Solvent dependent supramolecular self-assembly and surface reversal of a modified porphyrin

In this paper, a novel core-modified porphyrin with meso-aryl substituents and phenanthrene-fused pyrrole rings (N2S2-OR) is synthesized. Scanning tunneling microscopy (STM) has been used to probe its self-assembly behavior on a highly-oriented pyrolytic graphite (HOPG) surface. Our STM results have shown that there is an obvious solvent-dependent self-assembly for the surface-confined target molecules. In n-tetradecane, N2S2-OR assembles into a perfect alternating structure. At the 1-phenyloctane-graphite interface, disordered structures are formed and nonperiodic alternation is observed, whereas the target molecule in 1-heptanoic acid is assumed to form homogeneous close-packed monolayers with no alternating. Interestingly, such solvent-dependent supramolecular assembled behavior also involves the structural transformation of the backbone of the core-modified porphyrin derivative from saddle to reversed-saddle in these three solvents with different polarities.