Polymer-Induced Self-Assembly of Small Organic Molecules into Ultralong Microbelts with Electronic Conductivity

Abstract

The principle of polymer-controlled crystallization of inorganic materials has been successfully transferred to functional aromatic organic dyes, in this instance 3,4,9,10-perylenetetracarboxylic acid potassium salt (PTCAPS), after its single-crystal structure was determined. The cationic double hydrophilic block copolymer poly(ethylene glycol)-block-branched-poly(ethyleneimine) (PEG-b-PEI) was used as the polymer additive to modify the crystallization of PTCAPS. Ultralong hierarchically structured PTCAPS microbelts with constant width and thickness of each individual belt have been fabricated. The belts are a mesocrystalline assembly of primary nanoparticles with high-energy anionic {001} faces stabilized by polymer complexation. Polarization microscopy, X-ray diffraction, optical absorption spectra, and fluorescence spectra indicate the favorable orientation of the 1D microbelts in the close-stacking direction and reveal a specific 1D superstructure fluorescence. Electrical conductivity measurements performed on a single nanobelt disclose in the doped state a remarkably high electronic conductivity and further demonstrate extended, wirelike pi-pi interactions along the [020] long axis of the belts. Together with the very large length of the belts and their organic-organic hybrid nanostructure, this makes these organic wires potentially interesting for the field of nano-/micro-optoelectronics.

Mesocrystals and Their Related Structures as intermediates between single crystals and polycrystals

“…reported that a specific conductivity was obtained on the iso-oriented assembly of functional aromatic organic dyes. 110) A remarkably high electronic conductivity was observed on ultralong microbelts consisting of primary nanoparticles. Koumoto et al proposed that SrTiO 3 -based mesocrystals exhibit an excellent thermoelectric property due to a two-dimensional electron gas grain boundary.…”

Morphology-controlled growth of perylene derivative induced by double-hydrophilic block copolymers

“…Based on pH titration results, one carboxylic acid group was still protonated and only 3 groups in the salt form. 19 Because the solubility of PTCAPS in water is very high and it is practically insoluble in many organic media, we used a facile recrystallization method to prepare crystals of PTCAPS from ethanol/water mixed solvents. The precursor PTCAPS molecules dissolve in mixed solvents at higher temperature and precipitate as the temperature decreases because the solution is supersaturated at the lower temperature.…”

“…In fact, it was reported that perylene has both the α and β polymorphs. 16(b) The single crystal structure of the stable PTCAPS β-polymorph has been published previously, 19 while we were not able to collect a big-enough single crystal of the α-polymorph being stable long enough to determine its single crystal structure.…”

“…19 The unit cell parameters are a = 7.4228(14) Å, b = 8.1929(18) Å, c = 14.838(4) Å, α = 104.299 (18) • , β = 100.577 (18) • , γ = 95.938 (7) • . The expected equilibrium morphology as well as the growth directions is presented in Figure 3.…”

“…At pH 9.6, PEG-b-PEI is slightly positively charged (pKa of PEI 10-11) 20 and PTCAPS negatively charged. 19 Therefore, PEG-b-PEI can interact with PTCAPS by electrostatic interaction and adsorb onto the negatively charged {001} faces. This leads to blocking of these faces from further growth, as the surface energy gets lowered, and further exposition of {001} in the default morphology according to Wulffs rule 21 to yield very thin plates, which are the primary building units of the structures in Figure 4.…”