Journal
LANGMUIR
Volume 33, Issue 43, Pages 12453-12462Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.langmuir.7b03007
Keywords
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Funding
- JSPS KAKENHI [2435004, 15H02164]
- National Science Foundation CHE [16-10328]
- Grants-in-Aid for Scientific Research [15H02164] Funding Source: KAKEN
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We present here hexagonal tiling using hexagonal phenylene-ethynylene and phenylene-butadiynylene macrocycles attached by alkyl ester groups, PEM-C6 and PBM-C8, respectively, or triethylene glycol ester groups, PEM-TEG and PBM-TEG, respectively, at each vertex of the macrocyclic periphery at the liquid/solid interface. In this study, we focused on the effects of macrocyclic core size and the chemical properties of side chains attached to macrocyclic cores as well as solute concentrations on the hexagonal geometry of self-assembled monolayers. STM observations at the 1,2,4-trichrolobenzene/graphite interface revealed that PEM-C6 formed a honeycomb structure by van der Waals interactions between the interdigitated alkyl chains. However, upon increasing solute concentration, it changed to more dense hexagonal structure (tentatively called loose hexagonal structure I). In contrast, PBM-C8 formed loose hexagonal structure II of a slightly different packing mode at low concentration, while at high concentration it formed a high-density hexagonal structure in which alkyl chains are not adsorbed on the surface (dense hexagonal structure). In the dense hexagonal structure, macrocyclic cores are linked by hydrogen bonds between the ester carbonyl oxygen and the aromatic hydrogen atoms of the neighboring macrocycles. The packing geometries of loose hexagonal structures of PEM-C6 and PBM-C8 are different due to the different distance between the attachment of the alkyl ester groups which are located in confined space. On the other hand, PEM-TEG and PBM-TEG formed dense hexagonal structures, similar to PBM-C8 at high concentration, with their TEG units not adsorbed on the surface.
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