A comprehensive study of extended tetrathiafulvalene cruciform molecules for molecular electronics: synthesis and electrical transport measurements.
Cruciform-like molecules with two orthogonally placed π-conjugated systems have in recent years attracted significant interest for their potential use as molecular wires in molecular electronics. Here we present synthetic protocols for a large selection of cruciform molecules based on oligo(phenyleneethynylene) (OPE) and tetrathiafulvalene (TTF) scaffolds, end-capped with acetyl-protected thiolates as electrode anchoring groups. The molecules were subjected to a comprehensive study of their conducting properties as well as their photophysical and electrochemical properties in solution. The complex nature of the molecules and their possible binding in different configurations in junctions called for different techniques of conductance measurements: (1) conducting-probe atomic force microscopy (CP-AFM) measurements on self-assembled monolayers (SAMs), (2) mechanically controlled break-junction (MCBJ) measurements, and (3) scanning tunneling microscopy break-junction (STM-BJ) measurements. The CP-AFM measurements showed structure-property relationships from SAMs of series of OPE3 and OPE5 cruciform molecules; the conductance of the SAM increased with the number of dithiafulvene (DTF) units (0, 1, 2) along the wire, and it increased when substituting two arylethynyl end groups of the OPE3 backbone with two DTF units. The MCBJ and STM-BJ studies on single molecules both showed that DTFs decreased the junction formation probability, but, in contrast, no significant influence on the single-molecule conductance was observed. We suggest that the origins of the difference between SAM and single-molecule measurements lie in the nature of the molecule-electrode interface as well as in effects arising from molecular packing in the SAMs. This comprehensive study shows that for complex molecules care should be taken when directly comparing single-molecule measurements and measurements of SAMs and solid-state devices thereof.
Department of Chemistry & Center for Exploitation of Solar Energy & Nano-Science Center & Danish-Chinese Center for Nano-Electronics, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
Christian R
CR
Parker
Edmund
E
Leary
Riccardo
R
Frisenda
Zhongming
Z
Wei
Karsten S
KS
Jennum
Emil
E
Glibstrup
Peter Bæch
PB
Abrahamsen
Marco
M
Santella
Mikkel A
MA
Christensen
Eduardo Antonio
EA
Della Pia
Tao
T
Li
Maria Teresa
MT
Gonzalez
Xingbin
X
Jiang
Thorbjørn J
TJ
Morsing
Gabino
G
Rubio-Bollinger
Bo W
BW
Laursen
Kasper
K
Nørgaard
Herre
H
van der Zant
Nicolas
N
Agrait
Mogens Brøndsted
MB
Nielsen