Abstract
The coverage-dependent adsorption of a racemic mixture of [7]thiaheterohelicene-2,13-carboxaldehyde on Au(111), Cu(001), and NiAl(110) surfaces was investigated using a scanning tunneling microscope (STM). At a low coverage, the adsorption process for helicene molecules on Au(111) was strongly affected by surface reconstruction. At monolayer saturation coverage, the dominant molecular structure observed on Au(111) characteristically had separated self-assembled twin rows aligned in ⟨112̅⟩ directions. The helicene molecules within these separated twin rows are preferentialy arranged in a zigzag pattern with alternating (M)- and (P)-enantiomers. With increasing molecular coverage, the molecular structural transition from self-assembled twin rows to self-assembled single rows was observed. STM-induced light emission (STM-LE) investigation of helicene molecules on Au(111) showed the suppression of plasmon light emission over the molecules. The adsorption of helicene molecules on Cu(001) and NiAl(110) was quite different from that observed on Au(111). Neither the formation of self-assembled twin rows nor the molecular arrangement into different domains was observed. The formation of molecular clusters on Cu(001) and NiAl(110) was observed. STM-LE investigation of helicene molecules adsorbed on Cu(001) showed the suppression of plasmon light emission over these molecules. In contrast to metallic Au(111) and Cu(001) substrates, STM-LE investigations revealed the enhancement of light emission above the molecular clusters formed on metallic NiAl(110), suggesting plasmon-enhanced molecular light emission.
Highlights
Crystallization of chiral molecules on solid substrates imaged using a scanning tunneling microscope (STM) is a promising approach to improve our understanding of the basic principles underlying the processes of spontaneous resolution and chiral recognition.1−16 Heptahelicene, a model chiral molecule used in STM observations to clarify the above processes,16,17 belongs to a class of nonplanar screw-shaped molecules exhibiting left- and right-handed helicities formed from ortho-fused aromatic rings.18−22 Note that the progress in the field of helicene functionalization made it possible to design and fine-tune helicene derivatives of desired application properties
Pasteur’s famous experiment was repeated on the single-molecule scale on racemic heptahelicene adsorbed on Cu(111) by STM-tip-induced manipulation, revealing a strong preference for the formation of heterochiral pairs at a low coverage
We report investigation of the adsorption of a racemic mixture of [7]thiaheterohelicene-2,13-carboxaldehyde on Au(111), Cu(001), and NiAl(110) surfaces, as well as the detection of light emission from molecules induced by the STM tip
Summary
Crystallization of chiral molecules on solid substrates imaged using a scanning tunneling microscope (STM) is a promising approach to improve our understanding of the basic principles underlying the processes of spontaneous resolution and chiral recognition.− Heptahelicene, a model chiral molecule used in STM observations to clarify the above processes, belongs to a class of nonplanar screw-shaped molecules exhibiting left- and right-handed helicities formed from ortho-fused aromatic rings.− Note that the progress in the field of helicene functionalization made it possible to design and fine-tune helicene derivatives of desired application properties. In particular, investigations of racemic heptahelicene adsorption on Cu(111), Au(111), and Ag(111) showed no separation of molecular structures into homochiral domains; they showed the formation of selfassembled twin rows consisting of alternating enantiomers. In contrast, the adsorption of racemic heptahelicene onCu(001) resulted in the formation of homochiral domains. Enantiomorphism was discovered for enantiomeric pure heptahelicene on Cu(111). Pasteur’s famous experiment was repeated on the single-molecule scale on racemic heptahelicene adsorbed on Cu(111) by STM-tip-induced manipulation, revealing a strong preference for the formation of heterochiral pairs at a low coverage. Investigations of racemic heptahelicene adsorption on Cu(111), Au(111), and Ag(111) showed no separation of molecular structures into homochiral domains; they showed the formation of selfassembled twin rows consisting of alternating enantiomers.. Cu(001) resulted in the formation of homochiral domains.. Pasteur’s famous experiment was repeated on the single-molecule scale on racemic heptahelicene adsorbed on Cu(111) by STM-tip-induced manipulation, revealing a strong preference for the formation of heterochiral pairs at a low coverage. One very important problem that arises during STM investigations of chiral molecules is the determination of the spatial arrangement of chemical moieties around a given protrusion to identify molecular chirality.. One very important problem that arises during STM investigations of chiral molecules is the determination of the spatial arrangement of chemical moieties around a given protrusion to identify molecular chirality. Only high-resolution STM imaging with submolecular
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