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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Detecting Mechanochemical Atropisomerization within an STM Break Junction
AU - Leary, Edmund
AU - Roche, Cecile
AU - Jiang, Hua-Wei
AU - Grace, Iain
AU - Teresa Gonzalez, M.
AU - Rubio-Bollinger, Gabino
AU - Romero-Muniz, Carlos
AU - Xiong, Yaoyao
AU - Al-Galiby, Qusiy
AU - Noori, Mohammed
AU - Lebedeva, Maria A.
AU - Porfyrakis, Kyriakos
AU - Agrait, Nicolas
AU - Hodgson, Andrew
AU - Higgins, Simon J.
AU - Lambert, Colin J.
AU - Anderson, Harry L.
AU - Nichols, Richard J.
PY - 2018/1/17
Y1 - 2018/1/17
N2 - We have employed the scanning tunneling microscope break-junction technique to investigate the single-molecule conductance of a family of 5,15-diaryl porphyrins bearing thioacetyl (SAc) or methylsulfide (SMe) binding groups at the ortho position of the phenyl rings (S2 compounds). These ortho substituents lead to two atropisomers, cis and trans, for each compound, which do not interconvert in solution under ambient conditions; even at high temperatures, isomerization takes several hours (half-life 15 h at 140 degrees C for SAc in C2Cl4D2). All the S2 compounds exhibit two conductance groups, and comparison with a monothiolated (S1) compound shows the higher group arises from a direct Au-Porphyrin interaction. The lower conductance group is associated with the S-to-S pathway. When the binding group is SMe, the difference in junction length distribution reflects the difference in S-S distance (0.3 nm) between the two isomers. In the case of SAc, there are no significant differences between the plateau length distributions of the two isomers, and both show maximal stretching distances well exceeding their calculated junction lengths. Contact deformation accounts for part of the extra length, but the results indicate that cis-to-trans conversion takes place in the junction for the cis isomer. The barrier to atropisomerization is lower than the strength of the thiolate Au-S and.Au-Au bonds, but higher than that of the Au- SMe bond, which explains why the strain in the junction only induces isomerization in the SAc compound.
AB - We have employed the scanning tunneling microscope break-junction technique to investigate the single-molecule conductance of a family of 5,15-diaryl porphyrins bearing thioacetyl (SAc) or methylsulfide (SMe) binding groups at the ortho position of the phenyl rings (S2 compounds). These ortho substituents lead to two atropisomers, cis and trans, for each compound, which do not interconvert in solution under ambient conditions; even at high temperatures, isomerization takes several hours (half-life 15 h at 140 degrees C for SAc in C2Cl4D2). All the S2 compounds exhibit two conductance groups, and comparison with a monothiolated (S1) compound shows the higher group arises from a direct Au-Porphyrin interaction. The lower conductance group is associated with the S-to-S pathway. When the binding group is SMe, the difference in junction length distribution reflects the difference in S-S distance (0.3 nm) between the two isomers. In the case of SAc, there are no significant differences between the plateau length distributions of the two isomers, and both show maximal stretching distances well exceeding their calculated junction lengths. Contact deformation accounts for part of the extra length, but the results indicate that cis-to-trans conversion takes place in the junction for the cis isomer. The barrier to atropisomerization is lower than the strength of the thiolate Au-S and.Au-Au bonds, but higher than that of the Au- SMe bond, which explains why the strain in the junction only induces isomerization in the SAc compound.
KW - SINGLE-MOLECULE JUNCTIONS
KW - SENSITIZED SOLAR-CELLS
KW - CHARGE-TRANSPORT
KW - ELECTROMECHANICAL PROPERTIES
KW - ANCHORING GROUPS
KW - PORPHYRIN WIRES
KW - CONDUCTANCE
KW - DERIVATIVES
KW - ELECTRONICS
KW - PATHWAYS
U2 - 10.1021/jacs.7b10542
DO - 10.1021/jacs.7b10542
M3 - Journal article
VL - 140
SP - 710
EP - 718
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 2
ER -