This paper is derived from our concluding remarks presentation and the ensuing conversations at the Faraday Discussions meeting on Complex Molecular Surfaces and Interfaces, Sheffield, UK, 24th–26th July 2017. This meeting was comprised of sessions on understanding the interaction of molecules with surfaces and their subsequent organisation, reactivity or properties from both experimental and theoretical perspectives. This paper attempts to put these presentations in the wider context and focuses on topics that were debated during the meeting and where we feel that opportunities lie for the future development of this interdisciplinary research area.

The effect of diffusion-controlled microfluidic conditions in the very initial stages of a far-from-equilibrium self-assembly process on the evolution of aggregate chirality in a multicomponent supramolecular system is shown.

A series of chiral synthetic compounds is reported that shows intricate but specific hierarchical assembly because of varying positions of coordination and hydrogen bonds. The evolution of the aggregates (followed by absorption spectroscopy and temperature-dependent circular dichroism studies in solution) reveal the influence of the proportion of stereogenic centers in the side groups connected to the chromophore ring in their optical activity and the important role of pyridyl groups in the self-assembly of these chiral macrocycles. The optical activity spans 2 orders of magnitude depending on composition and constitution. Two of the aggregates show very high optical activity even though the isolated chromophores barely give a circular dichroism signal. Molecular modeling of the aggregates, starting from the pyridine–zinc(II) porphyrin interaction and working up, and calculation of the circular dichroism signal confirm the origin of this optical activity as the chiral supramolecular organization of the molecules. The aggregates show a broad absorption range, between approximately 390 and 475 nm for the transitions associated with the Soret region alone, that spans wavelengths far more than the isolated chromophore. The supramolecular assemblies of the metalloporphyrins in solution were deposited onto highly oriented pyrolitic graphite in order to study their hierarchy in assembly by atomic force microscopy. Zero and one-dimensional aggregates were observed, and a clear dependence on deposition temperature was shown, indicating that the hierarchical assembly took place largely in solution. Moreover, scanning electron microscopy images of porphyrins and metalloporphyrins precipitated under out-of-equilibrium conditions showed the dependence of the number and position of chiral amide groups in the formation of a fibrillar nanomaterial. The combination of coordination and hydrogen bonding in the complicated assembly of these molecules—where there is a clear hierarchy for zinc(II)-pyridyl interaction followed by hydrogen-bonding between amide groups, and then van der Waals interactions—paves the way for the preparation of molecular materials with multiple chromophore environments.

Coordination-driven gelation of a benzothiadiazole-fused tetrathiafulvalene (TTF) is demonstrated. This is the first work reporting highly stable metallogels based on a donor–acceptor conjugate with such a simple structure for the construction of new low-bandgap materials with various functional properties and novel nanostructures.

Correction for ‘Coordination-directed self-assembly of a simple benzothiadiazole-fused tetrathiafulvalene to low-bandgap metallogels' by Anneliese M. Amacher et al., Chem. Commun., 2015, 51, 15063–15066.

Changing abruptly the potential between a scanning tunneling microscope tip and a graphite substrate induces “high-conductance” spots at the molecular level in a monolayer formed by a manganese chloride–porphyrin molecule. These events are attributed to the pulse-induced formation of μ-oxo-porphyrin dimers. The pulse voltage must pass a certain threshold for dimer formation, and pulse polarity determines the yield.

A combination of crystallographic and spectroscopic techniques has been used in order to address thorough purification protocols for a series of atropisomeric 1,1′-binaphthalene-2,2′-diol (BINOL) derivatives to be used as building blocks for chiral nanoscale constructs. The compounds were obtained following an initial electrophilic aromatic bromination reaction at the 6,6′ position of BINOL, which was used in either its racemic or its enantiopure form. The presence of regioisomeric compounds, in which bromine atoms are located at different positions of the naphthalene skeletons, could be hinted at by classical spectroscopy (1H NMR and IR) and fully confirmed by single-crystal X-ray analysis of the solids formed during crystal growth of the crude products, where solid solutions are identified in part due to the presence of bromine that is a relatively heavy atom. If purification by recrystallization in suitable solvents is not performed, further chemical elaboration by means of alkylation on the 2,2′-phenolic positions produces compounds in which the regioisomeric impurities are still present. The set of five X-ray structures highlights interesting packing features extremely useful for the crystal engineering of nanostructures integrating these axially chiral building blocks.

The heterocoupling of organic building blocks to give complex multicomponent macromolecules directly at a surface holds the key to creating advanced molecular devices. While “on-surface” synthesis with prefunctionalized molecules has recently led to specific one- and two- component products, a central challenge is to discover universal connection strategies that are applicable to a wide range of molecules. Here, we show that direct activation of C–H bonds intrinsic to π-functional molecules is a highly generic route for connecting different building blocks on a copper surface. Scanning tunneling microscopy (STM) reveals that covalent π-functional macromolecular heterostructures, displaying diverse compositions, structures and topologies, are created with ease from seven distinct building blocks (including porphyrins, pentacene and perylene). By exploiting differences in C–H bond reactivity in the deposition and heating protocols we also demonstrate controlled synthesis of specific products, such as block copolymers. Further, the symmetry and geometry of the molecules and the surface also play a critical role in determining the outcome of the covalent bond forming reactions. Our “pick-mix-and-link” strategy opens up the capability to generate libraries of multivariate macromolecules directly at a surface, which in conjunction with nanoscale probing techniques could accelerate the discovery of functional interfaces.Keywords: covalent assembly; C−H bond activation; on-surface synthesis; pentacene; perylene; porphyrins; surface chemistry;

Correction for ‘Coordination-directed self-assembly of a simple benzothiadiazole-fused tetrathiafulvalene to low-bandgap metallogels' by Anneliese M. Amacher et al., Chem. Commun., 2015, 51, 15063–15066.

Coordination-driven gelation of a benzothiadiazole-fused tetrathiafulvalene (TTF) is demonstrated. This is the first work reporting highly stable metallogels based on a donor–acceptor conjugate with such a simple structure for the construction of new low-bandgap materials with various functional properties and novel nanostructures.