Supramolecular Organization of α,α‘-Disubstituted Sexithiophenes

Abstract

The self-assembly of alpha,alpha'-linked sexithiophenes with chiral and achiral penta(ethylene glycol) chains attached at the alpha-positions of the terminal rings, that is, 2,2':5',2'':5'',2''':5''',2'''':5'''',2'''''-sexithiophene-5,5'''''-dicarboxylic acid-2S)-2-methyl-3,6,9,12,15-pentaoxahexadecyl ester (1) and 2,2':5',2'':5'',2''':5'''',2''''':5''''',2'''''-sexithiophene-5,5'''''-dicarboxylic acid-3,6,9,12,15-pentaoxahexadecyl ester (2), respectively is described. Analysis of the UV/vis, fluorescence, circular dichroism, and circular polarization of luminescence spectroscopic data shows that these compounds form chiral aggregates in polar solvents and in the solid state. In n-butanol aggregation occurs at temperatures below 30 degrees C, while above this threshold temperature the aggregates break up without an intermediate disordered state of aggregation, and the compounds are molecularly dissolved. The "melting temperature" of the aggregates depends on the concentration of sexithiophene, indicating that the optical changes observed are a result of intermolecular processes. Mass spectrometric measurements reveal that 1 and 2 can form mixed aggregates. Analysis of the optical spectra reveals that in these mixed aggregates, chiral 1 molecules act as "sergeants" to direct the packing of the "soldiers" 2, illustrating cooperativity within the columns. In water, the same type of chiral aggregates are formed as in n-butanol below 30 degrees C; however, these aggregates are still present, but the chirality is lost above 30 degrees C. In spin-coated films of 1 chiral aggregates are present. AFM studies show that 1 self-organizes into chiral fiberlike structures in the solid state. Furthermore both 1 and 2 display thermotropic liquid crystalline behavior between 180 and 200 degrees C.

Photostability of J ‐aggregates adsorbed on TiO2 nanoparticles and AFM imaging of J ‐aggregates on a glass surface

“…Sideon aggregation of the fibers subsequently yields supercoiled structures with left-handed helicity [17]. The above mentioned observation along with more recent reports [18], indicate that the left handiness of ropelike supramolecular assemblies appears to be a general trend, regardless of the chirality of the monomer units.…”

Supramolecular Electronic Coupling in Chiral Oligothiophene Nanostructures

“…This, in conjunction with circular dichroism effects in the supramolecular phase, has been previously assigned to the formation of chiral supramolecular structures in the sexithiophene derivative 1b. [13] We note that, in addition to the main blue-shifted absorption band, there is also a red-shifted absorption present in all three materials. It has a small but nonvanishing oscillator strength, as to be expected for not perfectly aligned face-to-face intermolecular geometry.…”

“…We investigate, by means of time-integrated and time-resolved PL spectroscopy, a series of three functionalized oligothiophenes that have been previously shown to self-assemble into chiral supramolecular stacks in semipolar solvents. [13] These further self-assemble into vesicular structures. [14] The functionalized oligothiophenes are model systems for unambiguously investigating intermolecular electronic coupling effects because the supramolecular assembly process in solution is thermotropically reversible with a well-defined transition temperature (28°C for the sexithiophene derivative at concentrations of ∼ 2.6 × 10 -5 M, with a width of approximately 20°C), allowing direct comparison of the photophysics of assembled and dissolved systems.…”

Strategies towards chiral molecular conductors

“…In the paragraph concerning supramolecular chirality we will briefly discuss the case of the nanocoils formed by hexabenzocoronene derivatives, a system in which the mobility of the charge carriers might parallel that in helical carbon nanotubes. The annelated helical -oligothiophenes have been recently reviewed by Rajca et al, 12 while formation of chiral aggregates based on sexithiophene derivatives was reported by Meijer et al 13 Chiral polyaniline assemblies have been obtained upon adding camphor sulfonic acid as chiral dopant in the polymerization process. 14 Finally, one should mention also the huge amount of work dedicated to the investigation of the supramolecular helicity in derivatives of oligo(p-phenylenevinylenes).…”