Self-assembled islands of 5,10,15,20-tetrakis(pentafluoro-phenyl)porphyrin (2HTFPP) on Au(111) contain two bistable molecular species that differ by shifted electronic energy levels.

A microcontroller was used to operate a pulsed-solenoid valve connected directly to a vacuum chamber (10−8mbar) to deposit microliters of solution resulting in monolayer and submonolayer coverage of the substrate. This technique is particularly suited for preparing samples to be characterized by scanning tunneling microscopy or atomic force microscopy. The microcontroller can be programed to open the valve at the millisecond timescale. The valve is particularly suited to deliver air and temperature sensitive molecules to the substrate without the need to remove the substrate from vacuum for deposition.

Porphyrins and tetrapyrroles play crucial roles in biological processes such as photosynthesis and molecular transport. These nature-based molecules have found application in artificial systems, such as sensing, catalysis, and 2D/3D networks. They are ideal building blocks due to their chemical diversity, stability, and ability to self-assemble on surfaces. Derivatization of the peripheral positions allows for the rational design of magnetic, catalytic, and photochemical properties. Due to this, porphyrins have been used in a variety of natural and artificial systems such as photodynamic therapies and dye-sensitized solar cells. Recently, much work and attention have focused on using specific porphyrin and molecular relatives for molecular electronics due to their robust nature, functionality, and synthesis. The focus of this review is to summarize the mechanisms that affect the internal structure and properties of the molecules and how changes in the local chemical environment alter the electronic properties of the porphyrin. We review the current state of the literature concerning the intermolecular and surface-adsorbate interactions that dictate self-assembly. We will assess the effects that molecule-molecule and molecule-substrate interactions play on the molecule’s properties and the effects that external forces have on the molecular properties. The goal of this review is to dissect the mechanisms responsible for the unique properties that arise from porphyrinic systems adsorbed on surfaces.

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Solution deposition of a 5,10,15,20-Tetrakis-(4-bromophenyl)-porphyrin (TBrPP) and dichloromethane (DCM) on Au(111) produces self-assembled islands with non-random orientation that is directed by the gold herringbone reconstruction of Au(111). Annealing to 230°C...