Cyclodextrins antennas

Supermolecular interlocked macromolecules have been paid much attention as candidates of smart materials. Polyrotaxane (PRX) is a typical example. PEG/ cyclodextrin (CD)-based polyrotaxane was firstly reported by Harada and coworkers by attachment of stoppers to pseudopolyrotaxane (pPRX) consisting of a PEG and CDs [263]. Subsequently, many CD-based PRXs have been designed and prepared as smart materials such as biomaterials, light-harvesting antennae, insulating polymers, stimuli-responsive molecular shuttles etc. [264—268]. 

A //-cyclodextrin bearing seven 2-naphthoyloxy chromophores, CD7(6), is a good model for studying the effect of the excitation wavelength on energy hopping among chromophores in well-defined positions, as in photo synthetic antennae. 

Figure 8. Schematic representation of the cyclodextrin-based antennas [27],...

Generally speaking, an antenna for light harvesting is an organized multicomponent system in which several chro-mophoric molecular species absorb the incident light and channel the excitation energy to a common acceptor component. Artificial antenna systems based on porphyrin arrays [63], multichromophoric cyclodextrins [64], polynuclear metal complexes [65, 66], dendrimers [66-68], and polymers [69, 70] have been reported. In all these systems, the chromophoric units are connected by means of covalent... 

Parrot-Lopez, H., Leray, E., Coleman, A. W. New (3-cyclodextrin derivatives possessing biologically active saccharide antennae. Supramol. Chem. 1993, 3, 37-42. 

Cyclodextrins can be functionalized with various types of chromophores on both the primary and the secondary hydroxyl rims. A review of the prepared, selectively 0-substituted, CDs has been published [204], The modified CDs show interesting photochemical properties which have been exploited to detect photochemically inactive organic compounds in aqueous solutions [205], to induce stero- and regioselectivity in some photochemical reactions, and to mimic the energy transport from the antenna to the reaction center in the photosynthetic membrane (vide infra). 

Jullien, L, 1 CanceiU, B Valeur et al. (1996). Multichromophoric cyclodextrins. 4. Light conversion by antenna effect. Journal of the American Chemical Society, 118 (23), 5432-5442. 

Heptakis 6-0-t-butyldimethylsilyl-P-cyclodextrin, on reaction with 4-chloro-methyl-A -methyl-2-nitroaniline, affords the mono-3-substituted benzyl ether. P-Cyclodextrin carrying a 2-(naphthylmethyl) group at 0-6 exists with the aromatic rings within the cavity to an extent which is very temperature dependent. Temperature can therefore be used to control the degree of complexing of the aromatic system with a fluorescent naphthalene compound. Heptakis-[2,3-di-0-acetyl-6-deoxy-6-iodo]-P-cyclodextrin treated with 6-methoxycarbonyl-2-naphthol allowed access to the compound having naphthoic acid substituents at all of the primary positions, and this forms a very stable 1 1 complex with a merocyanine laser dye which is a mimic of the antenna function in photosynthesis and shows promise as a photochemical microreactor. Mono-[6-0-(8-qui-nolyl)]-P-cyclodextrin has been reported, and the stabilities of inclusion complexes with amino acid guests have been described. ... 

An interesting problem, arising when a large number of identical chromophores is present in an artificial antenna system, is whether excitation hopping between such units can occur in a truly chaotic fashion. This problem has recently been addressed by Valeur and co-workers using a P-cyclodextrin labeled with seven naphthoyloxy chromophores on the primary face. ... 

Lehn and co-woikers have described the antenna effect in multichromophoric cyclodextrins, where excitation energy is transferred from chromophores (attached to the c.d.) to complexed merocyanine, with an efficiency close to 1. ... 

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