Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2023 Jun 9;24(12):9941.
doi: 10.3390/ijms24129941.

Tunable Fluorescence via Self-Assembled Switching of AIE-Active Micelle-like Nanoaggregates

Amal Farghal Noreldein Elsyed  1 , Gah-Lai Wong  1 , Mohamed Ameen  1 , Min-Wei Wu  1 , Cheng-Chung Chang  1   2
Affiliations

Tunable Fluorescence via Self-Assembled Switching of AIE-Active Micelle-like Nanoaggregates

Amal Farghal Noreldein Elsyed et al. Int J Mol Sci. .

Abstract

Chemical structures bearing a combination of aggregation-induced emission enhancement (AIEE) and intramolecular charge transfer (ICT) properties attracted the attention of many researchers. Recently, there is an increasing demand to pose tunable AIEE and ICT fluorophores that could present their conformation changes-related emission colors by adjusting the medium polarity. In this study, we designed and synthesized a series of 4-alkoxyphenyl-substituted 1,8-naphthalic anhydride derivatives NAxC using the Suzuki coupling reaction to construct donor-acceptor (D-A)-type fluorophores with alkoxyl substituents of varying carbon chain lengths (x = 1, 2, 4, 6, 12 in NAxC). To explain the observation that molecules with longer carbon chains revealed unusual fluorescence enhancement in water, we study the optical properties and evaluate their locally excited (LE) and ICT states by solvent effects combined with Lippert-Mataga plots. Then, we explored the self-assembly abilities of these molecules in water-organic (W/O) mixed solutions and observed the morphology of its nanostructure using a fluorescence microscope and SEM. The results show that NAxC, x = 4, 6, 12 show different degrees of self-assembly behaviors and corresponding aggregation-induced emission enhancement (AIEE) progresses. At the same time, different nanostructures and corresponding spectral changes can be obtained by adjusting the water ratio in the mixed solution. That is, NAxC compounds present different transitions between LE, ICT and AIEE based on the polarity, water ratio and time changes. We designed NAxC as the structure-activity relationship (SAR) of the surfactant to demonstrate that AIEE comes from the formation of micelle-like nanoaggregates, which causes a restriction of the transfer from the LE state to the ICT state, and micelle formation results in a blue-shift in emission and enhances the intensity in the aggregate state. Among them, NA12C is most likely to form micelles and the most obvious fluorescence enhancement, which will switch over time due to the nano-aggregation transition.

Keywords: Suzuki reaction; aggregation-induced emission enhancement (AIEE); intramolecular charge transfer (ICT); locally excited (LE) state; self-assembly; structure–activity relationship (SAR).

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Synthetic rots of NAXC, X = 1, 2, 4, 6, 12; (i) R-Br, K2CO3, acetone, reflux 12 h; (ii) pinacoborane, Pd(PPh3)2Cl2, 1,4-dioxane, Et3N, N2, reflux 12 h; (iii) Pd(OAc)2/(o-tol)3P, CH3COOK, 4-bromo-1,8-naphthalic anhydride, 1,4-dioxane, H2O, N2, reflux 24 h.
Figure 1
Figure 1
(a) Fluorescence spectra of NAXC in variable solvents (H2O, MeOH, EtOH, Acetone, DMF, DMSO, CH2Cl2, THF, EA and Toluene) in a concentration of 20 μM. (b) Photos show the gradual change in the color of NAXC in different solvents under a UV lamp (light source wavelength = 365 nm).
Figure 2
Figure 2
The absorption (a) and emission spectra (b) of NAXC (20 μM) in H2O. Fluorescence microscope images of NA2C (c), NA4C (d), NA6C (e) and NA12C (f) in H2O; the scale bar is 2.0 μm.
Figure 3
Figure 3
Fluorescence spectra of NAXC in ethanol were recorded at the temperature range of ~200 K (solid line) and ~300 K (dash line). Insets show the relative photos for the emission color LE and ICT states.
Figure 4
Figure 4
(a) The fluorescence spectra of NAXC in a mixture of DMF/H2O in a concentration of 20 μM; (b) the relation between the water fractions, fluorescence wavelength (black), fluorescence intensity (blue) and polarity for 20 μM of compounds NAXC in different proportions of DMF/H2O.
Figure 5
Figure 5
(a) Photographs of 20 μM NA12C in DMF/H2O mixed solvents over time. (Excitation wavelength of hand-held UV lamp: λex = 360 nm.) (b) The relative absorption and fluorescence spectra from (a,c) showed the reversible color changing of NA12C by adding and removing H2O (40% DMF/60% H2O). Fluorescence microscope images of NA12C after mixing for (d) 1 min and (e) 2 h. (Scale bar is 2 μm.) (f) SEM images of (e) (scale bar is 1 μm).
Figure 6
Figure 6
A micelle-like nanoaggregate model illustrating the transitions of LE ⇄ ICT ⇄ AIEE based on the polarity, water ratio and time changes.
See this image and copyright information in PMC

References

    1. Olsen S. Locally-Excited (LE) versus Charge-Transfer (CT) Excited State Competition in a Series of Para-Substituted Neutral Green Fluorescent Protein (GFP) Chromophore Models. J. Phys. Chem. B. 2015;119:2566–2575. doi: 10.1021/jp508723d. - DOI - PubMed
    1. Sirbu D., Butcher J.B., Waddell P.G., Andras P., Benniston A.C. Locally Excited State–Charge Transfer State Coupled Dyes as Optically Responsive Neuron Firing Probes. Eur. J. Chem. 2017;23:14639–14649. doi: 10.1002/chem.201703366. - DOI - PubMed
    1. Hong Y., Lam J.W.Y., Tang B.Z. Aggregation-induced emission: Phenomenon, mechanism and applications. Chem. Comm. 2009;14:4332–4353. doi: 10.1039/b904665h. - DOI - PubMed
    1. Wang Y., Liu H., Chen Z., Pu S. Aggregation-induced emission enhancement (AIEE)-active tetraphenylethene (TPE)-based chemosensor for CN−. SAA Mol. Biomol. Spectrosc. 2021;245:118928. doi: 10.1016/j.saa.2020.118928. - DOI - PubMed
    1. Fang H., Shi R., Chen D., Qu Y., Wu Q., Yang X., Lu X., Zhang C.-W., Li L., Lim K.-L. Intramolecular charge transfer enhancing strategy based MAO-A specific two-photon fluorescent probes for glioma cell/tissue imaging. Chem. Comm. 2021;57:11260–11263. doi: 10.1039/D1CC04744B. - DOI - PubMed

LinkOut - more resources