Generating Long Supramolecular Pathways with a Continuous Density of States by Physically Linking Conjugated Molecules via Their End Groups

Abstract

Self-assembly of conjugated 2,5-dialkoxy-phenylene-thienylene-based oligomers on epitaxial monolayer graphene was studied in ultrahigh vacuum by low-temperature scanning tunneling microscopy (STM). The formation of long one-dimensional (1D) supramolecular chain-like structures has been observed, associated to a physical linking of their ends which involved the rotation of the end thiophene rings in order to allow π-π stacking of these end-groups. dI/dV maps taken at an energy corresponding to the excited states showed a continuous electronic density of states, which tentatively suggests that within such molecular chains conjugation of electrons is preserved even across physically linked molecules. Thus, in a self-organization process conjugation may be extended by appropriately adapting conformations of neighboring molecules. Our STM results on such self-organized end-linked molecules potentially represent a direct visualization of J-aggregates.

A new growth process for crystalline ultra-thin layers of conjugated oligomers used in field-effect transistor applications

“…For example, due to the weaker interactions between side-chains crystal growth along the direction of the side-chains is expected to be much slower. 5TBT molecules are terminated by thiophenes at the ends, allowing for strong interactions with neighbouring molecules, as has been shown by Shokri et al [14]. In full agreement with these expectations, thin needle-like crystals of 3TBT (consisting of three TBT monomers) have been grown in solution [15].…”

When 2D Materials Meet Molecules: Opportunities and Challenges of Hybrid Organic/Inorganic van der Waals Heterostructures

“…Several groups have studied the process of molecular self‐assembly on graphene in the real space by scanning tunneling microscopy . These studies often focused epitaxial graphene grown onto metallic or semiconducting SiC surfaces, and recently also on graphene transferred onto insulating SiO 2 or BN …”

“…While in several cases the molecular assembly and its properties represent the main focus of STM studies, only a few reports address the effects of a given molecular assembly on the electronic properties of 2DMs . In these cases, an STM study of the molecular assembly on a 2DM (typically graphene) is combined to the investigation of the electrical properties of the same system, addressed at the macroscopic level (for instance, in devices).…”

“…The interactions of molecular layers with the inert surface of 2DM are mediated by vdW forces analogous to those between different inorganic sheets, so that similar interface effects can be envisaged in both cases, making organic/inorganic architectures the hybrid equivalent of fully inorganic vdWHs. The analogy is even more profound if one considers that crystalline molecular monolayers can be obtained on 2DMs that can be integrated in complex multilayered heterostructures composed of alternating organic/inorganic single layers.…”

Oligothiophene/graphene supramolecular ensembles managing light induced processes: preparation, characterization, and femtosecond transient absorption studies leading to charge-separation

“…A great advantage of such organics is the versatility of their chemistry and their low cost as starting materials. 29 Additionally, the molecular assembly of tetrathiophenes and the impact of the morphology of CVD graphene was also reported. Since the early 90's, the scientific interest for these materials increased the attentiveness for new synthetic routes, molecular designing and a stepwise transition from bulk materials to well-defined structures.…”