , Yusuke Shimizu
    •  & Motomu Kanai

  • Article |

    A primary objective in solar energy conversion is to achieve long-lived light-driven redox separation. Now a modular self-assembly strategy has been developed to construct molecular p/n junctions surface-bound to transparent conducting ITO nanoparticle electrodes. Both photoanode and photocathode assemblies achieved remarkably long-lived redox separation lifetimes without making use of traditional wide-bandgap semiconductors.

    • Byron H. Farnum
    • , Kyung-Ryang Wee
    •  & Thomas J. Meyer

  • Article |

    Effective light capture in photosynthetic organisms depends on the efficiency of all energy-transfer steps in the photosynthetic unit. Two-dimensional electronic spectroscopy has now been used on intact cells in situ to reveal and characterize the functional connectivity between individual complexes in the photosynthetic apparatus of green sulfur bacteria.

    • Jakub Dostál
    • , Jakub Pšenčík
    •  & Donatas Zigmantas

  • Article |

    Designing improved catalysts is predicated on understanding how they work. Now, by positioning three ruthenium centres in a macrocyclic framework, a remarkable acceleration of catalytic water oxidation has been achieved. Detailed mechanistic studies revealed that the catalyst operates through the ‘water nucleophilic attack’ pathway—similar to the natural oxygen-evolving cluster of photosystem II.

    • Marcus Schulze
    • , Valentin Kunz
    •  & Frank Würthner

  • Article |

    Water oxidation on titanate surfaces is thought to occur via an oxyl-radical intermediate (Ti­–O•), which precedes O–O bond formation, and for which there is indirect evidence. Using ultrafast infrared spectroscopy and theoretical calculations of photocatalytic water oxidation at the n-SrTiO3/aqueous interface, the oxyl radical has now been detected through its subsurface vibration.

    • David M. Herlihy
    • , Matthias M. Waegele
    •  & Tanja Cuk

  • Article |

    An important source of atmospheric hydroxyl radicals is from the dissociation of Criegee intermediates produced in alkene ozonolysis reactions. The dissociation dynamics of the prototypical CH3CHOO Criegee intermediate have now been determined. Complementary experimental and theoretical studies were carried out and the translational and internal energy distributions of the OH radical products were characterized.

    • Nathanael M. Kidwell
    • , Hongwei Li
    •  & Marsha I. Lester

  • Article |

    Metal centres play an important role in the damage to biomolecules caused by radiation, but the respective microscopic mechanisms are unknown. Now it is shown that the absorption of X-rays by a metal ion leads to an intricate chain of ultrafast relaxation steps that results in the complete degradation of the metal's local environment.

    • V. Stumpf
    • , K. Gokhberg
    •  & L. S. Cederbaum

  • 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

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