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Menges JA, Clasen A, Jourdain M, Beckmann J, Hoffmann C, König J, Jung G. Surface Preparation for Single-Molecule Chemistry. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:2506-2516. [PMID: 30664351 DOI: 10.1021/acs.langmuir.8b03603] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Immobilization procedures, intended to enable prolonged observation of single molecules by fluorescence microscopy, may generate heterogeneous microenvironments, thus inducing heterogeneity in the molecular behavior. On that account, we propose a straightforward surface preparation procedure for studying chemical reactions on the single-molecule level. Sensor fluorophores were developed, which exhibit dual-emissive characteristics in a homogeneously catalyzed showcase reaction. These molecules undergo a shift of fluorescence wavelength of about 100 nm upon Pd(0)-induced deallylation in the Tsuji-Trost reaction, allowing for separate visualization of the starting material and product. Whereas a simultaneous immobilization of dye and inert silane leads to strongly polydisperse reaction kinetics, a consecutive immobilization routine with deposition of dye molecules as the last step provides substrates underlying the kinetics of ensemble experiments. Also, the found kinetics are unaffected by the chemical variation of inert silanes, nearly uniform, and therefore well reproducible. Additional parameters like photostability, signal-to-noise ratio, dye-molecule density, and spatial distribution of dye molecules are, as well, hardly affected by surface modification in the successive immobilization scheme.
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Affiliation(s)
- Johannes A Menges
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
| | - Anne Clasen
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
| | - Matthias Jourdain
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
| | - Julian Beckmann
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
| | - Caroline Hoffmann
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
| | - Julien König
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
| | - Gregor Jung
- Biophysical Chemistry , Saarland University , Building B2.2 , 66123 Saarbrücken , Germany
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Tavarone R, Charbonneau P, Stark H. Kinetic Monte Carlo simulations for birefringence relaxation of photo-switchable molecules on a surface. J Chem Phys 2016; 144:104703. [PMID: 26979700 DOI: 10.1063/1.4943393] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Recent experiments have demonstrated that in a dense monolayer of photo-switchable dye methyl-red molecules the relaxation of an initial birefringence follows a power-law decay, typical for glass-like dynamics. The slow relaxation can efficiently be controlled and accelerated by illuminating the monolayer with circularly polarized light, which induces trans-cis isomerization cycles. To elucidate the microscopic mechanism, we develop a two-dimensional molecular model in which the trans and cis isomers are represented by straight and bent needles, respectively. As in the experimental system, the needles are allowed to rotate and to form overlaps but they cannot translate. The out-of-equilibrium rotational dynamics of the needles is generated using kinetic Monte Carlo simulations. We demonstrate that, in a regime of high density and low temperature, the power-law relaxation can be traced to the formation of spatio-temporal correlations in the rotational dynamics, i.e., dynamic heterogeneity. We also show that the nearly isotropic cis isomers can prevent dynamic heterogeneity from forming in the monolayer and that the relaxation then becomes exponential.
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Affiliation(s)
- Raffaele Tavarone
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany
| | - Patrick Charbonneau
- Departments of Chemistry and Physics, Duke University, Durham, North Carolina 27708, USA
| | - Holger Stark
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany
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Zhang T, Jin C, Wang L, Yin Q. One-step synthesis of hollow polymeric nanospheres: self-assembly of amphiphilic azo polymers via hydrogen bond formation. RSC Adv 2014. [DOI: 10.1039/c4ra06415a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
We introduce a facile and novel way that describes the random amphiphilic azo copolymer to construct hollow nanospheres via hydrogen bond formation.
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Affiliation(s)
- Taoran Zhang
- Key Laboratory of Green Chemistry and Technology and College of Chemistry
- Sichuan University
- Chengdu, China
| | - Cheng Jin
- Key Laboratory of Green Chemistry and Technology and College of Chemistry
- Sichuan University
- Chengdu, China
| | - Lingyu Wang
- Key Laboratory of Green Chemistry and Technology and College of Chemistry
- Sichuan University
- Chengdu, China
| | - Qinjian Yin
- Key Laboratory of Green Chemistry and Technology and College of Chemistry
- Sichuan University
- Chengdu, China
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Martínez Hardigree JF, Dawidczyk TJ, Ireland RM, Johns GL, Jung BJ, Nyman M, Osterbacka R, Marković N, Katz HE. Reducing leakage currents in n-channel organic field-effect transistors using molecular dipole monolayers on nanoscale oxides. ACS APPLIED MATERIALS & INTERFACES 2013; 5:7025-7032. [PMID: 23845125 DOI: 10.1021/am401278p] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Leakage currents through the gate dielectric of thin film transistors remain a roadblock to the fabrication of organic field-effect transistors (OFETs) on ultrathin dielectrics. We report the first investigation of a self-assembled monolayer (SAM) dipole as an electrostatic barrier to reduce leakage currents in n-channel OFETs fabricated on a minimal, leaky ∼10 nm SiO2 dielectric on highly doped Si. The electric field associated with 1H,1H,2H,2H-perfluoro-octyltriethoxysilane (FOTS) and octyltriethoxysilane (OTS) dipolar chains affixed to the oxide surface of n-Si gave an order of magnitude decrease in gate leakage current and subthreshold leakage and a two order-of-magnitude increase in ON/OFF ratio for a naphthalenetetracarboxylic diimide (NTCDI) transistor. Identically fabricated devices on p-Si showed similarly reduced leakage and improved performance for oxides treated with the larger dipole FOTS monolayer, while OTS devices showed poorer transfer characteristics than those on bare oxide. Comparison of OFETs on both substrates revealed that relative device performance from OTS and FOTS treatments was dictated primarily by the organosilane chain and not the underlying siloxane-substrate bond. This conclusion is supported by the similar threshold voltages (VT) extrapolated for SAM-treated devices, which display positive relative VT shifts for FOTS on either substrate but opposite VT shifts for OTS treatment on n-Si and p-Si. Our results highlight the potential of dipolar SAMs as performance-enhancing layers for marginal quality dielectrics, broadening the material spectrum for low power, ultrathin organic electronics.
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Affiliation(s)
- Josué F Martínez Hardigree
- Department of Materials Science and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States
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Rastegar AJ, Vosgueritchian M, Doll JC, Mallon JR, Pruitt BL. Nanomechanical actuation of a silicon cantilever using an azo dye, self-assembled monolayer. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:7118-7124. [PMID: 23663108 DOI: 10.1021/la3034676] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The emerging fields of nanomotors and optomechanics are based on the harnessing of light to generate force. However, our ability to detect small surface stresses is limited by temperature drift, environmental noise, and low-frequency flicker electronic noise. To address these limitations, we functionalized microfabricated silicon cantilevers with an azo dye, silane-based self-assembled monolayer and modulated the surface stress by exciting the optical switch with a 405-nm laser. Atomic force microscopy, contact angle analysis, ellipsometry, and X-ray photoelectron spectroscopy verified successful assembly of molecules on the cantilever. Ultraviolet and visible spectra demonstrate optical switching of the synthesized molecule in solution. By turning the laser on and off at a specific rate (e.g., 1 Hz), the cantilever deflection can be measured via Fourier techniques, thus separating the signal of interest from the noise. This technique empowers the design of highly sensitive surface stress measurements.
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Affiliation(s)
- A Joseph Rastegar
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, USA
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Kinashi K, Kambe Y, Misaki M, Koshiba Y, Ishida K, Ueda Y. Synthesis, characterization, photo-induced alignment, and surface orientation of poly(9,9-dioctylfluorene-alt
-azobenzene)s. ACTA ACUST UNITED AC 2012. [DOI: 10.1002/pola.26338] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Shin KY, Hong JY, Lee S, Jang J. Evaluation of anti-scratch properties of graphene oxide/polypropylene nanocomposites. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c2jm15569a] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Prathap Chandran S, Mondiot F, Mondain-Monval O, Loudet JC. Photonic control of surface anchoring on solid colloids dispersed in liquid crystals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:15185-15198. [PMID: 22047168 DOI: 10.1021/la202997r] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The anchoring of liquid-crystal (LC) mesogens to the surfaces of colloids is an important factor in determining intercolloidal interactions and the symmetry of the ensuing colloidal assembly in nematic colloids. The dynamic control of surface anchoring could therefore provide a handle to tune the colloidal organization and resulting properties in these systems. In this article, we report our results on the study of thermotropic nematic LC (E7) dispersions of silica and glass microcolloids bearing photosensitive surface azobenzene groups. By the photoinduced modulation of the colloidal-LC interfacial properties, due to the trans-cis isomerization of azobenzene units, we tune the anchoring on silica colloids from homeotropic (trans-azobenzene) to homogeneous planar (cis-azobenzene) reversibly. In tune with the change in surface anchoring, the interparticle interactions were also dictated by dipolar and quadrupolar symmetries for homeotropic and homogeneous planar anchoring, respectively. In our experiments, we find that, in addition to the isomerization state of the surface-bound azobenzene units, the nature of the colloid plays a crucial role in determining the anchoring state obtained on applying photostimuli. We also study the LC anchoring on colloids as a function of the azobenzene surface density and find that beyond a threshold value the anchoring properties remain invariant.
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Affiliation(s)
- S Prathap Chandran
- University of Bordeaux, Centre de Recherche Paul Pascal-CNRS, Avenue A. Schweitzer 33600 Pessac, France.
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Fang G, Shi Y, Maclennan JE, Walba DM, Clark NA. Photodegradation of azobenzene-based self-assembled monolayers characterized by in-plane birefringence. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:10407-10411. [PMID: 21812419 DOI: 10.1021/la201306a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Azobenzene-based self-assembled monolayers (azo-SAMs) are photoactive and become orientationally ordered when illuminated with linearly polarized light (LPL), making them attractive as dynamic alignment layers in liquid crystal cells. Azo-SAMs, however, are chemically unstable when exposed to both air and light. We have characterized the photodegradation of a methyl red-based SAM by measuring with a high-sensitivity polarimeter the optical anisotropy induced by illumination with linearly polarized actinic light after the sample is irradiated with circularly polarized light (CPL) in air. The number of unbleached, photoactive molecules in the SAM decays exponentially with CPL exposure time, lowering the reorientation rate during photowriting with LPL. Azo-SAMs in an argon atmosphere, in contrast, are chemically stable and remain photoactive even after exposure to CPL.
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Affiliation(s)
- Guanjiu Fang
- Departments of Physics, University of Colorado, Boulder, Colorado 80309, USA
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