We have synthesized a push-pull 4,4'-bipyridine containing azobenzene dye and we have prepared its stoppered inclusion complexes (rotaxanes) with α and β cyclodextrin. (The inclusion complexes formation has been varified using various spectroscopic techniques).
Surprisingly, in the UV/Vis spectra of the rotaxanes, the molar extinction coefficient of the azo π-π* band increases (it gets even 50000 1/(M.cm) that is almost double as compared to the cyclodextrin-free dye. I cannot find any information which could explain this behavior, therefore I would be glad to read your opinion.
May be you have some kind of pi-pi interaction or aggregation formation that can occur inside the CD.
Ahmed, thank you very much for your answer. Actually that makes a lot of sence. Especially because the "axial" part of these rotaxanes contains 4,4'-bipyridine in conjugation with the azobenzene unit. (Of course these rotaxanes with either α- or β-CD were isolated as [2]rotaxanes. But this should be an in solution effect).
Beside the solvent effect , you may also check the emission quantum yield at the excitation of these pi-pi interactions
long back I remember having come across a paper on the formation of pyrene dimers in some mesoporous zeolite sieves. The authors had reported some kind of a concentration dependence in this case. & also manipulation of the pore size. Higher pyrene concentration & bigger pore size allowed dimer formation readily. They could also systematically plot these dependencies. I'm sorry I don't remember the reference now.
It is due toa kind of pi-pi interaction and accumulation that happens with cyclodextrin
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