Synthesis, Structure, and Optical Properties of Terminally Sulfur-Functionalized Core-Substituted Naphthalene-Bisimide Dyes

Abstract

The synthesis, characterization, and optical properties of a series of new 2,6-disubstituted naphtha- lene-bisimide dyes as molecular rods comprising terminal AcS groups is reported. The first series of dyes (1 - 3), comprising phenylhetero (Ph-X) core substituents, cover a broad range of the VIS spectrum, rang- ing from yellow (2) over red (3) to blue (1). The second series of dyes contains benzylhetero (Bn-X) core substituents (4 - 7). For the same heteroatom connecting the substituent to the naphthalene core, both series were found to display comparable colors. For the second series, the colors were blue (4), red (5), and violet (6, 7). The Ph-X-substituted dyes 1 - 3 are nonfluorescent, in contrast to the Bn-X-substi- tuted compounds 4 - 7. This rich variety of optical features that can be adjusted by rather small alterations of the core substituents makes these structurally very comparable molecular rods ideal candidates for optically triggered molecular-transport investigations. Also, thanks to the terminal AcS groups, these compounds can be placed between nobel-metal electrodes for optically triggered transport experiments. Introduction. - In the last few years, several terminally sulfur (S)-functionalized molecules have been successfully immobilized on a single-molecule level between two electrodes, and correlations between their molecular structures and electronic- transport properties have been revealed to some extent (1) (2). A current challenge is to extend such molecular-electronic-transport arrangements with an additional signal capable of triggering the current through the molecular structure. First examples of a single-molecule device responding to an electrochemical trigger have already been reported (3 - 5). Alternatively, light may also serve as an external trigger of the elec- tronic current. While molecular switches (6) and shuttles (7) between different electro- des have already been reported, our current focus is to combine electronic excitation of the immobilized molecule with electronic transport. In particular, we strive towards the investigation of optically triggered currents through single molecules, and of single- molecule electroluminescence. Against this background, our interest in rod-like and terminally S-functionalized dye molecules becomes reasonable. Herein, we report the synthesis, structural analysis, and optical properties of a series of core-substituted naphthalene-bisimide dyes, i.e., the rod-like compounds 1 - 7, com- prising terminal acetyl (Ac)-protected S-atoms.