The synthesis of perylene 3,4:9,10-tetracarboxylic acid bisimides (PBIs) dendronized with first generation dendrons containing 0 to 4 methylenic units (m) between the imide group and the dendron, (3,4,5)12G1-m-PBI, is reported. Structural analysis of their self-organized arrays by DSC, Xray diffraction, molecular modeling and solid state 1H-NMR was carried out on oriented samples with heating and cooling rates of 20 to 0.2 °C/min. At high temperature (3,4,5)12G1-m-PBI self-assemble into 2D- hexagonal columnar phases with intracolumnar order. At low temperature they form orthorhombic (m = 0, 2, 3, 4) and monoclinic (m = 1) columnar arrays with 3D periodicity. The orthorhombic phase has symmetry close to hexagonal. For m = 0, 2, 3, 4 they consist of tetramers as basic units. The tetramers contain a pair of two molecules arranged side by side and another pair in the next stratum of the column, turned upside-down and rotated around the column axis at different angles for different m. In contrast, for m = 1 there is only one molecule in each stratum, with a four-strata 21 helical repeat. All molecules face up in one column, and down in the second column of the monoclinic cell. This allows close and extended π-stacking, unlike in the disruptive up-down alteration from the case of m = 0, 2, 3, 4. Most of the 3D structures were observed only by cooling at rates of 1 °C/min or less. This complex helical self-assembly is representative for other classes of dendronized PBIs investigated for organic electronics and solar cells.
Citation: Journal of the American Chemical Society
Pub Type: Journals
organic electronics, self assembly, photovoltaics