Structure and Property Diversity of Chiral Helicene Oligomers

Abstract

alkylthio, and perfluoroalkyl groups. In addition, cyclization of helicene oligomers provides another method of obtaining diversity.A notable aspect in the diversity of helicene oligomers is that they can be connected to provide multidomain oligomers (Fig. 4). When two helicene oligomers are connected, they are referred to herein as homo-bidomain oligomers. Cyclic homo-bidomain oligomers are also conceivable. Hetero-multidomain oligomers can be obtained by connecting different structures of oligomers. Such manipulations provide a large diversity of structures.Because helicene can generate characteristic π−π interactions, helicene oligomers often form bimolecular, trimolecular, tetramolecular, and polymolecular aggregates in which homoaggregation and heteroaggregation can also occur. Such aggregates self-assemble to form fibrils, vesicles, liquid crystals, and surface monolayers. These noncovalent bonding interactions provide diversity of the structure of helicene oligmers. Diverse Properties of Helicene OligomersStructural diversity is directly related to diversity of properties, and the properties of a helicene oligomer can be varied by structural modifications. In addition, multidomain oligomers can be designed, in which properties A and B of each domain can be combined. Such compounds exhibit property A + B or even another property C, a result regarded as the "synthesis of a property or function." Aggregation and self-assembly of helicene oligomers further increase property diversity, which covers materials with a broad range of sizes from subnanometersized molecules through nano-and micrometer-sized molecular aggregates and molecular self-assemblies to macroscopic bulk materials. Helicene oligomers are sensitive to changes in the environment such as temperature, solvent, and concentration. Different properties appear in dilute solution, in concentrated Amidohelicene oligomers: (a) acylcic oligomers (P)-1 (n = 1−9) with dianiline spacer, cyclic oligomers (P)-2 (n = 1−10) with dianiline spacer, (b) acyclic oligomers (P)-3 (n = 1−9) with m-phenylene spacer, and acyclic reverse oligomers (P)-4 (n = 1−4). (c) Schematic representation of reversible change between helix dimer and random coils of (P)-3 and (P)-4. solution, in the crystalline state, in the amorphous state, on the solid surface, at the solid-liquid interface, in fiber assemblies, in liquid crystals, and in gels. Dynamic properties of helicene oligomers are also interesting, and structural changes are largely affected by the environment, providing a stimulus response or possible molecular switching materials. It is also noteworthy that the process of a structure change can produce unusual transient phenomena. Amidohelicene OligomersStudies on helicene oligomers were initiated with amide derivatives (Fig. 5a, top), in which the spacer has a bent shape and includes both hydrogen bonding donor and acceptor moieties (24). (P)-5,8-Helicenedicarboxylate was reacted with bis(2,6-dimethylanilino)cyclohexane to give a series of acyclic helicene oligomers 1 up t...

Chemical Systems Involving Two Competitive Self-Catalytic Reactions

“…In our studies on the synthesis and function of chiral helicene derivatives of 1,12-dimethylbenzo-[c]phenanthrene, their oligomers were developed, in which the helicene is connected by m-phenylene spacers and two-atom linking groups. [43][44][45][46]86 Many such oligomers above a certain number of helicene unit formed dimeric aggregates, most likely double helices. In the series of oligomers, the number of helicenes, spacer, linking group, and side chain can be systematically varied, which provided a versatile method to develop synthetic double-helix forming compounds.…”

Synthesis and Self-Assembly of Chiral Cylindrical Molecular Complexes: Functional Heterogeneous Liquid-Solid Materials Formed by Helicene Oligomers

“…An example is self-catalysis, which is a phenomenon, in which a double-helix molecular complex catalyzes the reaction of random-coil molecules to become a double-helix. This is a molecular communication system, in which various unusual molecular events occur, such as thermal hysteresis and equilibrium crossing, which have been summarized in recent review articles [ 34 , 35 , 36 , 37 , 38 ].…”

“…Their properties have not been well examined, although many syntheses are reported [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. On the basis of a large-scale synthesis of 1,12-dimethylbenzo[ c ]phenanthrene developed in this laboratory, we have studied the synthesis and function of helical substances using helicenes as building blocks [ 34 , 35 , 36 , 37 , 38 ] Helical substances treated here range from molecules to oligomers, molecular complexes and self-assembly materials, each of which exhibited notable properties and functions.…”

Pendant-Type Helicene Oligomers with p-Phenylene Ethynylene Main Chains: Synthesis, Reversible Formation of Ladderlike Bimolecular Aggregates, and Control of Intramolecular and Intermolecular Aggregation

“…During the course of our studies on the synthesis and function of linear helicene oligomers, we synthesized ( P )-ethynylhelicene oligomers ( P )- 1 in which helicene and m -phenylene were connected by acethylene linkers (Figure ). The linear helicene oligomers formed double helices , in solution, which exhibited various responses to changes in the environment .…”