Ordered Architectures of a Soluble Hexa-peri-hexabenzocoronene−Pyrene Dyad:  Thermotropic Bulk Properties and Nanoscale Phase Segregation at Surfaces

• Published in: Journal of the American Chemical Society Vol. 125; no. 32; pp. 9734 - 9739
• Main Authors: TCHEBOTAREVA, Natalia, YIN, Xiaomin, WATSON, Mark D., SAMORì, Paolo, RABE, Jürgen P., MüLLEN, Klaus
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 13.08.2003; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Other nonelectronic properties; Physical Sciences; Physics; Science & Technology; Solid surfaces and solid-solid interfaces; Solid-fluid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); SPECTROSCOPY; INTERFACE; ALIGNMENT; COMPLEXES; X-RAY; PHTHALOCYANINES; DISCOTIC LIQUID-CRYSTALS; STM; DERIVATIVES; MOLECULES; Liquid solid interface; Phase transformations; Surface segregation; Pyrene derivatives; Thermotropic crystals; Experimental study; Condensed benzenic compound; Discotic liquid crystals; Pyrographite; Thermal properties; DSC; Monolayers
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja028609i

An alkylated hexa-peri-hexabenzocoronene with a covalently tethered pyrene unit serves as a model to study self-assembling discotic pi-system dyads both in the bulk and at a surface. Wide-angle X-ray scattering, polarized light microscopy, and differential scanning calorimetry revealed bulk self-assembly into columnar structures. Relative to a control without a tethered pyrene, the new dyad exhibits a more ordered columnar phase at room temperature but with dramatically lowered isotropization temperature, facilitating homeotropic alignment. These two features are important for processing such materials into molecular electronic devices, e.g., photovoltaic diodes. Scanning tunneling microscopy at a solution-solid interface revealed uniform nanoscale segregation of the large from the small pi-systems, leading to a well-defined two-dimensional crystalline monolayer, the likes of which may be employed in the future to study intramolecular electron transfer processes at surfaces, on the molecular scale.