Large All-Hydrocarbon Spoked Wheels of High Symmetry: Modular Synthesis, Photophysical Properties, and Surface Assembly

Abstract

In a convergent modular synthesis, a very efficient pathway to shape-persistent molecular spoked wheels has been developed and applied according to the covalent-template concept. The structurally defined two-dimensional (2D) oligo(phenylene-ethynylene-butadiynylene)s (OPEBs) presented here are about 8 nm sized hydrocarbons of high symmetry. 48 alkyl chains attached to the molecular plane (hexyl and hexadecyl, respectively) guarantee a high solubility of the compounds. The structure and uniformity of these defined, stable, D(6h) symmetrical compounds is verified by MALDI-MS, GPC analysis, and high-temperature (HT) (1)H and (13)C NMR. Detailed photophysical measurements of nonaggregated molecules in solution (as confirmed by dynamic light scattering (DLS)) focus on the identification of chromophores by comparison with suitable model compounds. Moreover, time-resolved measurements including fluorescence lifetime and depolarization support the chromophore assignment and reveal the occurrence of intramolecular energy transfer. Scanning tunneling microscope (STM) characterization at the solid/liquid interface demonstrates the efficient self-assembly of the OPEBs into hexagonal 2D crystalline layers with a periodicity determined by both the size of the OPEB backbone and the length of peripheral side chains. Atomic force microscope (AFM) studies show a very different assembly behavior of the two spoked wheel molecules, on both graphite and mica. While the hexyl-substituted wheel can form stacked superstructures, hexadecyl groups prevent any ordering in the film aside from the monolayer directly in contact with the surface.

Fluctuating exciton localization in giant π-conjugated spoked-wheel macrocycles

“…Identical results are found in wide-field microscopy, implying that the confocal laser excitation is free of polarisation distortion artefacts despite the high numerical aperture objective used 41 (see Supplementary Information for discussion).Comparison of the rings to LHII is also interesting: despite similar dimensions and symmetry, isotropic absorption is not seen in experiments involving single complexes36- 38 . Other synthetic ring structures have only been studied by ensemble fluorescence depolarisation15,21 , revealing ultrafast loss in polarisation memory, compatible with our single-molecule results.…”

Multiple‐Porphyrin Functionalized Hexabenzocoronenes

“…Given that transformations of hexa‐porphyrin‐HPB 10 to the corresponding HBC could not be achieved, a new strategy was developed in which the HBC was preformed before the attachment of the porphyrins (Scheme ). Therefore, hexa‐iodo‐HPB 12 was prepared and oxidized to the HBC derivative 13 . Then, HBC 13 was reacted with the boronic ester porphyrin 14 ⋅ Zn in a six‐fold Suzuki reaction to the desired product 11 .…”

A new two-dimensional metal–organic framework with high spin-filtering efficiency

“…[2][3][4][5][6][7][8][9][10][11] These 2-D materials have a wide range of applications such as high on/off ratio in field effect transistors, large rectification ratio in negative differential resistance, huge spin filtering efficiency, topologically insulating behavior etc. Graphene 1 is one of the most promising 2-D materials for future generation electronics because of its attractive properties such as quantum hall effect, high thermal conductivity, remarkable electron mobility etc.…”