Redox-active guests

LUMOPHORE-SPACER-RECEPTOR SYSTEMS WITH REDOX ACTIVE GUESTS... 

As Figure 3 illustrates, redox active guests introduce PET processes almost by definition and luminescent on-off switching is the norm. However, the inhibitions outlined in Section 5 have not prevented the designers of switchable luminescent devices from exploring systems which bind redox active guests. The combined forces of inorganic coordination chemistry and supramolecular science have proved to be too attractive in many of these instances. It is to be hoped that some of this effort will filter across to the examination of more on-off systems like 17 and 18. 

Cu(II) is one of the best examples of a redox active guest, but apparently not when it is imprisoned in a cryptand such as 53. In this case, the Cu(II) is silent over a wide potential range during cyclic voltammetry. System 53 is designed as a lumophore-spacer-receptor system such as 28-30 and 33-34 in Section 1 with multiple lumophores. It also shows similar luminescence off-on switching with and even with Cu(II). The possibility of Cu(II) induced production of from moisture appears to have been ruled out. The absence of EET is a mystery which can only be dispelled by further studies on this interesting system. 

CYCLODEXTRIN AND CUCURBITURIL COMPLEXATION OF REDOX-ACTIVE GUESTS 71... 

Fabbrizzi s S[36] is unusual in using a nonmetallic, redox-active guest with a metal center serving as the receptor. An anionic nitrobenzoate guest is held by coordination of the carboxylate to the free apical position in Zn2+. The electron-deficient nitrobenzoate engages in PET with the anthracene fluorophore to switch the fluorescence OFF . 

When the redox active guest anthraquinone-2-carboxylic acid is added to compound 47, a partial quenching of about 20 % of the MLCT emission of the ruthenium center of the complex is observed, while no quenching is observed when the same substrate is added to the metal complex in absence of the cyclodextrin receptor. The partial quenching can be then ascribed to the occurrence of an electron transfer process between the guest complexed into the CD cavity and the appended metal center [88]. 

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