RGB Emission through Controlled Donor Self‐Assembly and Modulation of Excitation Energy Transfer: A Novel Strategy to White‐Light‐Emitting Organogels

Abstract

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...

Self‐Assembly of Schiff Base Organogelator with Enhanced Fluorescence Emission

“…[17] Morphology investigation by SEM (Figure 3) showed that the organogels possess a 3D network constructed from entangled bundles of fibrous aggregates. It is well known that an increase in the rigidity of a molecule can decrease molecular vibrations, probably suppress the internal conversion of an excited molecule, thus making the organogels highly emissive upon photoexcitation.…”

Fluorescence resonance energy transfer in AOT/4-chlorophenol/m-xylene organogels

“…Hence, FRET studies have been conducted in micelles [12], reverse micelles [13,14], vesicles [15], liposomes [16], ionic liquids [17,18], supramolecular assemblies [19], DNA [20], quantum dots and cyclodextrins [21], etc. Recently, there has been a spurt in energy transfer studies aimed for the development of novel white light emitting organogels like [22][23][24][25][26][27].…”

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

“…At a specific composition and temperature, partial energy transfer from the gel to the polymer resulted in white photoluminescence. [64,65] Meijer et al have functionalized three different p-conjugated oligomers 51, 52, and 53 with self-complementary quadruple hydrogen bonding ureidopyrimidinone (UPy) units at both ends ( Figure 17). The molecules self-assemble in solution and in the bulk, forming supramolecular polymers.…”