Self-Assembly of Electron Donor−Acceptor Dyads into Ordered Architectures in Two and Three Dimensions:  Surface Patterning and Columnar “Double Cables”

Abstract

We report the synthesis and characterization of covalent dyads and multiads of electron acceptors (A) and donors (D), with the purpose of exploiting their nanophase separation behavior toward (a) two-dimensional (2D) surface patterning with well-defined integrated arrays of dissimilar molecular electronic features and (b) bulk self-assembly to noncovalent columnar versions of the so-called "double cable" systems, the likes of which could eventually provide side-by-side percolation pathways for electrons and holes in solar cells. Soluble, alkylated hexa-peri-hexabenzocoronenes (HBCs) bearing tethered anthraquinones (AQs) are shown by scanning tunneling microscopy (STM) to self-assemble at the solution-graphite interface into either defect-rich polycrystalline monolayers or extended 2D crystalline domains, depending on the number of tethered AQs. In the bulk, the thermal stability of the room-temperature HBC columnar phase is increased, which is attributed to the desired nanotriphase separation of HBC columns, insulating alkyl sheaths, and AQ units. Homeotropic alignment (columns normal to surfaces), predicted to be ideal for potential exploitation of such "double cables" in photovoltaic devices, is demonstrated.

Self-Assembly of Small Polycyclic Aromatic Hydrocarbons on Graphite: A Combined Scanning Tunneling Microscopy and Theoretical Approach

“…12 The versatility of STM is limited only by its inability to distinguish different chemical groups or atoms; however related techniques such as scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy can in principle provide unique electronic or vibrational signatures for surface atoms and adsorbate functional groups. 12,[22][23][24][25][26][27][28][29][30] Numerous STM studies have focused on understanding the spontaneous self-assembly of molecules on surfaces, including the physisorbed monolayers formed at the liquid-graphite interface 1,[3][4][5][8][9][10]18,21,28,[31][32][33][34][35][36][37][38][39][40][41] and the vacuum-graphite interface. [23][24][25][42][43][44][45][46][47][48][49][50][51][52] Information about the factors that promote twodimensional self-assembly, such as van der Waals forces, electrostatic forces, and hydrogen-bonded...…”

“…2,6,[22][23][24]26,28,29,[34][35][36][37][38]42,43,[53][54][55][56] These molecules have attracted attention in the context of charge transport as materials for molecular electronic device applications. Aromatic molecules, whose conductivity occurs via the π-system, can behave as either electron donors or acceptors, depending on their functionalization.…”

Nanoscale assembly into extended and continuous structures and hybrid materials

“…52 Assembly of HBC bearing five alkyl substituents and one anthraquinone moiety on graphite led to void defects in long range order, as revealed by scanning tunneling microscopy. This sharply contrasts the well-organized, defect-free hexagonal arrangement observed for HBC-dimethoxyanthracene dyads or HBC molecules bearing six anthraquinones.…”

Effects of side-chain length on the magnetic response of discotic metallomesogens

“…Therefore, DLCs have been investigated for opto-electronic applications such as photovoltaic cells (SchmidtMende et al, 2001;Samori et al, 2004), field-effect transistors Jä ckel et al, 2004;Pisula et al, 2005) and organic light-emitting diodes (Seguy et al, 2000;O'Neill & Kelly, 2003). However, for practical applications, long-range unidirectional alignment of the columnar DLC structure is crucial.…”