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Title: Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties

Here, three oligothiophene (terthiophene, tetrathiophene and pentathiophene) derivatives are synthesized and their monolayer self-assemblies on gold (Au) are prepared via Au–S covalent bond. Our UV–Vis experimental characterization of solution reveals the dependence of the optical properties on the conjugation length of the oligothiophenes, which compares well with Time-Dependent Density Functional Theory (TDDFT) simulations of spectra of individual chromophores. Photoluminescent spectra of thin films show pronounced red shifts compared to that of solutions, suggesting strong inter-oligomer interactions. The comparative studies of cyclic voltammograms of tetrathiophene from solution, cast film and self-assembled monolayer (SAM) indicate presence of one, two, and three oxidized species in these samples, respectively, suggesting a very strong electronic coupling between tetrathiophene molecules in the SAM. Scanning tunneling microscopy (STM) imaging of SAMs of the tetrathiophene on an atomically flat Au surface exhibits formation of monolayer assemblies with molecular order, and the molecular packing appears to show an overlay of oligothiophene molecules on top of another one. In contrast, the trimer and pentamer images show only aggregated species lacking long-range order on the molecular level. Such trends in going from disordered–ordered–disordered monolayer assemblies are mainly due to a delicate balance between inter-chromophore π–π couplings, hydrophobic interaction and the propensitymore » to form Au–S covalent bond. Such hypothesis has been validated by our computational results suggesting different interaction patterns of oligothiophenes with odd numbered and even numbered thiophene repeat units placed in a dimer configuration. Finally, observed correlations between oligomer geometry and structural order of monolayer assembly elucidate important structure–property relationships and have implications for these molecular structures in organic optoelectronic devices and energy devices.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-17-27858
Journal ID: ISSN 0301-0104
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Chemical Physics
Additional Journal Information:
Journal Volume: 481; Journal ID: ISSN 0301-0104
Publisher:
Elsevier
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA); LANL Laboratory Directed Research and Development (LDRD) Program
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 74 ATOMIC AND MOLECULAR PHYSICS; oligothiophene; self-assembly; spectroscopy; structural order; TDDFT
OSTI Identifier:
1477679

Kuo, Cheng -Yu, Liu, Yinghao, Yarotski, Dmitry, Li, Hao, Xu, Ping, Yen, Hung-Ju, Tretiak, Sergei, and Wang, Hsing -Lin. Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties. United States: N. p., Web. doi:10.1016/j.chemphys.2016.05.015.
Kuo, Cheng -Yu, Liu, Yinghao, Yarotski, Dmitry, Li, Hao, Xu, Ping, Yen, Hung-Ju, Tretiak, Sergei, & Wang, Hsing -Lin. Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties. United States. doi:10.1016/j.chemphys.2016.05.015.
Kuo, Cheng -Yu, Liu, Yinghao, Yarotski, Dmitry, Li, Hao, Xu, Ping, Yen, Hung-Ju, Tretiak, Sergei, and Wang, Hsing -Lin. 2016. "Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties". United States. doi:10.1016/j.chemphys.2016.05.015. https://www.osti.gov/servlets/purl/1477679.
@article{osti_1477679,
title = {Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties},
author = {Kuo, Cheng -Yu and Liu, Yinghao and Yarotski, Dmitry and Li, Hao and Xu, Ping and Yen, Hung-Ju and Tretiak, Sergei and Wang, Hsing -Lin},
abstractNote = {Here, three oligothiophene (terthiophene, tetrathiophene and pentathiophene) derivatives are synthesized and their monolayer self-assemblies on gold (Au) are prepared via Au–S covalent bond. Our UV–Vis experimental characterization of solution reveals the dependence of the optical properties on the conjugation length of the oligothiophenes, which compares well with Time-Dependent Density Functional Theory (TDDFT) simulations of spectra of individual chromophores. Photoluminescent spectra of thin films show pronounced red shifts compared to that of solutions, suggesting strong inter-oligomer interactions. The comparative studies of cyclic voltammograms of tetrathiophene from solution, cast film and self-assembled monolayer (SAM) indicate presence of one, two, and three oxidized species in these samples, respectively, suggesting a very strong electronic coupling between tetrathiophene molecules in the SAM. Scanning tunneling microscopy (STM) imaging of SAMs of the tetrathiophene on an atomically flat Au surface exhibits formation of monolayer assemblies with molecular order, and the molecular packing appears to show an overlay of oligothiophene molecules on top of another one. In contrast, the trimer and pentamer images show only aggregated species lacking long-range order on the molecular level. Such trends in going from disordered–ordered–disordered monolayer assemblies are mainly due to a delicate balance between inter-chromophore π–π couplings, hydrophobic interaction and the propensity to form Au–S covalent bond. Such hypothesis has been validated by our computational results suggesting different interaction patterns of oligothiophenes with odd numbered and even numbered thiophene repeat units placed in a dimer configuration. Finally, observed correlations between oligomer geometry and structural order of monolayer assembly elucidate important structure–property relationships and have implications for these molecular structures in organic optoelectronic devices and energy devices.},
doi = {10.1016/j.chemphys.2016.05.015},
journal = {Chemical Physics},
number = ,
volume = 481,
place = {United States},
year = {2016},
month = {6}
}