Commensurate surface structures and concertedcis-trans-isomerization within ordered monolayers ofα-sexithiophene on Ag(001)

Abstract

The monolayer of ␣-sexithiophene on Ag͑001͒ has been studied by scanning tunneling microscopy and low-energy electron diffraction. Upon deposition at room temperature four well-ordered and commensurate molecular structures have been identified where the molecules adsorb flat lying with their long axis parallel to the ͓110͔ and ͓110͔ high-symmetry directions. Whereas three structures consist of straight molecules in alltrans configuration, one long-range ordered structure is observed where all molecules have undergone a trans-cis isomerization process between the second and third thiophene ring.

Gold diggers: Altered reconstruction of the gold surface by physisorbed aromatic oligomers

“…In both structures, α-6T molecules are packed in molecular rows, but in areas 1 and 3 the long molecular axis of the molecules is oriented almost perpendicular to the direction of 011601-4 the molecular rows, whereas in areas 2 and 4 it is at a 30 • angle [14]. This rotated structure strongly resembles the adsorption pattern of α-6T on Ag(100) [47], a surface that does not have any reconstruction.…”

From flat to tilted: gradual interfaces in organic thin film growth

“…[10][11][12][13] Morphology and electronic properties of α-6T on metal surfaces have been investigated from single molecule adsorption 14 to structural assembly and domain formation of monolayers. [15][16][17][18][19][20][21] The formation of flat monolayers has been found on all metal surfaces. Due to the prochirality of α-6T in its all-trans conformation, such a flat adsorption leads to the formation of two enantiomeric forms, the S and the R enantiomer (see Figure 1 (b)).…”

“…In the 1S domain the pattern can be assigned to an adsorbed α-6T molecule in the S-enantiomeric and in the 1R domain in the R-enatiomeric form. 20 Each domain accommodates exclusively one of the enantiomeric forms.…”

“…Note that the enantiomeric structure comprises the entire molecule-surface system, and not only the molecule. For monolayer coverage, formation of extended chiral domains that consist exclusively either of the S enantiomer or the R enantiomer has been reported for α-6T on Ag(100), 20 Ag(110), 22 Au(100), 21 and Au(111). 19 A commonly discussed driving force for the formation of homochiral domains is the minimization of steric repulsion and the subsequent increase in packing density; for a detailed discussion see Ref.…”

“…However, heterochiral monolayers consisting of R and S enantiomers have also been observed after thermally induced cis-trans-isomerization of α-6T molecules on Ag(100). 20 α-6T crystallizes in its low-temperature structure 23,24 depicted in Figure 1 (a) upon sublimation at low pressure.…”