Effects of Alkyl Chain Length and Hydrogen Bonds on the Cooperative Self‐Assembly of 2‐Thienyl‐Type Diarylethenes at a Liquid/Highly Oriented Pyrolytic Graphite (HOPG) Interface

Abstract

An appropriate understanding of the process of self-assembly is of critical importance to tailor nanostructured order on 2D surfaces with functional molecules. Photochromic compounds are promising candidates for building blocks of advanced photoresponsive surfaces. To investigate the relationship between molecular structure and the mechanism of ordering formation, 2-thienyl-type diarylethenes with various lengths of alkyl side chains linked through an amide or ester group were synthesized. Their self-assemblies at a liquid/solid interface were investigated by scanning tunneling microscopy (STM). The concentration dependence of the surface coverage was analyzed by using a cooperative model for a 2D surface based on two characteristic parameters: the nucleation equilibrium constant (Kn) and the elongation equilibrium constant (Ke). The following conclusions can be drawn. 1) The concentration at which a stable 2D molecular ordering is observed by STM exponentially decreases with increasing length of the alkyl chain. 2) Compounds bearing amide groups have higher degrees of cooperativity in self-assembly on 2D surfaces (i.e., σ, which is defined as Kn/Ke) than compounds with ester groups. 3) The self-assembly process of the open-ring isomer of an ester derivative is close to isodesmic, whereas that of the closed-ring isomer is cooperative because of the difference in equilibrium constants for the nucleation step (i.e., Kn) between the two isomers.

An STM Investigation on a Metal Induced Structural Evolution of an m-Substituted Bipyridine Derivative on Highly Oriented Pyrolytic Graphite

“…Similar phenomena have also been observed in arrays of other alkane derivatives, in which the alkyl chains take different angles to fulfill the formation of hydrogen bonds. [9,[33][34][35][36] In addition, the packing patterns of m-substituted 9-bpy and 14-bpy are similar to that of p-substituted bpy reported by De feyter et al, [26,27] except for only one type of adsorption structure was observed for 9-bpy and 14-bpy arrays. This may be due to the different structural symmetry of m-and p-substituted bpys.…”

Photochromic Diarylethenes Designed for Surface Deposition: From Self‐Assembled Monolayers to Single Molecules

“…In this particular section of our present review, we focus on diarylethenes and how functionalities attached to their switching units affect the assembly/disassembly process in the solid/liquid interface. This section therefore aims to draw molecular design principles for surface assembly formation based on the particular geometry and photochemistry of diarylethenes on the solid/liquid interface, as such processes can give insight to surface‐molecule interactions …”

“…By looking at the concentration dependence of surface coverage, Matsuda et al . remarked that the nucleation process for 9 c assemblies was more thermodynamically favorable than that of the o form …”

“…This section therefore aims to draw molecular design principles for surface assembly formation based on the particular geometry and photochemistry of diarylethenes on the solid/liquid interface, as such processes can give insight to surface-molecule interactions. [49,69] Diarylethenes are promising for molecular electronics due to their bistable isomerization. For such applications, the effects of such interconversion on molecule-molecule and surfacemolecule interactions on a 2D solid surface are important.…”

“…[67] They further studied other diarylethene derivatives. (6-11, Scheme 3) [68][69][70][71] From a survey of these studies, general molecular design principles could be drawn to come up with an idea of what functional groups aid in the formation of assemblies. Compound 6 has amide groups capable of hydrogen bonding; 7 has extra methyl groups; 8 has no amide groups.…”