Controlled Self-Assembly of Hexa-peri-hexabenzocoronenes in Solution

• Published in: Journal of the American Chemical Society Vol. 126; no. 36; pp. 11311 - 11321
• Main Authors: WU, Jishan, FECHTENKöTTER, Andreas, GAUSS, Jürgen, WATSON, Mark D., KASTLER, Marcel, FECHTENKöTTER, Chrys, WAGNER, Manfred, MüLLEN, Klaus
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 15.09.2004; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Experimental determinations of smectic, nematic, cholesteric, and other structures; Liquid crystals; Physical Sciences; Physics; Science & Technology; Structure of solids and liquids; crystallography; AROMATIC-AROMATIC INTERACTIONS; PHENYLENE ETHYNYLENE OLIGOMERS; PI-PI STACKING; X-RAY; MONOMER-DIMER EQUILIBRIUM; BASIS-SETS; PHOTOPHYSICAL PROPERTIES; DISCOTIC LIQUID-CRYSTALS; DINUCLEAR RUTHENIUM COMPLEX; SOLID-STATE; Electron interaction; Molecular association; Molecular interaction; Molecular aggregation; Polycyclic aromatic compound; Experimental study; NMR spectroscopy; Condensed benzenic compound; Discotic liquid crystals; Dendritic structure; Organic compounds
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja047577r

Disc-shaped hexa-peri-hexabenzocoronenes (HBCs) peripherally substituted by flexible dodecyl chains (molecule 1) or rigid polyphenylene dendrons (molecules 2a, b and 3) were efficiently synthesized. Steric hindrance arising from the substituents, from less hindered dodecyl to bulky dendrons, was utilized to program the self-assembly of the HBC cores in solution. The high tendency of the hexadodecyl-substituted HBC 1 to aggregate was determined by concentration and temperature-dependent H-1 NMR spectroscopic measurements and nonlinear least-squares analysis of the experimental data. The rigid dendrons in molecule 2a suppress the pi-pi interactions of the HBC cores to a certain extent, and a slow (with respect to the NMR time scale) monomer-dimer equilibrium is observed. This unique equilibrium was further controlled by temperature, concentration, and solvent to afford discrete monomeric or dimeric species. Further structural modifications such as the replacement of dodecyl groups in 2a with hydrogen atoms resulted in a stable dimer structure in 2b due to diminished steric hindrance, as supported by quantum chemical calculations. "Moving" the dendron arms closer to the HBC core gives molecule 3, which exists only as a nonaggregated monomer. UV-vis absorption and fluorescence spectra of these discrete species revealed obvious differences in their electronic and optoelectronic properties which can be explained by the existence or absence of pi-pi interactions.