pH control of conductance in a pyrazolyl Langmuir-Blodgett monolayer

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2021-03, Vol.9 (8), p.2882-2889
• Main Authors: Herrer, L, Martín, S, González-Orive, A, Milan, D. C, Vezzoli, A, Nichols, R. J, Serrano, J. L, Cea, P
• Format: Article
• Language: English
• Subjects: Benzene; Coupling (molecular); Electrical junctions; Electrical properties; Gold; Langmuir-Blodgett films; Molecular structure; Monolayers; pH control; Pyrazole; Resistance; Self-assembly; Substrates
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d0tc05658h

In this contribution, pyrazole is identified as an excellent anchoring group capable of forming well-ordered Langmuir-Blodgett (LB) monolayers onto gold substrates. In contrast, the formation of self-assembled (SA) monolayers is prevented due to the extraction of gold atoms from the surface upon the incubation process required for the formation of these films. The electronic coupling strength of pyrazole-gold junctions is explored through evaluation of the electrical properties of LB films incorporating a double pyrazole terminated molecular wire, namely 1,4-bis(1 H -pyrazol-4-ylethynyl)benzene, 1 ; these electrical properties are compared with those of molecules having a similar chemical structure, geometry and length. The conductance value for LB films of 1 is high when the monolayer is transferred from a Langmuir film prepared onto a basic subphase, 1.19 × 10 −4 G 0 , as it is more than four times larger than the conductance of the same compound incorporated on a LB film prepared from a water subphase, 0.27 × 10 −4 G 0 . These results are interpreted in terms of the deprotonation of the pyrazole group in a basic media that leads to the formation of the pyrazolate (deprotonated pyrazole) moiety. This results in a more efficient electronic coupling with the gold tip of the scanning tunnelling microscope used for film characterization. In this contribution pyrazole is identified as an excellent anchor group that forms high quality films under pH controlled conditions, allowing the modulation of the electrical properties with a more efficient electronic coupling in basic conditions.