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Theoretical Study on Chemical Structures and Stability of Molecules in Metallic Junctions
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. (Prof. Yi Luo)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, we focus on the structural identification of the interface using surface enhanced Raman spectroscopy (SERS) and inelastic electron tunnelling scattering (IETS). Two different molecular junctions, namely gold/ trans-1,2-bis (4-pyridyl) ethylene/gold junction and gold/4,4'-bipyridine/gold junctions in various conditions were studied and the corresponding configurations were determined. The enhancement in SERS was also studied by employing the time-dependent density functional theory. Furthermore, we studied some properties of the interface, such as the stability of the adsorbates and charge transfer properties of molecular junctions. The decrease in the stability of molecules was found when adsorbed on metallic surface and trapped in metallic junctions. Our studies explained several puzzles and by rational design, more stable molecular devices were obtained.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2016. , 71 p.
Series
TRITA-BIO-Report, ISSN 1654-2312 ; 2016:12
Keyword [en]
SERS, IETS, Interface, Chemical Stability
National Category
Natural Sciences Chemical Sciences Theoretical Chemistry
Research subject
Theoretical Chemistry and Biology
Identifiers
URN: urn:nbn:se:kth:diva-185947ISBN: 978-91-7595-992-4 (print)OAI: oai:DiVA.org:kth-185947DiVA: diva2:924900
Public defence
2016-05-25, FA32, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2016-04-29Bibliographically approved
List of papers
1. Vibrational identification for conformations of trans-1,2-bis (4-pyridyl) ethylene in gold molecular junctions
Open this publication in new window or tab >>Vibrational identification for conformations of trans-1,2-bis (4-pyridyl) ethylene in gold molecular junctions
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2015 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 453-454, 20-25 p.Article in journal (Refereed) Published
Abstract [en]

The surface-enhanced Raman scattering (SERS) spectroscopy and inelastic electron tunneling spectroscopy (IETS) are employed to study trans-1,2-bis (4-pyridyl) ethylene (BPE)/gold system. Both junction and complex forms are considered for the SERS simulations. It is predicted that the peak at 1581 cm-1 is more intense in the junction forms than that in the complex forms. Time dependent density functional theory calculations show that the relative intensity is mainly controlled by the excitation energy derivative respect to the normal modes, and the total intensity is governed by the excitation energy of the excited states. The CH bending modes dominate the IET spectra when BPE adsorbed on the flat gold surfaces. While, the pyridyl ring deformation modes are more active when BPE adsorbed on the edge of the gold clusters. For BPE adsorbed on the tip of gold clusters, the pyridyl ring and CC stretching modes show significant contribution to the IET spectra.

Keyword
IETS, Junctions, SERS, TDDFT
National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:kth:diva-166930 (URN)10.1016/j.chemphys.2015.03.009 (DOI)000354120700004 ()2-s2.0-84927600894 (Scopus ID)
Funder
Göran Gustafsson Foundation for Research in Natural Sciences and MedicineSwedish Research Council
Note

QC 20150609

Available from: 2015-06-09 Created: 2015-05-21 Last updated: 2017-12-04Bibliographically approved
2. Quasi-Analytical Approach for Modeling of Surface-Enhanced Raman Scattering
Open this publication in new window or tab >>Quasi-Analytical Approach for Modeling of Surface-Enhanced Raman Scattering
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2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 52, 28992-28998 p.Article in journal (Refereed) Published
Abstract [en]

Surface-enhanced Raman scattering has become a powerful analytical tool for the characterization of molecules adsorbed on metal surfaces. The lack of reliable computational methods to accurately assign the complicated Raman spectra has hampered its practical applications. We propose here a quasi-analytical method that allows for the effective evaluation of Raman tensors in periodic systems based on density functional perturbation theory and the finite-difference approach. Its applicability has been validated by simulating Raman spectra of 4,4’-bipyridine (4,4’-bpy) in various conditions. The calculated Raman spectra of isolated 4,4’-bpy as well as its adsorption on flat gold surfaces nicely reproduce their experimental counterparts. The same method has also been successfully applied to a more complicated system, namely 4,4’-bpy inside gold nano junctions. By comparing with the in situ experimental spectra, four interfacial configurations are identified, which are further verified by the good agreement between the simulated charge transfer properties and the experimental measurements. These results indicate that the proposed low-cost quasi-analytical method can provide accurate interpretation for the experimentally measured surface-enhanced Raman spectra and unambiguously determine the structures of the molecules on metal surfaces.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2015
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-181476 (URN)10.1021/acs.jpcc.5b09793 (DOI)000367704500031 ()2-s2.0-84953318034 (Scopus ID)
Note

QC 20160202

Available from: 2016-02-02 Created: 2016-02-02 Last updated: 2017-11-30Bibliographically approved
3. Molecular Design to Enhance the Thermal Stability of a Photo Switchable Molecular Junction Based on Dimethyldihydropyrene and Cyclophanediene Isomerization
Open this publication in new window or tab >>Molecular Design to Enhance the Thermal Stability of a Photo Switchable Molecular Junction Based on Dimethyldihydropyrene and Cyclophanediene Isomerization
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2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 21, 11468-11474 p.Article in journal (Refereed) Published
Abstract [en]

Photoswitchable molecular devices based on dimethyldihydropyrene (DHP) and cyclophanediene (CPD) isomers in gold junctions have been systematically studied by using first-principles calculations. The reaction pathways for the forth- and back-isomerization between DHP and CPD have been explored. It is found that along the ground state, the calculated barrier for the back-isomerization from CPD to DHP is as high as 23.2 kcal/mol. The forth- and back-isomerization on excited state was found to be much easier compared to that on the ground state. Our calculations have shown that the same conclusions about the reaction pathways can be drawn for the DHP/CPD derivatives that were experimentally studied. It is revealed that the thermal stability of the molecular switch can be significantly enhanced when certain substitutions are employed. A desirable substitution that gives a larger ON/OFF ratio and higher thermal stability is proposed for these isomeric systems. We have also found that the electrode distance has a huge impact on the electron transport properties, as well as the switching performance, of these junctions, which nicely explains some puzzling experimental observations.

Keyword
Photoinduced Electron-Transfer, Symmetry Forbidden, Gate-Voltage, Temperature, Derivatives, Energy, Photochromism, Polyimides, Complexes
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-169964 (URN)10.1021/acs.jpcc.5b02201 (DOI)000355495600021 ()2-s2.0-84930660675 (Scopus ID)
Note

QC 20150625

Available from: 2015-06-25 Created: 2015-06-25 Last updated: 2017-12-04Bibliographically approved
4. Roles of Plasmonic Excitation and Protonation on Photoreactions of p-Aminobenzenethiol on Ag Nanoparticles
Open this publication in new window or tab >>Roles of Plasmonic Excitation and Protonation on Photoreactions of p-Aminobenzenethiol on Ag Nanoparticles
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 13, 6893-6902 p.Article in journal (Refereed) Published
Abstract [en]

There is increasing evidence that surface plasmons could catalyze photochemical reactions of organic molecules on metal surfaces. However, due to the complex interactions among the substrate, the adsorbate, the environment, and the incident light, the existence and the underlying mechanism of such catalytic processes have been under intense debate. Here we present a systematic first principles study on one of the most studied and controversial systems, namely, p-aminobenzenethiol (PATP) adsorbed on silver nanoparticles. Our calculations have confirmed that the observed surface-enhanced Raman scattering (SERS) bands at 1142, 1391, and 1440 cm(-1) of PATP on silver surfaces belong to its coupling reaction product, 4,4'-dimercaptoazobenzene (DMAB). It is found that the deprotonation or protonation of N atoms is the key initial step for the transformations between PATP and DMAB. The photodecomposition reaction from DMAB to PATP can occur only under the conditions that both proton transfer and plasmonic excitations have taken place. Moreover, in addition to the widely suggested hot-electron injection mechanism of plasmon, a new photochemical channel has been revealed in the decomposition of DMAB molecules under suitable incident light. This may open up an entire new type of chemical reaction in surface chemistry that we call plasmonic photochemistry. Our theoretical calculations provide consistent interpretations for the experimentally observed pH-,wavelength-,and electrode potential dependence of the SERS spectra of PATP/DMAB adsorbed on silver surfaces. Our findings highlight the important role of theoretical investigations for better understanding of complex processes involved in photochemical reaction of surface adsorbates.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
Keyword
Electrode potentials, First-principles study, Photo-decomposition, Silver nanoparticles, Surface adsorbates, Surface enhanced Raman Scattering (SERS), Theoretical calculations, Theoretical investigations
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-145587 (URN)10.1021/jp500728s (DOI)000334258600040 ()2-s2.0-84898077395 (Scopus ID)
Note

QC 20140523

Available from: 2014-05-23 Created: 2014-05-23 Last updated: 2017-12-05Bibliographically approved

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