The controlled attachment of chromophores to metal or semiconducting surfaces is a prerequisite for the construction of photonic devices and artificial surface-based light-harvesting systems. We present an approach to mount porphyrins in ordered monolayers on Au(111) by self-assembly and verify it, employing STM, absorption spectroscopy, and quantum chemical calculations. The usual adsorption geometry of planar chromophores, flat on the surface or densely packed edge-on, is prevented by mounting the porphyrins upright on a molecular platform. An ethynyl unit as spacer and pivot joint provides almost free azimuthal rotation of the unsubstituted porphin. However, rotation of the larger triphenylporphyrin unit is sterically restricted: because the diameter of the substituted porphyrin is larger than the distance to its next neighbors, the phenyl substituents of neigboring molecules interact by dispersion force, which leads to an alignment of the azimuthal rotators.

Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA.

The conductances of molecular model junctions comprising a triazatriangulenium platform with or without an ethynyl spacer and an upright Zn-porphyrin are probed with a low-temperature scanning probe microscope. The platform alone is found to be highly conductive. The ethynyl-linked Zn-porphyrin moiety reduces the conductance by three orders of magnitude and leads to an unexpected, non-monotonous variation of the force that was measured simultaneously at the tip of the microscope. Density functional theory calculations show that this variation results from an induced tilting of the porphyrin. ExperimentExperiments were performed in a combined STM/AFM in UHV at 5 K with a base pressure of × − 5 10 mbar 11 . The AFM was operated in a non-contact frequency-modulation mode with a tuning fork probe [11]. The free OPEN ACCESS RECEIVED