NIST - Materials Science Engineering Laboratory - Polymers Division

Polymers Main Page > Out from under the Radar > Detail

Polymers Division - Out from under the Radar

Self-Organization of Supramolecular Helical Dendrimers into Complex Electronic Materials

Measurement of material structure supports a collaborative optoelectronic material research effort

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided they exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical because they are difficult to process, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. We have shown that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic donor and acceptor moieties (e.g., Figure 1).

Figure 1. a.) Molecular structure of electron acceptor (A), whose electron mobility in the columnar rectangular phase is (2.3 ±0.4) x10-3 cm2V^-1s^-1. The mobility is approximately three times higher in the lower temperature (25°C) glassy phase.
b.) Molecular structure of an electron donor (D), whose hole mobility in the columnar hexagonal phase is (1.5 ±0.3) x10^-3.

Attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometer scale columns (Figure 2) that contain in their cores p-stacks of donors, acceptors, or donor-acceptor complexes exhibiting tight packing and high charge carrier mobilities, demonstrating the viability of synthetic supramolecular chemistry for electronic materials. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, they coassemble so that the polymer is incorporated in the centre of the columns through donor-acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive p-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications. Interfacial interactions and solidification conditions are critical for obtaining the desired alignment of columns, for effective charge transport (Figure 3).

Figure 2. The glassy-phase molecular arrangement in the supramolecular column self-assembled from molecule A.

Figure 3. Films of molecule D on hydrophobic indium-tin oxide, cooled a.) rapidly 20°C/min and b.) slowly 0.1°C/min, and viewed between crossed polarizers. The dark appearance in (b) indicates that the supramolecular columns are nearly perpendicular to the film surface.

Figures from Percec et al., Nature 419,384 (2002).

Contributors and Collaborators

V. Percec, M. Glodde, T. K. Bera, Y. Miura, V. S. K. Balagurusamy, P. A. Heiney (U. Pennsylvania); I. Shiyanovskaya, K. D. Singer (Case Western Reserve U.);
I. Schnell, A. Rapp, H.W. Speiss (Max Planck Institute for Polymer Research, Mainz, Germany).

NIST Material Science & Engineering Laboratory - Polymers Division