Coincidence of the Molecular Organization ofβ-Substituted Oligothiophenes in Two-Dimensional Layers and Three-Dimensional Crystals

Abstract

The molecular arrangements of three different alkyl-substituted oligothiophenes both in two-dimensional adsorbed layers at a substrate interface and in bulk three-dimensional crystals were studied. Scanning tunneling microscopy (STM) was used to investigate the ordering of the conjugated oligomers in two-dimensional layers adsorbed on graphite. These data were compared with the X-ray structure determinations of single crystals revealing the arrangement in the three-dimensional bulk material. Quaterthiophenes 1 and 2, bearing dodecyl and hexyl side chains, respectively, exhibit a lamella-type stacking of the conjugated backbone concomitant with an interlocking of the alkyl side chains both on the surface and in the crystal. In contrast, the arrangement of propyl-substituted quaterthiophene 3 is rather "herringbone-like" due to the reduced interactions of the shorter alkyl side chains. In all three cases, evidently, the two-dimensional ordering at the graphite surface is coincident with the molecular packing in one cross-section of the three-dimensional crystal.

Direct Observation of Alkyl Chain Interdigitation in Conjugated Polyquarterthiophene Self‐Organized on Graphite Surfaces

“…This suggests the possibility of the dodecyl chains of PQT-12 guiding the alignment of polymer on the surface, which is the typical case for alkane or alkyl-substituted molecules. [29][30][31][32][33] On higher resolution imaging, the apparent chain packing of the polymers can be observed, as shown in Figure 2. These lamellae features appeared to have a zigzag formation, with obvious dodecyl chain interdigitation between adjacent neighboring chains, separated by a distance of 2.2 nm.…”

“…[35] Azumi et al had reported the close relation of single-crystal XRD studies and STM investigations on b-substituted oligothiophenes. [33] These molecules were observed to possess the same molecular order on a two-dimensionally organized monolayer on the HOPG surface as one layer of its threedimensional crystal. Single-crystal XRD studies carried out on monomer PQT-12 units also appeared to adopt similar structural packing order as that in our STM imaging results.…”

“…Single-crystal XRD studies carried out on monomer PQT-12 units also appeared to adopt similar structural packing order as that in our STM imaging results. [30,33] On comparing the STM imaging results of the selfassembly of PQT-12 on HOPG surface with our previous AFM studies as reported in Beng et al, it can be observed that although the PQT-12 chains assemble in a flat-lying orientation in STM imaging and edge-on orientation as proposed from AFM investigations, both arrangements appear to adopt similar alkyl chain interdigitated structures. [13,21] Both the monolayer observed in STM imaging and the vertical layer of the lamellar p-p stacking proposed from AFM imaging seemed comparable.…”

Charge Delocalization in Oligomers of Poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT)

“…This feature has been reported in the case of crystals of thiophene-based oligomers, for example, didodecylquaterthiophenes (DDQT). [43][44][45] In the case of available single-crystal structures of BTTT1 and BTTT2, only trans configurations have been observed to date. 46 As a result, we have chosen to focus here on the trans isomers.…”

Self-Assembly of Alkyl-Substituted Oligothiophenes on MoS2: A Joint Experimental/Theoretical Study

“…DOTT also forms stable and ordered monolayers. According to the electronic nature of the aromatic and aliphatic moieties, it can again be concluded that the brighter parts correspond to the oligothiophene π-system 24,45 and the alkyl chains are supposed to lie down between the brighter parts.…”