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... is the leading theme of our research. We use light to study the structure of molecules and to understand how structure and function are related. To reach this goal we employ several strategies. Starting from isolated molecules in the gas phase that we study with high-resolution molecular beam (single and double resonance) techniques based on fluorescence and multiphoton ionization, we answer questions as to how the conformational landscape looks like in ground and electronically excited states and how changes in electronic charge distribution induce changes in structure and functionality. We then study the effects of a medium by microsolvation where we dress molecules in a molecular beam with a controlled number of solvent molecules, and look how the properties of the individual molecules are affected, ultimately relating these results to molecular properties under low-resolution solution conditions. We complement these experiments with quantum chemical calculations that not only provide us with a solid basis for their interpretation but also suggest new experiments and ways to optimize functional properties. One of the great challenges in the field - and one that we have met successfully - is to extend the complexity of molecules that can be studied in this way from merely model chromophores to genuinely prototypical systems in molecular photobiology or for applications within, for example, molecular nanotechnology.
Structure, and thereby function, is not a static molecular property; it is a property that can be influenced by external stimuli (photons, electrons, etc.), and under non-isolated conditions it is constantly subject to external interactions. We develop and apply new methods based on light to observe structure on time scales ranging from femtoseconds to seconds, ultimately aiming to control the directionality of structure changes through manipulation of intra- and intermolecular interactions in functional materials.
We thus use the interaction between light and molecules to understand , design , and control molecular systems, and seek to cover the complete trajectory from conception of new molecular systems to their application in functional materials. Our research can therefore certainly not be associated exclusively with one of the traditional areas within chemistry or physics, but supersedes their boundaries. Scientific areas that we work in concern:
Een meer populaire beschrijving van het onderzoek dat bij Molecular Photonics wordt gedaan wordt gegeven in een van de 'Onderzoek uitgelicht' afleveringen.
A more popular description of the research in Molecular Photonics can be found in one of the 'Focus on Research' issues.
We regularly have vacancies on new projects. Have a look at the Vacancies page, and make your choice!
We are always interested in enthusiastic MSc en PhD students. For MSc students we regularly have projects that can be filled in on an ad hoc basis. The subjects of these projects reflect the broad scientific area in which Molecular Photonics is working: from more synthetically-oriented projects to high-resolution spectroscopy and advanced femtosecond laser spectroscopic techniques. At the same time, such projects can be rather fundamental in nature but we also have projects that are much more application oriented such as projects that we carry out together with medical centers such as the AMC and the LUMC.
For PhD students we do not have at the moment any position open. However, if you have the possibility to acquire your own funds to finance your PhD research we are always interested to get into contact with you and see how we can work together.
Mechanically interlocked molecules can exhibit molecular chirality that arises due to the mechanical bond rather than covalent stereogenic units. Developing applications of such systems is made challenging by the absence of techniques for assigning the absolute configuration of products and methods to probe how the mechanical stereogenic unit influences the spatial arrangements of the functional groups in solution. In a very fruitful collaboration with Stephen Goldup (University of Southampton) we show in the article "Vibrational circular dichroism spectroscopy for probing the expression of chirality in mechanically planar chiral rotaxanes" published in Chem. Sci. 11, 8469-8475 (2020) for the first time that VCD can be used to not only discriminate between mechanical stereoisomers but also provide detailed information on their (co)conformations. The latter is particularly important as these molecules are now under investigation in catalysis and sensing, both of which rely on the solution phase shape of the interlocked structure. Important as well is the conclusion that even such large and complex systems as rotaxanes have now come within reach of VCD. Pushing the boundaries of what many thought to be too difficult to cross!
The self-assembly proceess of supramolecular chiral polymers is of extensive interest, both from a fundamental as well as applied point of view. In our article "Self-Assembly of Supramolecular Polymers of N‑Centered Triarylamine Trisamides in the Light of Circular Dichroism: Reaching Consensus between Electrons and Nuclei" with the group of Nicolas Giuseppone (University of Strasbourg) that has been published in J. Am. Chem. Soc. 142, 1020−1028 (2020) we we probe the self-assembly process of a prototypical supramolecular building unit by ECD, but in particular by Vibrational Circular Dichroism (VCD). In combination with quantum chemical calculations of these spectra for monomers and oligomers we show how the comparison with experimental results allows us to characterize the supramolecular assemblies in great detail, and highlight the sensitivity of the two techniques to different aspects of molecular and polymeric structure. VCD goes large!
Using dydrogesterone (64 stereoisomers associated with its 6 stereo centres) as a prototypical example we show in our article "Analytical chemistry on many-center chiral compounds based on Vibrational Circular Dichroism: absolute configuration assignments and determination of contaminant levels" (Anal. Chim. Acta 1090, 100-105 (2019)) that based on a single measurement one can determine the absolute configuration of chiral systems with a much larger number of chiral centers than possible before. Further, using studies on mixtures of stereoisomers we also demonstrate that with one single VCD spectrum it is possible to (i) identify the components present in the mixture, and (ii) to determine stereochemical impurity levels as low as 5%. A nice detail is the co-authorship of four bachelor students that contributed to this work during their second-year research project. VCD at work for Analytical Chemistry!
The flexibility of a molecule has important consequences on its function and application. Vibrational Circular Dichroism (VCD) is intrinsically an excellent experimental technique to get a hold on this flexibility as it is highly sensitive to key conformational details and able to distinguish rapidly interconverting conformers. One of the major challenges in analyzing the spectra by comparison to theoretical predictions is the uncertainty in the computed energies of the multitude of conformations. In a fruitful collaboration with Sergio Domingos we present in the Edge article “Taming conformational heterogeneity in and with Vibrational Circular Dichroism spectroscopy” (Chem. Sci. 10, 7680-7689 (2019)) a novel approach that explicitly takes the energy uncertainties into account in a genetic algorithm based method that fits calculated to the experimental spectra. Once again, our Portugese connection in collaboration with Mark Koenis has allowed us to produce a beautiful issue cover of Chemical Science!
Light is an ideal means to control the properties of materials at the molecular level. Over the years many photoswitches have been developed but they are still far from ideal. Ideal photoswitches are operated with visible light only, show large separation of absorption bands and are functional in various solvents including water, posing so far an unmet challenge. Together with groups from Groningen, Florence and Nantes we show in our Nature Communications article "Iminothioindoxyl as a molecular photoswitch with 100 nm band separation in the visible range" (Nature Communications 10, 2390 (2019)) an entirely new class of photoswicthes that meet these 'holy grail' demands. These are extremely versatile systems that open up a complete new application area. The future is bright - and in the visible!
We have used 'fast' IR spectroscopic techniques to find out what actually happens after the initial photoisomerisation step of DASA switches that we previously investigated using femtosecond time-resolved IR absorption spectroscopy. In our article "Taming the Complexity of Donor–Acceptor Stenhouse Adducts: Infrared Motion Pictures of the Complete Switching Pathway" that was published in the J. Am. Chem. Soc. 141, 7376−7384 (2019) we recorded IR movies on the milisecond to hours timescale. 'Subtitles' provided by advanced quantum chemical calculations have now allowed us to follow the entire switching pathway which tuns out to be much more complex than assumed originally. The nice thing is that we now really have an instruction manual of these types of switches in our hands that will allow target-oriented development of novel switches. At a completely different level: check out the cover page of one of the issues of JACS that features graphic artwork made by Kaja Sitkowska!
As part of a consortium of academic and industrial groups from the UK, France, Germany, Spain, and The Netherlands we have received a large grant for a program coordinated by Vasilios Stavros at the University of Warwick that will improve crop yields by protecting plants from cold stress and stimulating their growth under a range of growing conditions. In the coming four years we will work together in a truly exciting mutidisplinary program that combines expertise from biologists, physicists, chemists, toxicologists, and companies aiming for sustainable agricultural methods. We will definitely learn a lot of new things! What is equally nice to see is that the basis of the program stems from very fundamental (but advanced) molecular spectroscopy that is now being used for societal needs.
We go biological! In a nice collaboration with dr. Teun Munnik (SILS, UvA) we are combining our expertise to improve the cold resistance of plants. The first results are very promising but for further commercial development more research is needed. The grant that we received from the Physics2Market program of the Innovation Exchange Amsterdam now allows us to make detailed studies of the plant's temperature profile using a highly sensitive IR camera, and to make quatitative studies of the growth of plants with and without our magic tricks!
Together with our 'partners in crime' from Groningen, Nantes, and Firenze with whom we have set up a very rewarding collaboration, our article "Solvent Effects on the Actinic Step of Donor–Acceptor Stenhouse Adduct Photoswitching" has been published in Angew. Chem. Int. Ed. 57, 8063 (2018). In this work we employ spectroscopic analyses and TD‐DFT calculations to reveal changing solvatochromic shifts and energies of the species involved in DASA photoswitching. Remarkably, we find that although solvents strongly influence the overall photoswitching of DASAs, the kinetics of the actinic step is only slightly perturbed.
Our Communication " Photo-induced pedalo-type motion in an azodicarboxamide-based molecular switch" has been published in Angew. Chem. Int. Ed. 57, 1792 (2018) with a very nice front cover made by our Portugese designer that has once more succeeded to highlight the UvA logo. More important, however, is that we propose a novel type of switch that requires a minimal amount of volume to switch and is therefore an excellent building block for molecular machinery that needs to operate under confined conditions. Molecular bikes made in Spain, Germany and the Netherlands are on their way !
During a scientific project meeting held Friday February 2 at the Molecular Photonics laboratories of the University of Amsterdam's Van 't Hoff Institute for Molecular Sciences, a unique novel Vibrational Circular Dichroism spectrometer was inaugurated for the research project 'Development of an analytical Vibrational Optical Activity toolbox' financed by the NWO Innovation Fund Chemistry. Started in 2015, the research project aims at developing VCD spectroscopy into a genuinely widely applicable analytical method. VCD has great potential for determining solution-state structure and conformation as well as absolute configuration of chiral (bio)molecular systems in general, and of chiral components of smart materials in particular. It was very nice to have Dr Marijn Goes (Sr. Policy Officer NWO) present as well as Dr Rina Dukor (CEO BioTools) and Prof. Larry Nafie (CTO BioTools) !
Our article "Transient two-dimensional vibrational spectroscopy of an operating molecular machine" has been published in Nature Communications 8, 2206 (2017). Here, we show that transient two-dimensional infrared (T2DIR) spectroscopy makes it possible to monitor the conformational changes of a translational molecular machine during its operation.
We have recently started to work in a new exciting research area focussed on novel switches based on donor–acceptor Stenhouse adducts (DASAs). Together with synthetic, computational, and spectroscopic groups from all over Europe the first results have now appeared in the form of the Communication "Shedding Light on the Photoisomerization Pathway of Donor–Acceptor Stenhouse Adducts" in J. Am. Chem. Soc. 139, 15596–15599 (2017). And there is much more to come !
Together with the group of Prof. Melanie Schnell at DESY, and in particular with our former PhD student Dr. Sergio Domingos, and with the group of Prof. Ben Feringa at RUG the communication "Cold snapshot of a molecular rotary motor captured by high-resolution rotational spectroscopy " has been published in Angew. Chem. Int. Ed. 56 , 11209–11212 (2017), the article being selected as well for the front cover. Sergio set a new world record -the studied molecule was the largest molecule investigated by high-resolution microwave spectroscopy to date- but, more importantly, his studies revealed how the individual parts of the motor are constructed and arranged with respect to each other. These studies are exciting as they open up the possibility to study the dynamics of these molecular motors.
Together with the Dutch company MassSpecpecD we have been awarded a KIEM grant by the Netherlands Organisation for Scientific Research (NWO) within the programme High Tech Systems and Materials. With this grant we will develop an enhanced version of the Amsterdam Piezo Valve, a device for generating high frequency pulsed atomic and molecular beams.
May 1, 2017 Prof. Wybren Jan Buma has been appointed to the special chair in Spectroscopy of Photoactive Molecules and Materials at Radboud University’s Faculty of Science. Over the years a very fruitful collaboration has been developed between Molecular Photonics and the spectroscopic groups at FELIX and the Radboud University. This appointment will definitely give further impetus to this collaboration and lead to new exciting research!
Molecular Photonics has been quite successful in obtaining funding for its astrochemical research. Annemieke Petrignani received a grant to appoint a PhD student on the project 'The reaction dynamics of ionic and neutral PAHs' while Wybren Jan Buma and Anouk Rijs (RU) got the project 'High-resolution vibrational and electronic spectroscopy of the isolated aromatic universe' funded. Certainly with in the back of our minds that next year the James Webb Space Telescope will be launched and collect data with an unprecedented spectral and spatial resolution there are exciting times to come!
In recent years we have been quite active in the field of molecular nanotechnology which has attracted this year special attention because of the award of the 2016 Nobel Prize in Chemistry to Sauvage, Fraser Stoddart, and Feringa. It was quite gratifying that one of our studies together with the group of Ben Feringa on one of his famous molecular rotors got accepted just around the time that the Nobel laureates were announced. Our studies using time-resolved IR spectroscopy show that conversion of photon energy into directed motion proceeds on the potential energy surfaces of two different electronic states, which is the more important as it implies that the conical intersection between the ‘dark’ electronically excited state and the ground state determines the efficiency of the motor. Not surprisingly, the article was immediately taken as one of the ACS Editor’s choices!
The interaction of delocalized pi-electrons with molecular vibrations is key to charge transport processes in pi-conjugated organic materials based on aromatic monomers. Yet the role that specific aromatic motifs play on charge transfer is poorly understood. In our article "Electron-flux infrared response of varying pi-bond topology in charged aromatic monomers" published in Nature Communications 7, 12633 (2016) we show that the molecular edge topology in charged catacondensed aromatic hydrocarbons are responsible for spectacular differences in transport properties, allowing for smarter design of new materials. Great work showing off the tremendous (and unique) benefits of the Free Electron Laser facility FELIX !
High-resolution laser spectroscopy for astronomy ! Molecular spectroscopy has been at the basis of the identification of PAHs in the interstellar medium. Their spectroscopic signatures are nowadays used as sensitive probes for the physical and chemical conditions in various astrophysical environments and for the evolution of cosmic carbon. In our article "High-resolution IR absorption spectroscopy of polycyclic aromatic hydrocarbons: the realm of anharmonicity" in Astrophys. J. 814, 23 (2015) we report high-resolution studies that show that these fingerprints are far more complex than assumed so far and that models employed so far to analyse astronomical data are inadequate. Our results have led to quite some shock waves in the astronomical community ...
Our work on amplifying VCD signals by manipulating the "electronics" of chiral molecules and using this amplification for zooming in on their spatial structure has attracted quite a lot of interest. As a results, the Editors of ChemPhysChem have asked us to write a Concepts Article on this subject that has appeared as ChemPhysChem 16, 3363 (2015). Everything you wanted to know about boosting your VCD signals but were afraid to ask is here! Great cover picture as well! If you look carefully, you will see where the work has been done ...
We have been successful again in this competitive program! Together with Luuk Visscher and Roberta Croce (VU University Amsterdam) we obtained a grant for the project Renewable fuels by tuning nature. In this project we aim is to go beyond idealized models as was done before and study fully atomistic models of real biological systems. This will provide the insight needed to propose modifications that can lead to improved biofuels production. The theoretical work focuses on extending the subsystem DFT approaches developed in the Visscher group and is complemented by synthetic and spectroscopic work carried out in the groups of Roberta Croce (Biophysics of Photosynthesis, VU) and the Molecular Photonics group. Theory together with experiment: unbeatable!
Molecular Photonics goes astronomical ! Annemieke Petrignani, with whom we collaborate now for some years in the context of the Dutch Astrochemical Network, has acquired a VIDI grant on the proposal "Shapes and sizes of extraterrestrial organic molecules". This project will be performed in close collaboration with the FELIX laboratory at the Radboud University and our group at the University of Amsterdam. For the course of the Vidi project her research group will be embedded in the Molecular Photonics group.Have a look at the openings she has on the Vacancies page.
Azobenzene can be considered as one of the most prominent examples of photoactive compounds that have found their way into many light-driven technological applications. Despite its extensive use, the fundamental photodynamical processes ocurring after excitation of azobenzene are still subject of vigorous debates. In our article " Fast photodynamics of azobenzene probed by scanning excited state potential energy surfaces using slow spectroscopy" published in Nature Communications 6, 5860 (2015) we take a different approach than the ones in the time domain that have predominantly been followed in the last decades. Instead, we show that frequency-resolved studies with nanosecond lasers are able to (a) settle the debate on which pathway is followed during isomerisation and (b) obtain "high-resolution" spectra of states that live a mere 170 fs. This is quite exciting as it is clear that the same methodology has great potential for many other photoactive compounds that so far have been considered as inaccessible to high-resolution spectrosocopy. And, we finally succeeded in luring Francesco Zerbetto, with whom we have been working for a long time on various molecular spectroscopic challenges, back into fundamental molecular spectroscopy !
Together with the Theoretical Chemistry group of Prof. Luuk Visscher at the VU University Amsterdam and the companies Scientific Computing & Modelling N.V. (The Netherlands) and BioTools, Inc. (USA) we have received a substantial grant for the development of a user-friendly analytical tool for determining the absolute configuration of chiral molecules using Vibrational Circular Dichroism. In this project spectroscopic methods will be integrated with theoretical modelling of molecules.The public-private partnership with the companies involved is aimed to make the tool accessible for application in industry. We are very pleased that we will be working together on this project with Prof. Larry Nafie, one of the pioneers in the field and Chief Technological Officer of BioTools, Inc.!
In a nice collaboration with Koop Lammertsma and Matthias Bickelhaupt (VU University Amsterdam) we obtained a grant for the project Solar Energy Conversion – Breaking the 700 nm Absorption Barrier. In this project we will develop novel molecular systems with optimal characteristics to absorb the 700-1000 nm region of the solar spectrum and convert it to energy. The design of these systems will in first instance be done using a theoretical approach, but importantly, we will also benchmark these calculations with advanced spectroscopic studies.This collaborative effort once more illustrates the added value of a concerted theoretical and experimental approach.
The article on sunscreens has caught the attention of high-impact journals! Nature Chemistry has dedicated a News and Views article on it. Apart from the attention this particular work receives, it is very nice that the article recognizes and emphasizes the role of fundamental science in technological applications.
Our article " Excited state dynamics of isolated and microsolvated cinnamate-based UV-B sunscreens" has been published in J. Phys. Chem. Letters 5, 2464-2468 (2014). We show that in this commonly used class of UV-B filtering agents electronic energy is dissipated at a much slower rate than assumed so far. The presence of such a bottleneck provides an elegant explanation for reported adverse effects. At the same time, we find that one can remove this bottleneck by putting the agent into a watery environment. The work once more shows how very fundamental spectroscopy can have major contributions to an area that generally is not associated with molecular beam spectroscopy. As you can see below, this is a subject that attracts a lot of attention!
In our article "Amplified vibrational circular dichroism as a probe of local biomolecular strucure" we show that one can use auxiliary electronic manifolds (in the present case provided by CoII ions) to enhance vibrational circular dichroism signal intensities. We find that amplification factors of more than two orders of magnitude can be obtained, bringing vibrational differential absorption on an equal footing with electronic differential absorption. Our approach gives us much faster access to the stereochemistry of chiral molecular systems, but also opens up new venues to probe on a very local scale the spatial structure of large systems such as metalloproteins. By the way, nice example of added value of in-house collaborations, in this case between the Molecular Photonics and Homogeneous Catalysis groups ! And, of course, also the collaboration with Larry Nafie is one that we appreciate very much !
Superfluidity is one of the most well-known properties of liquid helium below the so-called critical temperature. But does this still hold for helium nanaodroplets, a medium of increasing interest both from a fundamental as well as applied point of view? In this study in which the experimental expertise of the group of Marcel Drabbels at the EPFL and our own group is combined with the theoretical expertise of the group of Manuel Barranco of the Universitat de Barcelona we have determined for the first time that there also exists a critical Landau velocity at the nano scale. The results have been published in Phys. Rev. Letters 111, 153002 (2013). Check out on YouTube some spectacular simulations of the experiments that have been done!
Our article "Water lubricates hydrogen-bonded molecular machines" has been published in Nature Chemistry 5, 929-934 (2013). We have investigated in this study how one can actively control the mechanics of molecular machines. In this case we look at one particular architecture (rotaxanes) and show that we can influence the rate with which the components of the machine move with respect to each other.
Despite decreasing budgets and an increasing number of applications, Molecular Photonics remains successful in acquiring funds to perform high-level research. VCD is one of the most powerful probes of molecular stereochemistry and structure but suffers heavily from the "Law of conservation of misery" as the information content is much richer than with other methods but at the same time much more difficult to obtain. In the 2012-2013 round of the NWO-CW ECHO program Buma and Woutersen received an ECHO grant for the development and application of novel methods to measure Vibrational Circular Dichroism (see also Vacancies page). As a personal note I can add that my wife (Roberta Bursi, one of the PhD students of one of the godfathers of VCD, the late Philip J. Stephens) thus finally got her way to let me work on VCD as well ...
In Februari 2013 I have been bestowed the immense honor of being awarded the lectureship established in honor of Bryan E. Kohler, one of the giants in the field of molecular spectroscopy who has made a huge impact in the field of the spectroscopy of polyenes. I feel very humble and flattered when looking at the extensive list of previous holders of this lectureship.
As a result of being selected in a competitive program for Graduate Schools, the HRSMC has received in September 2012 funding (800 kEuro) from the Dutch Research Council (NWO) to offer young top talents the possibility to participate in the programme "Sustainability: the molecular approach". In the final stage of the Master Programme, students are challenged to develop their own ideas within the framework of the programme into a PhD research proposal.
Together with the Physical Chemistry group of Prof. M.H.M. Janssen (Free Univerty Amsterdam) the Molecular Photonics group has received a substantial equipment grant for the proposal "Photons for Chemistry". BAZIS grants are grants for research groups that have been recognized as belonging to research priority areas in the Physics and Chemistry sector plans. The grant enables us to update and extend our laser infrastructure that is at the basis of our understanding of the interaction between light and matter. In particular, it allows us to go full speed ahead on our program to translate this understanding into innovative molecular systems and materials with user-defined properties. Moreover, since the equipment is part of LaserLab Amsterdam also external users will have significant advantages from this extensive overhaul of equipment. We hope to see you make use of it soon!
For some time now we are using Vibrational Circular Dichroism (VCD) to study molecular stereochemistry and conformational structure. VCD is very powerful tool but generally suffers from small signal intensities that impede application of the technique as a standard analytical tool. Strategies to enhance VCD signals are therefore of substantial importance. In this Communication we show that we can obtain an order of magnitude enhancement by carefully modulating the electronically excited-state manifold. The article has received quite some attention, not in the least because it was given ample publicity on the back cover of the issue of Chemical Communications in which it appeared!
September 21 marked the official opening of Institute Quantivision, a collaboration between the VUmc, AMC,NKI/AVL, VU, UvA and companies to develop medical imaging devices, software and protocols to enhance the efficiency, efficacy and economy of healthcare. Prof. dr Wybren Jan Buma is one of the members of the Management Team. This Institute has originated from a ZONmw initiative, called Innovative Medical Devices Initiative to establish regional Centres of Research Excellence, where healthcare, business and science collaborate on the development of new medical devices that enable future health care at high standards, in an aging population with decreasing numbers of working forces. We are very excited to be part of this Institute and are looking forward to bring in our Molecular Photonics expertise.
One of the more applied areas the Molecular Photonics group has started to work in, is the area of Medical Photonics. Presently, we have a large portfolio of joint projects with various University Medical Centers that started with the, by now long-standing, fruitful collaboration with the Biomedical Engineering and Physics group at the Amsterdam Medical Center (AMC). Two typical examples are included here; one which concerns a study on new methods for age determination of blood stains that was published in PLos ONE, and one which focuses on the development of new upconversion nanoparticles for applications like photodynamic therapy that was published in the Journal of Physical Chemistry Letters
The Molecular Photonics group has been very succesful in the 2010-2011 ECHO round of the Netherlands Organisation for Scientific Research (NWO). Both Sander Woutersen and Wybren Jan Buma were awarded ECHO grants for research on molecular machines. ECHO grants are €260,000 project grants designated for Excellent CHemical Research projects . ECHO grants are designed to facilitate high-quality research projects rooted in intellectual curiosity. This will allow for the development of audacious ideas, and help lay the groundwork for the research themes of the future and/or scientific innovation.
In a very nice and fruitful collaboration with the groupof Tom Gregorkiewicz (WZI, UvA) silicon nanocrystals have been studied. The resulting article " Red spectral shift and enhanced quantum efficiency in phonon-free photoluminescence from silicon nanocrystals " has been published in Nature Nanotechnology 5 , 878-884 (2010). The article has been highlighted in the News and Views section of the issue.
The continuing collaboration with the group of Dr. Marcel Drabbels at the EPFL has led to an article entitled " IR spectroscopy of molecular ions by nonthermal ion ejection from helium nanodroplets " which has been published in the Journal of the American Chemical Society 132 , 14086-14091 (2010) as a regular article. We report experiments that have enabled the detection of IR absorption in cold molecular ions with a sensitivity that is at least two orders of magnitude better than what was possible up till now. The experiments are the first of its kind in which helium nanodroplets are applied to obtain vibrational spectra of molecular ions.The results hold great promise for the future as was recognized by Chemistry World which highlighted this publication!
Our article " Operation Mechanism of a Molecular Machine Revealed Using Time-Resolved Vibrational Spectroscopy " has been published in Science 328 , 1255-1258 (2010). In this article we look at the mechanical behavior of molecular-level machines using vibrational transitions as probes for determining how the parts of the machines move with respect to each other. More detailed information can be found in the link indicated below
Our Communication " Controlled hydrogen-bond breaking ina rotaxane by discrete solvation " has been published in Angewandte Chemie Int. Ed. 49 , 3896-3900 (2010). It has been selected as one of the highlights with an artful frontispiece made by one of the authors, Dr. Nadja Saendig. This article, in which we show how to release the macrocycle from the thread by solvating a rotaxane with one solvent molecule at a time, has attracted quite some attention. Look at the YouTube link to see a movie of what is happening!
In our Communication " High-resolution excitation and absoption spectroscopy of gas-phase p-coumaric acid: unveiling an elusive chromophore " in the Journal of the American Chemical Society 132 , 6315-6317 (2010) we report on high-resolution spectroscopic studies of isolated para-coumaric acid (pCA). Since this molecule is the chromophore of the Photoactice Yellow Protein (PYP), many studies have - unsuccessfully - pursued the characterization of its electronically excited-state manifold under isolated-molecule conditions. Using a multicolor resonance-enhanced multiphoton ionization approach under molecular beam and helium nanodroplet conditions, we show how pCA has become accessible to high-resolution studies of its conformational and electronically excited states dynamics. Another nice aspect is the participation of two undergraduate students. Good publicity for Chemistry indeed!
A new collaboration has been set up with Dr.Marcel Drabbels (EPFL) in the field of helium nanodroplet spectroscopy. The Communication " Conformational flexibilityof a rotaxane thread probed by electronic spectroscopy in helium nanodroplets " in the Journal of the American Chemical Society 131 , 12902-12910 (2009) reports our first successful studies in this field. We show how dissolving single rotaxane threads into a helium nanodroplet enables us to resolve the broad absorption spectrum observed under molecular beam conditions into the separate contributions of individual conformers populated under the employed experimental conditions. This is a big step forwards as it allows us to study the properties of each single conformer instead of a property averaged over many conformers.
Our Communication " Stiff, and sticky in the right places: binding interactions in isolated mechanically interlocked molecules probed by mid-infraredspectroscopy " has been published in the Journal of the American Chemical Society 131 , 2428-2429 (2009). In a very nice collaboration with FOM Rijnhuizen which gave us access to the unrivaled IR laser radiation possibilities that FELIX offers, we show how we have brought multi-component systems - and with that many other molecular systems that many previously thought to be out of the question - within reach of high-resolution IR spectroscopic techniques.
Together with Robert W. Field (MIT) we have investigated the famous case of InterSystem Crossing (ISC) in acetylene. Employing an experimentally challenging approach based on 2D excited-state photoelectron spectrocopy, we have been able to determine the composition of coupled singlet and triplet wavefunctions. Remarkably, we find interferences between singlet-triplet coupling pathways. This observation opens up exciting possibilities for external control schemes over nonradiative decay pathways. The results have been published as " Interference in acetylene intersystem crossing acts as the molecular analog of Young's double slit experiment " in the Proceedings of the National Academy of Sciences of the United States of America 106 , 2510-2514 (2009).
EXPERIMENT NL (NWO research projects for the general public) is the third book in the series " Science in The Netherlands ". In 14 chapters more than 100 remarkable research projects are presented as the best that Science in The Netherlands offers.In Carpet of Nanomachines our work on rotaxanes is discussed.
In a fruitful collaboration with synthetic, physical-organic, and molecular spectroscopy groups we have shown that photoinduced proton transfer in 7-(2'-pyridyl)-indole is accompanied by mutual twisting of the pyridyl and indole moieties. The results suggest that this phenomenon is quite general for several classes of organic molecules with intramolecular hydrogen bonds. The results have been published as the communication" Protontransfer with a twist? Femtosecond dynamics of 7-(2-pyridyl)indole in condensed phase and in supersonic jets " in Angewandte Chemie Int. Ed. 47 (32),6037-6040 (2008).
Our Communication " Shaping of a conformationally flexible molecular structure for spectroscopy " has been published in Angewandte Chemie Int. Ed. 47(17) , 3174-3179 (2008). It has been selected as one of the highlights, and been published with a very nice frontispiece made by one of the authors, Dr. Anouk Rijs. For highlights of this paper, see for example " Moleculaire mal dwingt grote moleculen in vorm " by Margriet van der Heijden in NRC Handelsblad,April 12, 2008, and the links given below.
March 12, 2008 we received in Brussels the Descartes Prize for Transnational Collaborative Research as member of the SynNanoMotor consortium for" developing the first functional examples of synthetic motors on a molecular scale and many other useful and innovative nanomachines ". This has generated a lot of positive publicity, a few examples of which are given below.
At the annual meeting of the Study group Spectroscopy and Theory of NWO-CW (Netherlands Organization for Scientific Research- Chemical Sciences) Prof. Silvia Volker has retired as chairwoman of the Board, and has been succeeded by Prof.Wybren Jan Buma
As of January 1, 2008 Prof. Kees Elsevier has resigned as Scientific Director of the Holland Research School of Molecular Chemistry (HRSMC), and Prof. Wybren Jan Buma has been appointed as his successor. Kees has done a wonderful job last years and has guided us through the reaccreditation. I'll do my best to live up to his performance!