| Abstract
| - Three double-decker complexes of cerium(IV) were synthesized, which commonly have a 5,10,15,20-tetrakis(4-docosyloxyphenyl)porphyrin (C22OPP) moiety as one of the two tetrapyrrole rings. The three complexesCe(Pc)(C22OPP), Ce(C22OPP)2, and Ce(BPEPP)(C22OPP)are distinguished by the other rings, which are Pc (=phthalocyanine),C22OPP, and BPEPP (=5,15-bis[4-(phenylethynyl)phenyl]porphyrin), respectively. The rate of inter-ring rotation ofCe(BPEPP)(C22OPP) was estimated to be ∼3 s-1 in solution at room temperature. These complexes assemble intoordered arrays at the interface of 1-phenyloctane and the highly oriented pyrolytic graphite surface, owing to theaffinity of the long alkyl chains toward the surface, as revealed by means of scanning tunneling microscopy (STM)with molecular resolution. The shape of the upper ring is reflected in the STM image. Thus, Ce(Pc)(C22OPP), Ce(C22OPP)2, and Ce(BPEPP)(C22OPP) were observed as circular, square, and elliptic features, respectively. Possiblemolecular arrangements in the array of Ce(BPEPP)(C22OPP) are proposed by comparing STM images and molecularmodels. In the mixed arrays of Ce(BPEPP)(C22OPP) and H2(C22OPP), the double-decker complexes were distinguishedby brighter features. Competitive adsorption experiments showed that the adsorption of Ce(BPEPP)(C22OPP) is lessfavorable than that of H2(C22OPP) by ΔGapp = 2.7 kJ mol-1. Ce(BPEPP)(C22OPP) molecules appeared elliptic whenplaced within their own row, while they appeared isotropic when flanked by H2(C22OPP) molecules. Implications ofthe differences in the observed shapes to the inter-ring rotation are discussed.
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