Solid-State Structures of Phenyleneethynylenes:  Comparison of Monomers and Polymers

Abstract

The solid-state structures of a series of 2,5-dialkyl-substituted poly(p-phenyleneethynylene)s (PPEs 4, R = hexyl, dodecyl, isopentyl, ethylbutyl, ethylhexyl, H) and of 2,5-didodecyl(1,4-phenylenebutadiynylene) were investigated by X-ray powder and electron diffraction. In addition, X-ray single-crystal structures of the monomeric (1,4-dipropynyl-2,5-dialkyl)benzenes were obtained and compared to the structures of the corresponding polymers. In the case of the ethylhexyl-substituted PPE, the packing of the monomer resembles that of the polymer in the solid state. All of the examined PPEs show lamellar morphologies, in which the extended geometry of the side chains determines the value of the lamellar spacing obtained by powder diffraction. A second d value, which could be obtained for all samples represents the π−π-stacking distance of the main chains. This distance is around 3.8 Å, a typical value for stacking of aromatic systems. It implies strong electronic interaction of the chromophoric backbones, leading to the observed sharp aggregate band in CHCl3/MeOH solutions and in thin films. From the scattering data, staggered packing of the benzene rings and the phenyleneethynylene main chains in PPEs 4 was inferred. This packing avoids repulsive electrostatic interactions between adjacent conjugated phenyleneethynylene chains and at the same time leads to optimal packing of the side chains.

Poly(aryleneethynylene)s

“…Surprising are the thin and long nanoscale filamentous features that give testimony to the self-assembly processes. [84] It is not clear what determines the relatively uniform width of around 30 nm of these fibrils. Dialkyl-PPEs are ordered, crystalline, undecomposed meltable materials that display significant thermochromic effects.…”

Nine-ring angular fused biscarbazoloanthracene displaying a solid state based excimer emission suitable for OLED application

“…Because the stereocenters of the 2--ethylhexyl groups are far apart from each other, the signals observed on NMR spectra from those diastereoisomers are isochronous. 19 Quantum chemical calculations allowed the prediction of the geometry of 3 including characterisation of the molecular conformation and bond lengths. In these studies 3 was modelled with methyl groups replacing the two 2--ethylhexyl and two n--dodecyl groups for simplicity and to keep computational time reasonable (Fig.…”

The ADIMET Reaction: Synthesis and Properties of Poly(dialkyl para phenyleneethynylene)s

“…This is a refined version of the models suggested by Wrighton [43] and by Le Moigne [42]. Dialkyl-PPEs 12 form a doubly lamellar structure in the solid state [48]. The optimum space filling of the long alkyl chains forces the PPE backbone into planarity, and enables the packing of their backbones on top of one another.…”

“…Fortunately, this is not the case, and a series of different propynylated aromatics underwent ADIMET to give the polymers 48, 49, and 51-53 in good to excellent yields with respectable P n values [32][33][34][35]. Most of these polymers were not known (49,52,53) or had never been appropriately characterized (48,51). The PPVEs 52 are hybrids of PPEs and PPVs that have not been described previously.…”