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Title: Tunneling across SAMs Containing Oligophenyl Groups

Abstract

This paper reports rates of charge tunneling across self-assembled monolayers (SAMs) of compounds containing oligophenyl groups, supported on gold and silver, using Ga 2O 3/EGaIn as the top electrode. It compares the attenuation constant, $β$, and the pre-exponential parameter, $$J_0$$, of the simplified Simmons equation across oligophenyl groups (R = Ph n; n = 1, 2, 3) with three different anchoring groups (thiol, HSR; methanethiol, HSCH 2R; and acetylene, HC≡CR) that attach R to the template-stripped gold or silver substrate. The results demonstrate that the structure of the molecular linker between the anchoring group (-S- or -C≡C-) and the oligophenyl moiety significantly influences the rate of charge transport. SAMs of SPh n and C≡CPh n on gold show similar values of $β$ and log $$|J_0|$$ ($β$ = 0.28 ± 0.03 Å$$^{–1}$$ and log $$|J_0|$$ = 2.7 ± 0.1 for Au/SPhn; $β$ = 0.30 ± 0.02 $$Å^{–1}$$ and log $$|J_0|$$ = 3.0 ± 0.1 for Au/C≡CPh n). The introduction of a single intervening methylene (CH 2) group between the anchoring sulfur atom and the aromatic units generates SAMs of SCH2Phn and increases $β$ to ca. 0.66 ± 0.06 $$Å^{–1}$$ on both gold and silver substrates. (For n-alkanethiolates on gold, the corresponding values are $β$ = 0.76 ± 0.03 $$Å^{–1}$$ and log $|J)0|$ = 4.2 ± 0.2). Density functional theory calculations indicate that the highest occupied molecular orbitals (HOMOs) of both SPh n and C≡CPh n extend beyond the anchoring group and onto the phenyl rings; SAMs composed of these two groups of molecules result in indistinguishable rates of charge transport. The introduction of the CH 2 group, to generate SCH 2Ph n, disrupts the delocalization of the orbitals, localizes the HOMO on the anchoring sulfur atom, and results in the experimentally observed increase in $β$ to a value closer to that of a SAM of n-alkylthiolate molecules.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [2];  [2];  [1];  [1]
  1. Harvard Univ., Cambridge, MA (United States). Dept. of Chemistry and Chemical Biology
  2. Jagiellonian Univ., Krakow (Poland)
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Bio-Inspired Energy Science (CBES)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1387947
Grant/Contract Number:  
SC0000989
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 120; Journal Issue: 21; Related Information: CBES partners with Northwestern University (lead); Harvard University; New York University; Pennsylvania State University; University of Michigan; University of Pittsburgh; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (homogeneous); solar (photovoltaic); bio-inspired; charge transport; mesostructured materials; materials and chemistry by design; synthesis (novel materials); synthesis (self-assembly)

Citation Formats

Bowers, Carleen M., Rappoport, Dmitrij, Baghbanzadeh, Mostafa, Simeone, Felice C., Liao, Kung-Ching, Semenov, Sergey N., Żaba, Tomasz, Cyganik, Piotr, Aspuru-Guzik, Alan, and Whitesides, George M. Tunneling across SAMs Containing Oligophenyl Groups. United States: N. p., 2016. Web. doi:10.1021/acs.jpcc.6b01253.
Bowers, Carleen M., Rappoport, Dmitrij, Baghbanzadeh, Mostafa, Simeone, Felice C., Liao, Kung-Ching, Semenov, Sergey N., Żaba, Tomasz, Cyganik, Piotr, Aspuru-Guzik, Alan, & Whitesides, George M. Tunneling across SAMs Containing Oligophenyl Groups. United States. doi:10.1021/acs.jpcc.6b01253.
Bowers, Carleen M., Rappoport, Dmitrij, Baghbanzadeh, Mostafa, Simeone, Felice C., Liao, Kung-Ching, Semenov, Sergey N., Żaba, Tomasz, Cyganik, Piotr, Aspuru-Guzik, Alan, and Whitesides, George M. Mon . "Tunneling across SAMs Containing Oligophenyl Groups". United States. doi:10.1021/acs.jpcc.6b01253. https://www.osti.gov/servlets/purl/1387947.
@article{osti_1387947,
title = {Tunneling across SAMs Containing Oligophenyl Groups},
author = {Bowers, Carleen M. and Rappoport, Dmitrij and Baghbanzadeh, Mostafa and Simeone, Felice C. and Liao, Kung-Ching and Semenov, Sergey N. and Żaba, Tomasz and Cyganik, Piotr and Aspuru-Guzik, Alan and Whitesides, George M.},
abstractNote = {This paper reports rates of charge tunneling across self-assembled monolayers (SAMs) of compounds containing oligophenyl groups, supported on gold and silver, using Ga2O3/EGaIn as the top electrode. It compares the attenuation constant, $β$, and the pre-exponential parameter, $J_0$, of the simplified Simmons equation across oligophenyl groups (R = Phn; n = 1, 2, 3) with three different anchoring groups (thiol, HSR; methanethiol, HSCH2R; and acetylene, HC≡CR) that attach R to the template-stripped gold or silver substrate. The results demonstrate that the structure of the molecular linker between the anchoring group (-S- or -C≡C-) and the oligophenyl moiety significantly influences the rate of charge transport. SAMs of SPhn and C≡CPhn on gold show similar values of $β$ and log $|J_0|$ ($β$ = 0.28 ± 0.03 Å$^{–1}$ and log $|J_0|$ = 2.7 ± 0.1 for Au/SPhn; $β$ = 0.30 ± 0.02 $Å^{–1}$ and log $|J_0|$ = 3.0 ± 0.1 for Au/C≡CPhn). The introduction of a single intervening methylene (CH2) group between the anchoring sulfur atom and the aromatic units generates SAMs of SCH2Phn and increases $β$ to ca. 0.66 ± 0.06 $Å^{–1}$ on both gold and silver substrates. (For n-alkanethiolates on gold, the corresponding values are $β$ = 0.76 ± 0.03 $Å^{–1}$ and log $|J)0|$ = 4.2 ± 0.2). Density functional theory calculations indicate that the highest occupied molecular orbitals (HOMOs) of both SPhn and C≡CPhn extend beyond the anchoring group and onto the phenyl rings; SAMs composed of these two groups of molecules result in indistinguishable rates of charge transport. The introduction of the CH2 group, to generate SCH2Phn, disrupts the delocalization of the orbitals, localizes the HOMO on the anchoring sulfur atom, and results in the experimentally observed increase in $β$ to a value closer to that of a SAM of n-alkylthiolate molecules.},
doi = {10.1021/acs.jpcc.6b01253},
journal = {Journal of Physical Chemistry. C},
issn = {1932-7447},
number = 21,
volume = 120,
place = {United States},
year = {2016},
month = {4}
}

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