Mind the gap – Enhancing intercalation of luminescent aggregates

Particular molecules, which are not luminescent in solution, can luminesce intensely upon molecular aggregation; this is known as aggregation-induced emission (AIE). AIE luminogens are used widely as efficient electroluminescent materials, sensitive chemosensors, and as bioprobes. The main cause of the AIE effect is the restriction of intramolecular rotation. Therefore it can be promoted by introducing the molecules into inorganic materials with a rigid skeleton such as α-zirconium phosphate layers.

Jihong Yu and colleagues from Jilin University in China have published a method describing the intercalation of a quaternary tetraphenylethene (TPEN) cation, an AIE chromophore, into α-zirconium phosphate. At first glance, this does not seem to be too difficult a task– after all, the TPEN has two permanent positive charges on either end suitable to interact with the negatively charged phosphate layers. But, in this case, size does matter. The chromophore is almost three times larger than the distance between phosphate layers, more than a tight fit!

Stretching the layers of α-zirconium phosphate by preintercalation of butylamine before introduction of the chromophore

To overcome this problem, Yu and colleagues carried out a preintercalation step with butylamine before performing a cation exchange step to place the TPEN chromophore within the phosphate layers. Ultimately, they stretched the layer before putting the final molecule inside, just like you would stretch a pair of shoes in an effort to make them fit before placing your sensitive feet inside.

The intercalated product was found to be highly emissive in the blue region of the electromagnetic spectrum and was readily internalized by cells. The system also showed good biocompatibility, suggesting that it would make an excellent base for fluorescent labels in future biomedical imaging applications.

To read the details, check out the HOT Chem Comm article in full:

AIE cation functionalized layered zirconium phosphate nanoplatelets: ion-exchange intercalation and cell imaging

Dongdong Li, Chuanlong Miao, Xiaodan Wang, Xianghui Yu, Jihong Yu and Ruren Xu
Chem. Commun., 2013, 49, Accepted Manuscript
DOI: 10.1039/C3CC45041D

Iain Larmour is a guest web writer for ChemComm.  He has researched a wide variety of topics during his years in the lab including nanostructured surfaces for water repellency and developing nanoparticle systems for bioanalysis by surface enhanced optical spectroscopies.  He currently works in science management with a focus on responses to climate change.  In his spare time he enjoys reading, photography and art.

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