Visualization of Various Supramolecular Assemblies of Oligo(para-phenylenevinylene)-Melamine and Perylene Bisimide

• Published in: Chemistry : a European journal Vol. 14; no. 28; pp. 8579 - 8589
• Main Authors: Hoeben, Freek J. M., Zhang, Jian, Lee, Cameron C., Pouderoijen, Maarten J., Wolffs, Martin, Würthner, Frank, Schenning, Albertus P. H. J., Meijer, E. W., De Feyter, Steven
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26-09-2008; WILEY‐VCH Verlag
• Subjects: chirality; donor-acceptor systems; hydrogen bonds; scanning probe microscopy; self-assembly
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200800760

A melamine derivative has been covalently equipped with two oligo(para‐phenylenevinylene) (OPV) chromophores. This procedure yields a bifunctional molecule with two hydrogen‐bonding arrays available for complementary binding to perylene bisimide derivatives. Depending on the solvent, hydrogen‐bonded trimers, tetramers, and dimers on a graphite surface are observed for pure OPV–melamine by using scanning tunneling microscopy (STM). Upon the addition of perylene bisimide, linear tapes of perylene bisimide, 12‐membered rosettes that consist of alternating hydrogen‐bonded OPV–melamine and perylene bisimide moieties are visualized. These results provide direct evidence for the possible modes of hydrogen bonding within a supramolecular co‐assembly in solution. Subsequently, the optical properties of pure OPV–melamine and co‐assemblies with a perylene bisimide derivative were characterized in solution. In an apolar solvent, OPV–melamine self‐assembles into chiral superstructures. Disassembly into molecularly dissolved species is reversibly controlled by concentration and temperature. Complementary hydrogen bonding to a perylene bisimide derivative in an apolar solvent yields multicomponent, π‐stacked dye assemblies of enhanced stability that are characterized by fluorescence quenching of the constituent chromophores. Titration experiments reveal that a mixture of hydrogen‐bonded oligomers is present in solution, rather than a single discrete assembly. The solution experiments are consistent with the STM results, which revealed various supramolecular assemblies. Our system is likely not to be optimally programmed to obtain a discrete co‐assembled structure in quantitative yield.
Super rosettes: Complementary hydrogen bonding occurs between an oligo(para‐phenylenevinylene)‐functionalized melamine species and a perylene bisimide derivative. Besides other structures, the formation of 12‐membered supramolecular donor–acceptor rosettes is observed with scanning tunneling microscopy (see picture). The hydrogen‐bonded structures π stack into chiral co‐assemblies in solution. It is difficult, however, to “complete the circle” in both situations.