Mechanical and Electronic Properties of Diacetylene and Polydiacetylene Self-Assembled Monolayers on Au(111)

Abstract

Polyacetylene materials, particularly two-dimensional polyacetylene thin films, have widespread applications in modern electronics and energy harvesting devices. One way to fabricate polyacetylene thin films is to attach functional groups that can covalently bond to underlying surfaces. Thiol-terminated polydiacetylenes, with their highly conjugated backbones, provide abundant possibilities to fabricate robust monolayer thin films when attached to Au surfaces. Similar to diacetylene solids or Langmuir−Blodgett films, the polymerization of diacetylene thiolates (DATs) on Au(111) surfaces can be initiated by UV radiation. The highly conjugated structures, combined with the covalent bonds to the Au surfaces, generate superior rigidity as well as distinct electronic properties as compared to typical alkanethiolate monolayers on Au substrates. Here, we explore the diacetylene thiol, HS(CH 2 ) 3 CC−CC(CH 2 ) 4 CH 3 (C3-DAT), assembled on Au(111) surfaces before and after polymerization. The monolayers were found to exhibit higher friction following polymerization due to structural changes in the films. Electronically, although I−V (dI/dV) measurements show similar spectra for both C3-DAT and C3-poly-DAT monolayer films, size-dependent differences in the electronic properties were found to arise for C3-poly-DAT islands of ca. 10−20 nm when embedded into a dodecanethiolate matrix, which can be attributed to the Coulomb blockade.

Self-Assembled Monolayers for Interfacial Engineering in Solution-Processed Thin-Film Electronic Devices: Design, Fabrication, and Applications

“…5,49,157 The last frequently selected class of head groups are those which can respond to external stimuli, such as light irradiation and chemical and biological signals. Diacetylene 152, 158 as a cross-linkable functional group, 159 can change surface properties under UV irradiation, making it capable as an auxiliary dielectric layer. In addition, photochromic groups, including azobenzenes 153−155, 160 spiropyrans 156−157, 161,162 and diarylethenes 158−159, 72,163 can reversibly change the SAM properties, including wettability, polarity, dipoles, degree of conjugation, and height, under UV and white-light irradiation.…”

Tuning Interfacial Thermal Conductance Across Metal–Organic Semiconductor Interfaces by Mixing Self-Assembled Monolayers

“…Interface engineering, as one of the most important strategies to improve electronic efficiency and functional performance, has been deeply explored in various fields such as energy harvesting, electrochemical energy storage, biomaterials, chemical sensors, biosensors, and photocatalysis. − Especially, self-assembled monolayers (SAMs) are highly ordered molecular assemblies formed spontaneously on material surfaces via chemisorption or bond that can be an excellent means of interface engineering to optimize the interface quality. The molecules of SAMs generally contain the head, tail, and terminal functional groups; it is straightforward to tune these structural characteristics to modulate the micromorphology of the interface, e.g., molecular arrangement, packing density, and uniformity.…”