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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.
Journal of the American Chemical Society 04/2012; 134(18):7983-94. · 9.91 Impact Factor
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ABSTRACT: Discotic supramolecular complexes bearing six perylene bisimide (PBI) chromophores were prepared by mixing monotopically triple-hydrogen-bonding melamines equipped with two PBI chromophores and two 3,7-dimethyloctyl chiral handles with tritopically triple-hydrogen-bonding cyanuric acid (CA). UV/Vis and fluorescence titration experiments demonstrated that the discotic complexes were formed in methylcyclohexane by the 3:1 complexation between the melamines and CA. TEM and AFM studies revealed that the complexes hierarchically organize into fibrous columnar assemblies, which eventually results in the formation of organogels. Circular dichroism (CD) and flash-photolysis time resolved microwave conductivity measurements revealed the presence of extended chiral stacks of PBI chromophores within the columns. The anisotropy factors of the columnar assemblies are remarkably high (g=1.5×10(-3)) when considering the presence of only one 3,7-dimethyloctyl chiral handle per perylene chromophore, suggesting that the columnar structures have a biased helical sense. The fact that the chiral centers are located inside the discotic complexes rather than at their peripheries might be unique structural property responsible for the rather strong optical activities for the assemblies of this chromophore. The effective transcription of the molecular chirality to the extended columnar assemblies through the formation of unique discotic complexes enables the expression of "majority-rules" chiral amplification effect, which is unprecedented for the supramolecular assemblies of PBIs.
Chemistry 03/2011; 17(13):3598-608. · 5.93 Impact Factor
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ABSTRACT: Extremely long nanofibers, whose lengths reach the millimeter regime, are generated via co-aggregation of a melamine-appended perylene bisimide semiconductor and a substituted cyanurate, both of which are ditopic triple-hydrogen-bonding building blocks; they co-aggregate in an unexpected stoichiometrically mismatched 1:2 ratio. Various microscopic and X-ray diffraction studies suggest that hydrogen-bonded polymeric chains are formed along the long axis of the nanofibers by the 1:2 complexation of the two components, which further stack along the short axis of the nanofibers. The photocarrier generation mechanism in the nanofibers is investigated by time-of-flight (TOF) experiments under electric and magnetic fields, revealing the birth and efficient recombination of singlet geminate electron-hole pairs. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements revealed intrinsic 1D electron mobilities up to 0.6 cm(2) V(-1) s(-1) within nanofibers.
Small 11/2010; 6(23):2731-40. · 8.35 Impact Factor
