Hydrogen-Bonding Assisted Self-Assembly of Lamello-Columnar Phases from Discotic Supermolecules

Lei Zhu (University of Connecticut) DMR 0348724

Hydrogen-bonding is one of non-covalent interactions for molecular recognition and self-assembly in biological materials. Design of smart molecules that can self-assemble into supramolecular structures via hydrogen-bonding has been challenging to understand and mimic biological processes. On the other hand, separation of n- and p-type organic semiconductors such as discotic and cyclic molecules into distinct microdomains will enable molecular heterojunctions for photovoltaic applications.

In this work, we have attached four electron-rich triphenylene to an electron-deficient porphine through amide bonds. Instead of forming hexagonal columnar phase, hydrogen bonding at four corners of a porphine molecule induced lamello-columnar phases (see Figure 1). By tuning the arm lengths in the triphenylene and spacer lengths between triphenylene and porphine, the physical property of these liquid crystalline/crystalline structures can be controlled. Intriguingly, a simple exchange of the amide bonds to ester bonds destroyed the self-assembly in these supermolecules. This proves that hydrogen-bonding plays an important role in the self-assembly.

Through this study, we have understood the unique role of hydrogen-bonding in molecular self-assembly. This may provide us a guideline to design better organic photovoltaics.

Related Publications:1. Cui, L.; Zhu, L. Liq. Cryst. 2006, 33, 811-818.2. Miao, J.; Zhu, L. Manuscript in preparation.

Figure 1. (top) X-ray diffraction profiles of different porphine-(triphenylene)4 supermolecules linked by amide bonds (see the chemical structure watermark). (bottom) Crystalline structure of the hydrogen-bonding assisted self-assembly of lamello-columnar phases. Arms in triphenylene and spacers are omitted for clarity.

Education and Research at All Levels: Ph.D. students: Jianjun Miao (5th yr) and Weiqiang Cao (2nd yr) Two ChE undergraduate students: Nathan Barlow and Jennifer Lucatino Two REU students: Nathan Barlow and Christine Ricci (Smith College) Outreach to Undergraduate Institutions Give a lecture on nanostructured polymeric materials at Sacred Heart University.

UConn-CAS Symposium on Polymer Physics and International Collaborations A one-day symposium on Polymer Physics was held at UConn in 2007. Nine (9) participants from Chinese Academy of Science (CA) and six (6) participants attend this symposium at UConn. The topics covered a broad range of polymer physics including polyolefins, nanocomposites, and polymer dynamics. An international collaboration is started between the PI and Prof. Charles Han.

Hydrogen-Bonding Assisted Self-Assembly of Lamello-Columnar Phases from Discotic Supermolecules

Lei Zhu (University of Connecticut) DMR 0348724

Figure 2. 2008 REU students, Nathan Barlow and Christine Ricci with Prof. Zhu in front of the lab.

REU Program in Summer 2008• Christine works on synthesis, characterization and self-assembly of discotic molecules. She synthesized ionic groups containing discotic triphenylene and porphine molecules and studied their complexes.• Nate works on chemical modification of POSS molecules with various functional groups. One purpose is to couple with discotic liquid crystals.