How did you get interested in this research project?

I got interested in this project by reading the literature, especially the works of the Japanese researchers Ueno on the one hand, and Hamada on the other hand, and their colleagues. I envisioned that very short connections linking the pyrenyl chromophores to the b-cyclodextrin (b-CDX) backbone would make the transduction of the interaction of the b-CDX with its environment (solvent or potential host) into the fluorescence signal particularly efficient, simply by a mechanical effect (deformation of the cyclodextrin backbone). Actually the system published (compound 1) was not the one originally envisaged, as the reporters are not true b-CDXs, but systems in which the hydroxyl groups are protected with benzyl functions. 

What is the most important result in the paper?

The most important result is the dual fluorescence, be it triggered by solvent composition (Figure 1) or addition of an analyte. However, a complete understanding of this phenomenon will require further studies, as it seems that it cannot be explained by simple models. For example, the data obtained by titration of the receptor with heptanoic acid cannot be simulated by using the model of a 1:1 or 1:2 inclusion complex. It is likely that large molecular assemblies or aggregates are involved, and a further step will be the study and characterization of the latter, using light scattering and optical microscopy techniques.

Chart 1.The bis(pyrene)-functionalised b-cyclodextrin used in this study. 

  Figure 1.Fluorescence spectra of 1 at various concentrations of water in DMSO solution. The inset shows the intensity changes at 4 different wavelengths.   

What are the implications of the results you present in this paper?   

The results presented in this paper show that an in-depth understanding of the interactions and mechanisms at the supramolecular level are imperative, and that simple models that neglect to take into account the molecular environment fail to account for the phenomena observed. The study and unravelling of complex molecular assemblies formed from amphiphilic molecules is a developing area of contemporary (supra)molecular chemistry, which requires techniques that were not traditionally used by chemists (microscopy), and the further development of existing ones (DOSY NMR for example).

Are there any particular challenges facing future research in this area?       

Future research on this topic will be faced with the elucidation of the intimate mechanisms of dual fluorescence. Another interesting task will be to synthesize the initially planned bis(pyrenyl) b-cyclodextrin, a multistep process, and compare its properties with those of the system reported here. More generally, molecular detection is a topic of current interest and one challenge is to develop universal sensors, in which the molecular recognition and the signaling functions are decoupled from each other. In other words, a unique sensor (S) could detect any kind of analyte (A) by using its association (by supramolecular interactions) with a specific receptor R_A of A, so that SÉ(R_AÉA. In this way, the sensor S would respond to the substance A only, provided that the receptor R_A is present. Cyclodextrins functionalised with the appropriate fluorophore (in the case of detection by fluorescence) would be ideal candidates as sensors S. This strategy would simply require the development of non-fluorescent receptors R_A of A that include a component able to interact with the cyclodextrin cavity.   

Reference   

"Dual emission of a bis(pyrene)-functionalized, perbenzylated beta-cyclodextrin" by Cheng Huo, Jean-Claude Chambron, Michel Meyer, New J. Chem., 2008, 32, DOI: 10.1039/b803144d