No abstract

The elegance and efficiency by which Nature harvests solar energy has been a source of inspiration for chemists to mimic such process with synthetic molecular and supramolecular systems. The insights gained over the years from these studies have contributed immensely to the development of advanced materials useful for organic based electronic and photonic devices. Energy transfer, being a key process in many of these devices, has been extensively studied in recent years. A major requirement for efficient energy transfer process is the proper arrangement of donors and acceptors in a few nanometers in length scale. A practical approach to this is the controlled self-assembly and gelation of chromophore based molecular systems. The present tutorial review describes the recent developments in the design of chromophore based organogels and their use as supramolecular scaffolds for excitation energy transfer studies.

This Account is focused on the self-assembly of p-phenylenevinylenes, a linear pi-system, which has been extensively studied over the years due to both fundamental and technological importance. A serendipitous observation of the gelation of an oligo( p-phenylenevinylene) (OPV) derivative in nonpolar hydrocarbon solvents that led to a new class of functional materials, namely, pi-organogels, is described. Strategies to control the size, shape, and functions of the supramolecular architectures of OPV self-assemblies are highlighted. Formation of nano- to microsized helical architectures, control on chromophore packing, self-assembly induced modulation of optical properties, and application as light-harvesting assemblies are the important features of this novel class of photonically and electronically active soft materials.

White-light-emitting organic materials have attracted much attention because of their potential applications in display and lighting devices.[1] An ideal white-light-emitting system needs to emit the three primary RGB (red, green, and blue) colors in required intensities that cover the visible wavelength range from 400 to 700 nm. One of the most exploited strategies for this purpose is the use of physically blended multicomponent systems that simultaneously emit at the RGB wavelength region. In many cases, partial energy transfer between donor-acceptor molecules has been exploited for the generation of white light. Different types of materials based on p-conjugated polymers, metal complexes, and low-molecular-weight organic molecules have been used for white-light emission, either in solution or in the solid state.[2-4] However, to date, a white-light-emitting organogel has not been reported, although organogelators with tunable emission properties are known. [5][6][7] Chromophore-based selfassemblies and gels are efficient scaffolds for the design of supramolecular light,harvesting assemblies. [8,9] As a result of efficient excitation-energy migration, energy transfer in oligo( pphenylenevinylene)s (OPV) self-assemblies and gels occurs even to distantly located acceptors, present in small quantities through funnelling of excitation energy. [10,11] Herein, we report a rational strategy to the design of a hitherto unknown white-light-emitting organogel using a novel concept of functional-group-controlled donor self-assembly and consequent modulation of excited-state properties in the supramolecular gel state.The motivation for the present study stems from our recent observation of a temperature-dependent emission color change from a red gel to a blue solution through the formation of an intermediate white-light-emitting solution.[11d] However, we were not able to obtain a white-light-emitting gel in this case, since, in the gel state, the emission changes to red. Therefore, we took it as a challenge to design a white-light-emitting organogel that is successfully materialized and reported in the present study. From our experience, it is clear that control of the self-organization of the donor is crucial for energy migration, which in turn will regulate the energy-transfer processes either partially or completely, leading to tunable emission colors. In the event of a moderate self-assembly and partial energy transfer of a blue-light-emitting donor to a red-light-emitting acceptor, a mixture of blue, green, and red emissions could be simultaneously generated, leading to a white-light-emitting gel. On the other hand, in the case of a strong self-assembly and complete energy transfer, only red emission of the acceptor will occur. As a proof-of-principle of this hypothesis, we illustrate controlled energy transfer in bis-and monocholesterol-appended OPV derivatives, 1 and 2, in the presence of an acceptor 3, to result in white and red emissions, respectively (see Fig. 1). Moreover, we illustrate here how important funct...

Genaues Einstellen der Reaktivität von Glycosyldonoren und ‐akzeptoren ermöglichte die konvergente und stereoselektive Synthese von Tetra‐ und Hexasaccharidfragmenten (siehe Struktur) der B‐Kette von Rhamnogalacturonan II (RGII). Die Konformation des zentralen Arabinopyranosylrings (rot) erwies sich als abhängig vom Saccharidsubstitutionsmuster. Dieses konformative Epitop beeinflusst möglicherweise die biologischen Funktionen von RGII.