Control of Luminescence Properties in Naphthalene Diimide-Based Gel with Azodibenzoic Acid by Charge Transfer Interaction

Abstract

In recent years, the self-assembly of various organic π-systems, mediated by non-covalent bonding, have been topics of considerable interest.1 These compounds that can undergo gelation hold great promise as building blocks for materials that can be applied in the construction of optoelectronic devices.2,3 The self-sorting between aromatic compounds that can serve as electron donors and electron acceptors allows the formation of distinct p-and n-type bundles of fibers that further intermix and generate multiple junction points for efficient electron transfer and transport of the charge carriers. However, a difficulty associated with simple mixing of such compounds is the possibility of a different mode of assembly, i.e., charge-transfer interaction mediated by alternate donor-acceptor stacking. Thus, examples related to self-sorting among donor-acceptor chromophores have been limited. 4 Recently, Ghosh and colleagues has demonstrated a hydrogen-bonding mediated self-assembly, 5-9 in a mixture of bis-amide-functionalized naphthalene-diimide and dialkoxy-naphthalene, where mutual recognition between similar chromophores took place to maximize the effect of hydrogen-bonding.Naphthalene-diimide derivatives have been extensively explored as building blocks for the generation of various supramolecularly assembled systems in organic-or aqueous media, because of their n-type semiconductivity, propensity for π-stacking and electron-accepting nature.9-12 Examples of such systems include organogels, catenanes, rotaxanes, foldamers, nano-tubes, hydrogels, nanoparticles, supramolecular photosystems and synthetic ion channels. 13-16To date, the literature contains little information regarding the photoluminescence properties of hydrogels, including switching of the emission color, field emission and light emitting properties. 5,9 In view of the high photoluminescence quantum efficiencies of naphthalene diimide derivatives used as fluorescent dyes, 5,17 we expected such compounds to exhibit interesting photoluminescence properties by charge transfer interaction with guest molecules. Herein, we report the formation of a hydrogel of naphthalene-diimide (1) with 4,4'-azodibenzoic acid (2). The luminescence properties were controlled by the addition of 2. Furthermore, the life-times of hydrogels were enhanced by the charge-transfer interactions.The gel based on 1 was prepared by dissolving 1% (by weight) of 1 in water. To this solution a small volume of 2 as an additive in water was added in concentrations varying from 0.2-1.0 equivalents with respect to the gelator 1 concentration. The samples were then left to stand for a week. As shown in Fig. S1, 1 could be gelated in the presence of 0-0.6 equivalent of 2, but 1 could not gelate when the amount of added 2 exceeded 0.7 equivalent. These gels prepared from a mixture of 1 and 2 exhibited a strong emission with a variety of colors under UV irradiation, in which the emission colors were dependent on the concentration of 2.The luminescent spectra of hydrogel 1 with varying concentrat...

Functional Naphthalene Diimides: Synthesis, Properties, and Applications

“…The Jung group reported the gelation of NDI:4,4′-azodibenzoic acid, resulting in control of the luminescence properties by varying their ratio and the enhancement of the hydrogel lifetimes by CT interactions. These hydrogels showed nanosecond-scale emission decays, in which the emission lifetimes were dependent on the concentration of the azo -dibenzoic acid …”

“…These hydrogels showed nanosecond-scale emission decays, in which the emission lifetimes were dependent on the concentration of the azo-dibenzoic acid. 225…”

“…In 1987, Nobel laureate Jean-Marie Lehn reported a cyclophane bearing two NDI units linked by two alkyl chains (224), followed by recognition of its molecular properties with nitrobenzene (Figure 52 (A)). 319 Thereafter, many examples of foldamers (225,226), catenanes (226), rotaxanes (227,225), and ion-channels (196), based on NDI (acceptor) and DAN (donor), via CT complexes through face-to-face aromatic interactions, were reported (Figure 52 (B)). 53,198,199,320− 322 Catenane-or rotaxane-forming strategies have employed "clipping" or "threading" methods in order to produce novel redox-active mechanically interlocked structures.…”

Chiral Supramolecular Gels with Lanthanide Ions: Correlation between Luminescence and Helical Pitch

“…On the other hand, the luminescence lifetime of gel-1 was found to be 1.75 ns (Table S2), which was similar to soft nanomaterials reported in the literature. 61,62 Thus, the blue emission of gel-1 was originated from the aggregation species of 1 as observed by fluorescence spectroscopy.…”