title: Supramolecularly engineered perylene bisimide assemblies exhibiting thermal transition from columnar to multilamellar structures.
abstract: Perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI) was functionalized with ditopic cyanuric acid to organize it into complex columnar architectures through the formation of hydrogen-bonded supermacrocycles (rosette) by complexing with ditopic melamines possessing solubilizing alkoxyphenyl substituents. The aggregation study in solution using UV-vis and NMR spectroscopies showed the formation of extended aggregates through hydrogen-bonding and π-π stacking interactions. The cylindrical fibrillar nanostructures were visualized by microscopic techniques (AFM, TEM), and the formation of lyotropic mesophase was confirmed by polarized optical microscopy and SEM. X-ray diffraction study revealed that a well-defined hexagonal columnar (Col(h)) structure was formed by solution-casting of fibrillar assemblies. All of these results are consistent with the formation of hydrogen-bonded PBI rosettes that spontaneously organize into the Col(h) structure. Upon heating the Col(h) structure in the bulk state, a structural transition to a highly ordered lamellar (Lam) structure was observed by variable-temperature X-ray diffraction, differential scanning calorimetry, and AFM studies. IR study showed that the rearrangement of the hydrogen-bonding motifs occurs during the structural transition. These results suggest that such a striking structural transition is aided by the reorganization in the lowest level of self-organization, i.e., the rearrangement of hydrogen-bonded motifs from rosette to linear tape. A remarkable increase in the transient photoconductivity was observed by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements upon converting the Col(h) structure to the Lam structure. Transient absorption spectroscopy revealed that electron transfer from electron-donating alkoxyphenyl groups of melamine components to electron-deficient PBI moieties takes place, resulting in a higher probability of charge carrier generation in the Lam structure compared to the Col(h) structure.
authors.affiliation: Department of Applied Chemistry & Biochemistry, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan. yagai@faculty.chiba-u.jp
authors.forename: Shiki
authors.initials: S
authors.lastname: Yagai
authors.forename: Mari
authors.initials: M
authors.lastname: Usui
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Seki
authors.forename: Haruno
authors.initials: H
authors.lastname: Murayama
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kikkawa
authors.forename: Shinobu
authors.initials: S
authors.lastname: Uemura
authors.forename: Takashi
authors.initials: T
authors.lastname: Karatsu
authors.forename: Akihide
authors.initials: A
authors.lastname: Kitamura
authors.forename: Atsushi
authors.initials: A
authors.lastname: Asano
authors.forename: Shu
authors.initials: S
authors.lastname: Seki