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Riaz S, Friedrichs G. Vibrational sum-frequency generation study of molecular structure, sterical constraints and nonlinear optical switching contrast of mixed alkyl-azobenzene self-assembled monolayers. Z PHYS CHEM 2020. [DOI: 10.1515/zpch-2020-1655] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Abstract
Self-assembled monolayers (SAMs) of azobenzene (AB) functionalized alkyl thiols on gold diluted with simple alkyl thiols provide a straightforward way to photochromic surfaces with high and tunable photoswitching efficiency. Trans-cis isomerization of the AB molecule changes the physical properties of the surface, including the nonlinear optical (NLO) response. Vibrational sum-frequency generation (VSFG) spectroscopy as a nonlinear type of laser spectroscopy offers surface- and orientation-sensitive insight into the molecular structure of mixed SAMs. In this study, VSFG as well as ultraviolet-visible (UV/Vis) spectroscopy has been employed to investigate the morphology, molecular structure, and NLO response of mixed SAMs with systematically varied surface composition. Methylazobenzene (MeAB) has been used as the molecular switch with the methyl substituent serving as orientational VSFG marker. Both short-chain and long-chain alkyl thiol co-ligands have been used to gain insight into the interplay between SAM structure and sterical constraints that are known to limit the free switching volume. Underlining the dominating role of sterical effects for controlling photochromic properties, a strong inhibition of the photoswitching efficiency and NLO response has been observed for the SAMs with an alkyl thiol co-ligand long enough to spatially extend into the layer of the MeAB chromophore. Overall, with <12% signal change, the relative NLO switching contrasts remained low in all cases. VSFG spectral trends clearly revealed that the presumably higher photoswitching efficiency upon dilution with the co-ligand is counteracted by a loss of structural order of the chromophore.
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Affiliation(s)
- Saira Riaz
- Islamabad College for Girls , F-6/2 , Islamabad, 44000 , Pakistan
| | - Gernot Friedrichs
- Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel , Max-Eyth-Str. 1, 24118 , Kiel , Germany
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2
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Kunfi A, Bernadett Vlocskó R, Keresztes Z, Mohai M, Bertóti I, Ábrahám Á, Kiss É, London G. Photoswitchable Macroscopic Solid Surfaces Based On Azobenzene-Functionalized Polydopamine/Gold Nanoparticle Composite Materials: Formation, Isomerization and Ligand Exchange. Chempluschem 2020; 85:797-805. [PMID: 31967410 DOI: 10.1002/cplu.201900674] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Revised: 01/07/2020] [Indexed: 12/21/2022]
Abstract
The facile preparation of dynamic interfaces is presented based on the combination of photoisomerizable azobenzenes and polydopamine (PDA)/Au nanoparticle composite materials. Azobenzenes with different spacer lengths (C3 , C6 ) and surface-binding groups (SH, NH2 ) were synthesized. The polymer layer on macroscopic quartz surface was prepared by the facile aerobic autopolymerisation of dopamine hydrochloride under basic conditions. The presence of redox-active catechol moieties meant that gold nanoparticles were formed on the polymer surface. The obtained UV-Vis spectroscopic results confirmed that following their successful assembly, the switching of azobenzenes on PDA/Au was not affected by the surface binding group and the spacer length of the azobenzene molecules under the measurement conditions. Furthermore, facilitated by the curved nature of the Au particles, the surface-bound azobenzene layer could be reconstructed by ligand-exchange processes, and the photochemical characterization of the mixed layer was performed.
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Affiliation(s)
- Attila Kunfi
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary.,Department of Organic Chemistry, University of Szeged, Dóm tér 8, 6720, Szeged, Hungary
| | - Rita Bernadett Vlocskó
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary
| | - Zsófia Keresztes
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary
| | - Miklós Mohai
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary
| | - Imre Bertóti
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary
| | - Ágnes Ábrahám
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary.,Laboratory of Interfaces and Nanostructures, Eötvös Loránd University, Pázmány Péter stny. 1/A, 1117, Budapest, Hungary
| | - Éva Kiss
- Laboratory of Interfaces and Nanostructures, Eötvös Loránd University, Pázmány Péter stny. 1/A, 1117, Budapest, Hungary
| | - Gábor London
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2., 1117, Budapest, Hungary
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3
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Schuster S, Füser M, Asyuda A, Cyganik P, Terfort A, Zharnikov M. Photoisomerization of azobenzene-substituted alkanethiolates on Au(111) substrates in the context of work function variation: the effect of structure and packing density. Phys Chem Chem Phys 2019; 21:9098-9105. [PMID: 31017144 DOI: 10.1039/c9cp00255c] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Photoisomerization of a series of custom-designed, azobenzene-substituted alkanethiolate (AT) self-assembled monolayers (SAMs) on Au(111) substrates was studied in the context of work function variation, using Kelvin probe measurements as a transduction technique. These SAMs featured variable packing density (by ∼14%; due to the odd-even effects) and, as an option, were additionally decorated with the electron donating/withdrawing -CH3 and -CF3 tail group, respectively, which induce additional dipole moments. The efficiency of photoisomerization and the respective extent of work function variation (ΔΦ) were found to be quite low and independent of the packing density in the SAMs, within the given odd-even packing density variation. They could only be increased, up to ca. 40 meV for ΔΦ, by mixing the azobenzene-substituted ATs with shorter "matrix" molecules, which were introduced for a partial release of the sterical constraints. The ΔΦ values for the SAMs decorated with the -CH3 and -CF3 tail groups were found to be lower than those for the monolayers without such a decoration, which correlated well with the theoretical estimates for the change of the dipole moment of the relevant molecules upon the photoisomerization.
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Affiliation(s)
- Swen Schuster
- Angewandte Physikalische Chemie, Universität Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.
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Cho D, Yang M, Shin N, Hong S. Mapping reversible photoswitching of molecular resistance fluctuations during the conformational transformation of azobenzene-terminated molecular switches. NANOTECHNOLOGY 2018; 29:365704. [PMID: 29877868 DOI: 10.1088/1361-6528/aacb17] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We report a direct mapping and analysis of electrical noise in azobenzene-terminated molecular monolayers, revealing reversible photoswitching of the molecular resistance fluctuations in the layers. In this work, a conducting atomic force microscope combined with a homemade spectrum analyzer was used to image electrical current and noise at patterned self-assembled monolayers (SAMs) of azobenzene-terminated molecular wires on a gold substrate. We analyzed the current and noise imaging data to obtain maps of molecular resistances and amount of mean-square fluctuations in the resistances of the regions of trans-azobenzene and a cis/trans-azobenzene mixture. We revealed that the fluctuations in the molecular resistances in the SAMs were enhanced after the trans-to-cis isomerization, while the resistances were reduced. This result could be attributed to enhanced disorders in the molecular arrangements in the cis-SAMs. Furthermore, we observed that the changes in the resistance fluctuations were reversible with respect to repeated trans-to-cis and cis-to-trans isomerizations, indicating that the effects originated from reversible photoswitching of the molecular structures rather than irreversible damages of the molecules. These findings provide valuable insights into the electrical fluctuations in photoswitchable molecules, which could be utilized in further studies on molecular switches and molecular electronics in general.
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Affiliation(s)
- Duckhyung Cho
- Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Republic of Korea
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5
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Tuca E, Paci I. Computer simulations of self-assembled energy materials. MOLECULAR SIMULATION 2017. [DOI: 10.1080/08927022.2017.1306063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- E. Tuca
- Department of Chemistry, University of Victoria, Victoria, Canada
| | - I. Paci
- Department of Chemistry, University of Victoria, Victoria, Canada
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6
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Moldt T, Przyrembel D, Schulze M, Bronsch W, Boie L, Brete D, Gahl C, Klajn R, Tegeder P, Weinelt M. Differing Isomerization Kinetics of Azobenzene-Functionalized Self-Assembled Monolayers in Ambient Air and in Vacuum. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:10795-10801. [PMID: 27681851 DOI: 10.1021/acs.langmuir.6b01690] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Azobenzenealkanethiols in self-assembled monolayers (SAMs) on Au(111) exhibit reversible trans-cis photoisomerization when diluted with alkanethiol spacers. Using these mixed SAMs, we show switching of the linear optical and second-harmonic response. The effective switching of these surface optical properties relies on a reasonably large cross section and a high photoisomerization yield as well as a long lifetime of the metastable cis isomer. We quantified the switching process by X-ray absorption spectroscopy. The cross sections for the trans-cis and cis-trans photoisomerization with 365 and 455 nm light, respectively, are 1 order of magnitude smaller than in solution. In vacuum, the 365 nm photostationary state comprises 50-74% of the molecules in the cis form, limited by their rapid thermal isomerization back to the trans state. In contrast, the 455 nm photostationary state contains nearly 100% trans-azobenzene. We determined time constants for the thermal cis-trans isomerization of only a few minutes in vacuum and in a dry nitrogen atmosphere but of more than 1 day in ambient air. Our results suggest that adventitious water adsorbed on the surface of the SAM stabilizes the polar cis configuration of azobenzene under ambient conditions. The back reaction rate constants differing by 2 orders of magnitude underline the huge influence of the environment and, accordingly, its importance when comparing various experiments.
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Affiliation(s)
- Thomas Moldt
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
| | - Daniel Przyrembel
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
| | - Michael Schulze
- Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg , 69120 Heidelberg, Germany
| | - Wibke Bronsch
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
| | - Larissa Boie
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
| | - Daniel Brete
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
| | - Cornelius Gahl
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
| | - Rafal Klajn
- Department of Organic Chemistry, Weizmann Institute of Science , 76100 Rehovot, Israel
| | - Petra Tegeder
- Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg , 69120 Heidelberg, Germany
| | - Martin Weinelt
- Fachbereich Physik, Freie Universität Berlin , 14195 Berlin, Germany
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7
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Köhntopp A, Dittner M, Temps F. Femtosecond Time-Resolved Dynamics of trans-Azobenzene on Gold Nanoparticles. J Phys Chem Lett 2016; 7:1088-1095. [PMID: 26959865 DOI: 10.1021/acs.jpclett.6b00102] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report a first femtosecond time-resolved transient absorption study of the photoinduced ultrafast dynamics of trans-azobenzene (AB) on gold nanoparticles (AuNPs). The observed changes in optical density following excitation at λ = 357 nm were analyzed by using temperature-dependent Mie theory and by Lorentzian band fitting to disentangle the ultrafast relaxation of the local surface plasmon resonance (LSPR) excitation of the Au core and the electronic deactivation of the attached AB ligands. The analysis of the dynamics associated with the AB photochrome yielded lifetime constants of τ1 = 1.2 ± 0.2 ps and τ2 = 4.7 ± 1.1 ps. Both values together indicate surprisingly little difference in the dynamics of the AB ligand on the AuNPs vs in solution. Our results thus highlight the extraordinarily efficient electronic decoupling of the azo chromophore and the Au core by the alkyl linker chain.
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Affiliation(s)
- Anja Köhntopp
- Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel , Olshausenstraße 40, D-24098 Kiel, Germany
| | - Mark Dittner
- Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel , Olshausenstraße 40, D-24098 Kiel, Germany
| | - Friedrich Temps
- Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel , Olshausenstraße 40, D-24098 Kiel, Germany
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8
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Tuca E, Paci I. Fundamental aspects in surface self-assembly: theoretical implications of molecular polarity and shape. Phys Chem Chem Phys 2016; 18:6498-508. [PMID: 26864632 DOI: 10.1039/c5cp04479k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
We investigate fundamental aspects of structure formation in molecular self-assembly, by examining the emergence of order upon adsorption of a series of model molecules. It is known that strongly polar diatomic molecules form three-dimensional crystals in the absence of a substrate. This tendency can be disrupted upon assembly on a solid surface, and various other types of order may arise. Depending on the relative strength of the interactions, disordered phases, two-dimensional crystals commensurate to the surface, and unmodified crystals were observed upon adsorption of simple dipoles in the present work. Introduction of steric features, in the form of a longer backbone or substituents external to the polar pair, led to even richer phase diagrams. The formation of two-dimensional phases with nematic (parallel) or antiparallel alignment was accomplished by altering the polarity of the end groups on needle-like molecules, whereas embedded charged groups made two-dimensional structure unstable for even very long molecules. These molecules preferred to align in long, often desorbed, molecular wires. The wealth of phases observed here parallel the results of experimental systematic or incidental studies of the relationships between molecular interactions and self-assembled patterns, and provide some insight into the molecular handles that self-assembly researchers can wield to guide the process towards a desired structural outcome.
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Affiliation(s)
- Emilian Tuca
- Department of Chemistry and the Centre for Advanced Materials and Related Technology, University of Victoria, Victoria, BC V8W 3V6, Canada.
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9
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Moldt T, Brete D, Przyrembel D, Das S, Goldman JR, Kundu PK, Gahl C, Klajn R, Weinelt M. Tailoring the properties of surface-immobilized azobenzenes by monolayer dilution and surface curvature. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:1048-57. [PMID: 25544061 DOI: 10.1021/la504291n] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Photoswitching in densely packed azobenzene self-assembled monolayers (SAMs) is strongly affected by steric constraints and excitonic coupling between neighboring chromophores. Therefore, control of the chromophore density is essential for enhancing and manipulating the photoisomerization yield. We systematically compare two methods to achieve this goal: First, we assemble monocomponent azobenzene-alkanethiolate SAMs on gold nanoparticles of varying size. Second, we form mixed SAMs of azobenzene-alkanethiolates and "dummy" alkanethiolates on planar substrates. Both methods lead to a gradual decrease of the chromophore density and enable efficient photoswitching with low-power light sources. X-ray spectroscopy reveals that coadsorption from solution yields mixtures with tunable composition. The orientation of the chromophores with respect to the surface normal changes from a tilted to an upright position with increasing azobenzene density. For both systems, optical spectroscopy reveals a pronounced excitonic shift that increases with the chromophore density. In spite of exciting the optical transition of the monomer, the main spectral change in mixed SAMs occurs in the excitonic band. In addition, the photoisomerization yield decreases only slightly by increasing the azobenzene-alkanethiolate density, and we observed photoswitching even with minor dilutions. Unlike in solution, azobenzene in the planar SAM can be switched back almost completely by optical excitation from the cis to the original trans state within a short time scale. These observations indicate cooperativity in the photoswitching process of mixed SAMs.
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Affiliation(s)
- Thomas Moldt
- Fachbereich Physik, Freie Universität Berlin , Arnimallee 14, 14195 Berlin, Germany
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10
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Müller M, Jung U, Gusak V, Ulrich S, Holz M, Herges R, Langhammer C, Magnussen O. Localized surface plasmon resonance investigations of photoswitching in azobenzene-functionalized self-assembled monolayers on Au. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:10693-10699. [PMID: 23909478 DOI: 10.1021/la401825f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Localized plasmon resonance (LSPR) spectroscopy, employing gold nanodisk substrates, is applied for studies of photoswitching in self-assembled monolayers of azobenzene-containing thiols. By choosing customized samples in which the sharp LSPR resonance is well separated from the spectral regime of the molecular absorption bands, the photoisomerization kinetics of the adlayer can be monitored in real time. Quantitative data on the photoinduced trans-cis and cis-trans isomerization processes in inert gas atmosphere were obtained as a function of irradiation intensity and temperature, demonstrating the high sensitivity of this technique to such processes in functional adlayers.
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Affiliation(s)
- Mathias Müller
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Leibnizstraße 19, 24118 Kiel, Germany
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11
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Claridge SA, Liao WS, Thomas JC, Zhao Y, Cao H, Cheunkar S, Serino AC, Andrews AM, Weiss PS. From the bottom up: dimensional control and characterization in molecular monolayers. Chem Soc Rev 2013; 42:2725-45. [PMID: 23258565 PMCID: PMC3596502 DOI: 10.1039/c2cs35365b] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Self-assembled monolayers are a unique class of nanostructured materials, with properties determined by their molecular lattice structures, as well as the interfaces with their substrates and environments. As with other nanostructured materials, defects and dimensionality play important roles in the physical, chemical, and biological properties of the monolayers. In this review, we discuss monolayer structures ranging from surfaces (two-dimensional) down to single molecules (zero-dimensional), with a focus on applications of each type of structure, and on techniques that enable characterization of monolayer physical properties down to the single-molecule scale.
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Affiliation(s)
- Shelley A. Claridge
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Wei-Ssu Liao
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - John C. Thomas
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Yuxi Zhao
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Huan Cao
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Sarawut Cheunkar
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Andrew C. Serino
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Anne M. Andrews
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Psychiatry, University of California, Los Angeles, Los Angeles, California 90095, United States
- Semel Institute for Neuroscience & Human Behavior, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Paul S. Weiss
- California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
- Department of Materials Science & Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
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Katano S, Kim Y, Kitagawa T, Kawai M. Tailoring electronic states of a single molecule using adamantane-based molecular tripods. Phys Chem Chem Phys 2013; 15:14229-33. [PMID: 23877197 DOI: 10.1039/c3cp51612a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Satoshi Katano
- Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
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