Deciphering the Dynamics of Organic Nanoaggregates with AIEE Effect and Excited States: Lipophilic Benzothiadiazole Derivatives as Selective Cell Imaging Probes

Abstract

An aggregation-induced emission enhancement (AIEE) effect in fluorescent lipophilic 2,1,3-benzothiadiazole (BTD) derivatives and their organic nanoaggregates were studied. A set of techniques such as single-crystal X-ray, dynamic light scattering (DLS), electron paramagnetic resonance (EPR), UV−vis, fluorescence, and density functional theory (DFT) calculations have been used to decipher the formation/break (kinetics), properties, and dynamics of the organic nanoaggregates of three BTD small organic molecules. An in-depth study of the excited-state also revealed the preferential relaxation emissive pathways for the BTD derivatives and the dynamics associated with it. The results described herein, for the first time, explain the formation of fluorescent BTD nanoaggregate derivatives and allow for the understanding of their dynamics in solution as well as the ruling forces of both aggregation and break processes along with the involved equilibrium. One of the developed dyes could be used at a nanomolar concentration to selectively stain lipid droplets emitting an intense and bright fluorescence at the red channel. The other two BTDs could also stain lipid droplets at very low concentrations and were visualized preferentially at the blue channel.

Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal–Organic Framework Linker

“…Thus, both acetylene bonds (electron donor) and the sulfur atom (electron acceptor) are the key requirements to achieve ICT in AC-TDZ. This observation is in accordance with a previous study on similar chemical structures and highlights once more the importance of the CC in the molecular design to generate the ICT state and the subsequent aggregate formation. This behavior can be explained by the larger electronegative character of S than of C, which can influence the charge transfer directed to this atom.…”

“…It is crucial to notice the importance of how slight structural variations in the chemical structure can dramatically change the excited-state dynamics. Supported by previous examples in the literature and given the absence of the ICT in AC-BZI counterparts, we conclude that it is the presence of the highly electron-withdrawing central benzothiadiazole ring that is essential to induce ICT. , …”

Photophysical Characteristics of Polarity‐Sensitive and Lipid Droplet‐Specific Phenylbenzothiadiazoles

“…Thus, the development of fluorescent dyes that specifically stain LDs is highly valuable for the study of altered lipogenesis in cancer cell biology [24c,25] . Numerous LD‐specific fluorophores have recently been reported in the literature and several of these are benzothiadiazole derivatives [23f,26] . We reasoned that structural analogues of 1 (compounds 2–11 ) also might accumulate in intracellular LDs, and this was further investigated using pediatric neuroblastoma cells (KCN‐69n), one of the most severe and common form of cancer in children [27] .…”

Fluorescent Benzothiadiazole Derivatives as Fluorescence Imaging Dyes: A Decade of New Generation Probes

“…A series of lipophilic BTD derivatives selective for LDs with the AIEE effect was recently disclosed by our group [130] . The three BTDs ( BTD‐(CCPh) 2 , BTD‐CCPh , and BTD‐BrCCPh in Figure 9) showed a strong light‐up effect in lipophilic milieu.…”