Photoactive guests

Much of the impetus for the study of hydrogen bonded network structures of 24 and bipy or other linear N-donor ligands has come from the desire to perform time-resolved crystallographic studies of photoactive guest species embedded within the network as a guest [58,62,63]. Embedding a photoactive species within a network structure effectively dilutes it in the solid state. The advantages of this include improved uniformity of illumination of the crystal, less photons are... 

Photophysical and photochemical studies of CD inclusion complexes can be divided into two categories — those in which attention is focused on the investigation of the excited-state deactivation pathways of the guest in the peculiar cavity medium, and those in which photoactive guests are used as probes to investigate the properties of the CD microenvironment. Whatever the approach, the photochemical behavior of CD-containing systems is intrinsically complex. 

Figure 9. (a) Schematic representation of the five-module format of a photoactive triad which is switchable only by the simultaneous presence of a pair of ions. This design involves the multiple application of the ideas in Figure 1. The four distinct situations are shown. Note that the presence of each guest ion in its selective receptor only suppresses that particular electron transfer path. The mutually exclusive selectivity of each receptor is symbolized by the different hole sizes. All electron transfer activity ceases when both guest ions have been received by the appropriate receptors. The case is an AND logic gate at the molecular scale. While this uses only two ionic inputs, the principle established here should be extensible to accommodate three inputs or more, (b) An example illustrating the principles of part (a) from an extension of the aminomethyl aromatic family. The case shown applies to the situation (iv) in part (a) where both receptors are occupied. It is only then that luminescence is switched "on". Protons and sodium ions are the relevant ionic inputs.

Fig. 5.8 Quen ching of the fluorescence of the dendrimer host in the presence of eosin (as guest) by energy transfer starting from the photoactive dansyl groups. The guest...

Synthetic chemists have applied the concepts of multivalency and cooperativity to supramolecular chemistry to create, for instance, biomimetic receptors able to recognize small molecules (29,30), polysaccharides (31), and DNA (32). Most of these systems are based on calixa[n]arenes (33-35), cucurbituril (CB) (36,37), and cyclodextrine (CD) (38-40) (see Fig. 1), and they represent ideal guests for assembling photoactive species. 

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