Hierarchical Organization of Photoresponsive Hydrogen-Bonded Rosettes

Abstract

Hydrogen-bonded disk-shaped aggregates (rosettes) composed of azobenzene-appended melamine and barbiturate or cyanurate are investigated in view of their hierarchical organization and photoresponsive behavior by (1)H NMR and UV/vis spectroscopies, dynamic light scattering, and gelation behavior in aliphatic solvents and liquid crystalline behavior in bulk state. In the bulk state the rosette possessing a sterically bulky tridodecyloxyphenyl substituent in the barbiturate component stacks in an offset arrangement to form a rectangular columnar mesophase, whereas in aliphatic solvents it does not hierarchically organize into higher-order columnar aggregates. This drawback is improved by exchanging the barbiturate component into a more sterically nondemanding N-dodecylcyanurate component. The resulting new rosette stacks in a face-to-face arrangement to form a hexagonal columnar mesophase in the bulk state and hierarchically organizes into elongated fibrous aggregates in cyclohexane, which eventually leads to the formation of organogel. Dynamic light scattering and UV-vis experiments upon UV-irradiation of the columnar aggregates in cyclohexane revealed that the dissociation and the reformation of columnar aggregates can be controlled by the trans-cis isomerization of the azobenzene moiety. Molecular modeling indicates that the rosette possessing cis-azobenzene side chains loses its planarity. Using this photoinduced morphological change of the rosette, photoresponsive organogel is created by the use of a disk-shaped supramolecule the first time.

Gels with sense: supramolecular materials that respond to heat, light and sound

“…However, it is also possible for new, smaller assemblies to be generated, as illustrated by Yagai et al in a study of the melamine derivative 13. 255 In cyclohexane solutions, the molecule in its trans form co-assembles with a substituted barbiturate to form columnar stacks of rosette-like structures, but UV irradiation causes these to decompose into single rosettes, with trans-to-cis conversions of just 16% giving rise to a 50% decrease in aggregate size (Fig. 19).…”

Perylene bisimide organogels formed by melamine·cyanurate/barbiturate hydrogen-bonded tapes

“…16,17 As a reliable tool to control the self-assembly of functional dye molecules, we have effectively employed complementary multiple hydrogen bonding interactions between melamine and cyanurate or barbiturate. 20,21 Proper molecular design leads to the formation of well-defined hydrogen-bonded species, such as cyclic hexamers so called rosettes, 22 3 þ 1 discotics, 17,23 1 þ 1 24 or 2 þ 2 closed species, 25 rigid 26 or flexible supramolecular polymers 6,11,12,27 and so on, as the lowest level of their organization. Such hydrogen-bonded species can hierarchically organize into higher order aggregates through p-p stacking interactions of dye components.…”

Manifestation of a Chiral Smectic C Phase in Diphenylbutadiene‐Cored Bolaamphiphilic Sugars

“…[1,4] Nevertheless, the design of new molecules forming liquid crystalline phases continues to attract enormous attention, in recognition of the fact that the vast potential of this class of materials still remains untapped. [5][6][7][8] Moreover from a fundamental point of view, large gaps exist in the understanding of structure-property relationships, especially with respect to molecules containing more than one mesogenic unit. [9] Among the various liquid crystal phases, chiral nematic [1,10] and chiral smectic C (SmC Ã ) [1,10] attract considerable attention, since their potential for application in display devices is next only to nematics, which are well known for their applications in flat panel LCDs.…”