Host/guest energy transfer

Holmes R J, Forrest S R, Tung Y J, Kwong R C, Brown J J, Garon S and Thompson M E, Blue organic electrophosphorescence using exothermic host-guest energy transfer, Appl. 

The experimental results tell us otherwise. Basically, two types of study of this matter have been performed. The first of these Involves doping the crystal with a suitable guest. Host-to-guest energy transfer would be evidenced by the appearance of sensitized emission of the guest (if emissive) and by quenching of the emission of the host. If the excimer state is mobile, its lifetime should be reduced by quenching substances. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

In host-guest systems based on electron donor/ acceptor interactions, association/dissociation can be driven by redox processes so that it is possible to design electrochemical switches than can be used to control energy- and electron-transfer processes. 

Host) (Guest) Poor energy transfer Efficient energy transfer... 

I. Tanaka, Y. Tabata, and S. Tokito, Energy-transfer and light-emission mechanism of blue phosphorescent molecules in guest-host systems, Chem. Phys. Lett., 400 86-89 (2004). 

Another major energy transfer process, the so-called Forster transfer mechanism is based on a dipole-dipole interaction between the host excited state and the guest ground state (Figure 4.2) [24], It does not include the transfer of electrons and may occur over significantly larger distances. The rate constant of the Forster energy transfer is inversely proportional to the sixth power of the distance R between the molecules ... 

Moreover, these dendrimers proved to be good hosts for anionic dye molecules. Films prepared from these host-guest complexes showed efficient ( > 90%) energy transfer from the OPV units to the encapsulated dye molecules... 

Excitation energy transfer in dendritic host-guest donor-acceptor systems. Chem Phys Chem 3 1005-1013... 

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