All-trans-retinoic acid (ReA), a closed-shell organic molecule comprising only C, H, and O atoms, is investigated on a Au(111) substrate using scanning tunneling microscopy and spectroscopy. In dense arrays single ReA molecules are switched to a number of states, three of which carry a localized spin as evidenced by conductance spectroscopy in high magnetic fields. The spin of a single molecule may be reversibly switched on and off without affecting its neighbors. We suggest that ReA on Au is readily converted to a radical by the abstraction of an electron.

The self-assembly of 3,10-dibromo-perylo­[1,12-b,c,d]­thiophene on Ag(111) leads to three types of ordered porous networks: honeycomb PN1, Kagome PN2, and hybrid PN3. Detailed experimental and theoretical analyses confirm the thermal stability order of the three constructed porous networks. High-resolution scanning tunneling microscopy images indicate the importance of two σ-hole interactions of Br···S and Br···Br in steering two-dimensional molecular assembly on metal surfaces.

The adsorption and assembly of individual and submonolayered TiOPc on Ag(111), Cu(111), and Au(111) have been investigated by scanning tunneling microscopy (STM) and spectroscopy. High resolution STM imaging as well as dI/dV and I−z measurements reveal that TiOPc adsorbed on Ag(111) adopts either O-up or O-down configuration. An intermolecular dipole−dipole interaction leads to the fact that neighboring TiOPc molecules in alternating O-up and O-down configurations form a highly ordered checkerboard assembly structure on Ag(111). However, no large size TiOPc assemblies are observed on Cu(111) and Au(111) due to low surface mobility and diffusivity caused by strong TiOPc−Cu(111) interaction and the templating effect by the reconstructed herringbone structure of Au(111), respectively. Instead, molecular dimers on both Au(111) and Cu(111) as well as molecular aggregates on Au(111) are routinely observed in experiments, indicating that the intermolecular dipole−dipole attraction and weak hydrogen bonding coplay an important role in steering the adsorption and assembly of the TiOPc molecules on the coinage metal surfaces.