Nanoscale π-conjugated ladders

It is challenging to increase the rigidity of a macromolecule while maintaining solubility. Established strategies rely on templating by dendrons, or by encapsulation in macrocycles, and exploit supramolecular arrangements with limited robustness. Covalently bonded structures have entailed intramolecular coupling of units to resemble the structure of an alternating tread ladder with rungs composed of a covalent bond. We introduce a versatile concept of rigidification in which two rigid-rod polymer chains are repeatedly covalently associated along their contour by stiff molecular connectors. This approach yields almost perfect ladder structures with two well-defined π-conjugated rails and discretely spaced nanoscale rungs, easily visualized by scanning tunnelling microscopy. The enhancement of molecular rigidity is confirmed by the fluorescence depolarization dynamics and complemented by molecular-dynamics simulations. The covalent templating of the rods leads to self-rigidification that gives rise to intramolecular electronic coupling, enhancing excitonic coherence. The molecules are characterized by unprecedented excitonic mobility, giving rise to excitonic interactions on length scales exceeding 100 nm. Such interactions lead to deterministic single-photon emission from these giant rigid macromolecules, with potential implications for energy conversion in optoelectronic devices

Synthesis of a shape-persistent macrocycle with intraannular carboxylic acid groups

The synthesis of a shape-persistent macrocycle based on the phenylene-ethynylene backbone by the intermolecular oxidative Glaser-coupling of appropriate bisacetylenes is described. The ring contains two intraannular methyl carboxylates that were hydrolyzed to give the free diacid. In order to achieve sufficient solubility it was necessary to attach additional intraannular branched alkyl groups to the ring. (C) 2003 Elsevier Ltd. All rights reserved

Plasmonic surface enhancement of dual fluorescence and phosphorescence emission from organic semiconductors: effect of exchange gap and spin–orbit coupling

Dual singlet–triplet fluorescence–phosphorescence emitting compounds demonstrate that plasmonic surface enhancement is controlled solely by the underlying oscillator strength of a transition: metal-free compounds with weak spin–orbit coupling show no enhancement in phosphorescence efficiency even though fluorescence is amplified

Synthesis of a shape-persistent macrocycle with intraannular sulfonate groups

The synthesis of a shape-persistent macrocycle with two intraannular sulfonate groups is described. The cylization step is the oxidative acetylene coupling of large phenylethynyl oligomers which are covalently connected to a template. The synthesis of the templated acetylenes at the template as well as the cyclization step give high product yields showing that the template-directed approach is superior to statistical oligocyclizations

The influence of intraannular templates on the liquid crystallinity of shape-persistent macrocycles

A series of shape-persistent phenylene–ethynylene–naphthylene–butadiynylene macrocycles with different extraannular alkyl groups and intraannular bridges is synthesized by oxidative Glaser-coupling of the appropriate precursors. The intraannular bridges serve in this case as templates that reduce the oligomerization even when the reaction is not performed under pseudo high-dilution conditions. The extraannular as well as the intraannular substituents have a strong influence on the thermal behavior of the compounds. With branched alkyl chains at the periphery, the macrocycles exhibit liquid crystalline (lc) phases when the interior is empty or when the length of the alkyl bridge is just right to cross the ring. With a longer alkyl or an oligoethylene oxide bridge no lc phase is observed, most probably because the mesogene is no longer planar

Shape-persistent macrocycles with intraannular alkyl groups: some structural limits of discotic liquid crystals with an inverted structure

The synthesis and thermal properties of new shape-persistent macrocycles of different sizes decorated with intraannular alkyl chains are described. The alkyl chain length is in all cases sufficient to cross the rings and to fill their interior completely. The investigation of the thermal behavior has shown that the smaller cycles do not exhibit thermotropic mesophases. Single crystal x-ray analysis indicates that the anisotropy in these compounds is too small to describe them as plates rather than spheres. For the larger macrocycles it is shown that longer adaptable substituents decrease the phase transition temperatures compared to previously described structures

Solvent triggering between conformational states in amphiphilic shape-persistent macrocycles

The amphiphilic shape-persistent macrocycle 1 containing four phenol-OH groups as polar side groups and four hexyloxy groups as nonpolar side groups in an adaptable arrangement was recrystallized from solvents of different polarity. X-ray crystallography reveals that the conformation of the macrocycle is solvent dependent such that in the pyridine solvate only two of the nonpolar side groups point outward while in the THF solvate all four of them point outward. Moreover, in the latter case the three-dimensional packing leads to the formation of a supramolecular channel structure with a large pore size