Rotational Libration of a Double-Decker Porphyrin Visualized

Abstract

Scanning tunneling microscopy has revealed the reorientation of one of the macrocyclic rings of the double-decker porphyrin complex [Ce(TPP-Fc)(C(22)OPP)] [TPP-Fc = 5-(4-(4-ferrocenylphenylethynyl)phenyl)-10,15,20-triphenylporphyrin; C(22)OPP = 5,10,15,20-tetrakis(4-docosyloxyphenyl)porphyrin] by 90 degrees between scans when the other ring is fixed on a surface. This libration was evidenced by monitoring the location of the appended ferrocene unit, which functioned as a molecular beacon signaling its position.

Monolayer Assemblies of a Sandwich-Type Double-Decker Porphyrin Complex of Cerium with an Additional Pendant Porphyrin Unit

“…Similar effects were also observed in the case of [Ce(C 22 OPP)(TPP-Fc)], for which the ferrocene unit appeared higher in the pure array of the molecules than in the matrix of H 2 (C 22 OPP). 25 We have rarely encountered the parallel orientation for the present double-decker complex, in which the free-base porphyrin units are directed along the molecular row (see Fig. 1(b)).…”

“…It was also hoped that the rotational behavior of the upper TPP-TPP fragment could be analyzed by making room around the double-decker complex, as was successfully done for [Ce(C 22 OPP)(TPPFc)], 25 which turned out to be difficult for the present molecule as described below. Figure 5 shows a couple of typical STM images prepared from a mixed solution of [Ce(C 22 OPP)(TPP-TPP)]…”

“…Desorption and adsorption were much slower for previously reported double-decker complex, [Ce(C 22 OPP)(TPP-Fc)], which has exactly the same structure, except for the pendant group. 25 Another doubledecker complex with the same porphyrin ligand for adsorption, [Ce(C 22 OPP)(BPEPP)] also afforded stable mixed monolayers with H 2 (C 22 OPP). 24 We may infer from the comparison of the behaviors of these molecules that apparently innocent groups not directly involved in adsorption may have profound effects on the adsorption and assembling properties of the molecule.…”

“…8 9 The four potential minima are of course equivalent if both tetrapyrrole ligands have four-fold symmetry, as is usually the case. What we used as components in double-decker complexes include 5,15-bis [4-(phenylethynyl)phenyl]porphyrin (BPEPP) 23 24 and 5-[4-(4-ferrocenylphenyl)ethynylphenyl]-10,15,20-triphenylporphyrin (TPP-Fc) 25 (Fig. 2).…”

Coordination Programming: A New Concept for the Creation of Multifunctional Molecular Systems

“…7 Otsuki et al directly observed rotation of double-decker complexes on a surface using STM and evaluated the rotation rate (Figure 3). 8 Makiura et al reported the layer-by-layer surface preparation of a two-dimensional metalorganic framework (MOF) comprising a LangmuirBlodgett film of a network of porphyrin and copper ions. 9 Nishihara, Sasaki, Nakazato, and co-workers recently synthesized π-conjugated metal complex nanosheets comprising nickel bis(dithiolene) units via an interfacial reaction system containing the ligand in an organic layer and the metal ion in an aqueous layer.…”