Tunable Aggregation-Induced Multicolor Emission of Organic Nanoparticles by Varying the Substituent in Naphthalene Diimide

Abstract

In this article, we have designed L-aspartic acidlinked naphthalene diimide (NDI)-based amphiphilic molecules having a benzyl ester group at both the terminals with varying substituents (NAB-1−5). The substituent was judiciously modified from an electron-withdrawing group (EWG) like nitrobenzene to an electron-donating group (EDG), methoxybenzene, and finally to an extended aromatic residue (naphthalene) to regulate the π-electron density at the terminal of NDI derivatives. All of the synthesized NDI derivatives were molecularly dissolved in dimethyl sulfoxide (DMSO), and with an increase in the water content within the DMSO solution, the NDI derivative starts to get selfassembled through J-aggregation at and above 40% water content. Self-assembled spherical organic nanoparticles formed in 99% water in DMSO (f w = 99%) were characterized by microscopic studies. All of the NDI derivatives showed very weak emission in the molecularly dissolved state (DMSO). Aggregation-induced emission (AIE) was observed for the NDI derivatives (except NAB-1) at the self-assembled state through excimer formation. Upon excitation at 350 nm, the emission maxima of these NDI-based AIE luminogens (AIE-gens) (NAB-2−5) get red shifted from 463 to 588 nm upon altering the substitution from EWG to EDG at the donor site. Inclusion of proper donor−acceptor moieties in the molecular backbone of the self-assembling unit can govern the AIE in combination with the intramolecular charge-transfer process. Consequently, the emission color of these AIE-gens (NAB-2−5) gets tuned from cyan blue to faint green to strong green and finally to bright orange. The tunable aggregation-induced multicolor emission was investigated by different spectroscopic techniques. These cytocompatible, multicolor-emitting fluorescent organic nanoparticles were utilized for bioimaging applications.

Nature of the N‐Substituted Alkyl Chain Influencing Emission Properties of Naphthalene Diimide (NDI) Via Excimer, and Exciplex Formation

“…[16,17] The main challenge associated with NDI derivative is the poor optical properties [18] when modified at the imide position which limits their applications compared to a similar class of πaromatic compounds such as perylene diimide (PDI) which shows excellent quantum yield values near to unity. [19] Many of the literature reports suggest various strategies to overcome this limitation mainly by structural modification and also adapting suitable methods of self-assembly such as aggregation in the solvent mixture, [20] excimer/exiplex formation, [21,22] aggregation-induced enhanced emission (AIEE), [23] donor-acceptor (DÀ A) interactions, [24] and H-/J-type aggregate formation, [25] etc. Hence, the molecular design which defers the aggregation caused quenching (ACQ) [26] plays an important role in deciding the applications of these compounds when self-assemble from different solvents, especially from water.…”

Aggregation-induced emission enhancement (AIEE)-active boron-difluoride dyes with reversible mechanochromic fluorescence

“…But in the solid state, the rotation was restricted, therefore, they emit low or no uorescence in dilute solutions but intense uorescence in the solid state. Although a few examples of AIEE complexes ascribed to J aggregation, 36,37 excimer formation [38][39][40] have been reported, there have been limited reports on AIEE boron-diuoride dyes based on J(H)aggregate which are formed between chromophores with tight chromophore spacing and strong coupling, 41 and it is still highly signicant to explore new AIEE dyes based on boron-diuoride chromophore for developing new functional luminescent materials. On the other hand, the aggregation and deaggregation might be manipulated by external stimuli (heat, pressure and etc.)…”

Realization of multi-configurable logic gate behaviour on fluorescence switching signalling of naphthalene diimide congeners

“…23 Even though NDI shows very weak emissions, however, changing the substituents signicantly affect the optical properties of NDI. 24,25 Efforts have been made to increase the uorescence and self-organization properties by core substitution with amino groups 26 and N-substitution with highly directional H-bonding interactions via chemical modications. 27,28 Modern day research provides the opportunity to work in the multidisciplinary subjects sharing a common platform to exchange new ideas, creating new innovations to develop smart and efficient products.…”