Multichromophoric Cyclodextrins. 4. Light Conversion by Antenna Effect

Abstract

A water soluble β-cyclodextrin (CD-NA) bearing seven naphthoyl chromophores forms very stable 1:1 complexes with a merocyanine laser dye DCM-OH (4-(dicyanomethylene)-2-methyl-6-(p-(bis(hydroxyethyl)amino)styryl)-4H-pyran). The antenna effect, i.e. energy transfer from the naphthoyl antenna chromomophores to the encased dye, is shown to occur with 100% efficiency. The stability of the complexes is very high (K s ≈ 105) owing to the contribution of the naphthoate residues. The structural features of the complexes have been examined in detail: circular dichroism experiments confirm the expected axial orientation of DCM-OH in the cavity of CD-NA, and fluorescence anisotropy measurements together with 13C-NMR longitudinal relaxation time measurements show that the complex formed between CD-NA and DCM-OH is tight. The mechanisms of homotransfer (i.e., between naphthoate chromophores) and heterotransfer (i.e., from naphthoate chromophores to DCM-OH included in the cavity) are discussed in light of existing theories. In both cases, the major contribution arises more likely from Coulombic interaction than from short-range interactions. Such multichromophoric cyclodextrins are good models for mimicry of the antenna function in photosynthesis and show great promise as photochemical microreactors.

Photophysical and Structural Features of Inclusion Complexes with Fluorescent Dyes

“…Inclusion of an energy acceptor in the cavity leads to a supramolecular complex in which the antenna effect, that is energy transfer from the appended antenna chromophores to the encased acceptor, can be thoroughly studied. [4,6] The circular arrangement of the antenna chromophores is reminiscent of the antenna system of photosynthetic bacteria [11] which further emphasizes the interest of multichromophoric cyclodextrins. Another outstanding feature is the capability of antennainduced photoreactions within the cavity; specific effects are indeed expected from selective excitation of the reactants included in the cavity through energy transfer from the appended chromophores.…”

“…[9] In our previous work devoted to the antenna effect in an inclusion complex of a water-soluble b-cyclodextrin CD-NA with a merocyanine (DCMOH) (Figure 1) we observed an excimer emission from the appended chromophores. [6] Later on, investigation of the complexation of several cationic surfactants [9] suggested that the excimer formation in CD-NA is likely to result from a head-to-tail interaction between two naphthalene units located on opposite sides of the functionalized primary rim. For a thorough study of the antenna effect, excimer formation should be avoided because excimers act as energy traps in the excitation energy hopping process, and energy transfer to an acceptor included in the cavity can occur from both monomer and excimer forms of the antenna chromophores.…”

“…In particular, special attention will be paid to the structure of these complexes since they turned out to be very different from the inclusion complex of DCMOH with CD-NA. [6] This investigation is a prerequisite to a detailed study of the dynamics of the antenna effect to be published later on.…”

252Cf plasma desorption mass spectrometric study of the inclusion complexes of cyclodextrins with coumarins

“…In view of the enormous research interest in such host-guest systems over the last decade, a great variety of possible guests and cyclodextrin derivatives has been studied for a number of applications. 6,7 Derivatives of 7-amino-4-methylcoumarins are widely known as highly efficient laser dyes. However, an interest in obtaining water soluble complexes of cyclodxtrins with laser dyes, to improve their spectral luminescent and generating characteristics for subsequent phototechnological application, has appeared only recently.…”

“…8 Until now such systems were mainly studied by fluorescent techniques. [7][8][9] This paper deals with the formation of complexes of cyclodextrins ( -and γ-CD) with 7-amino-4-methylcoumarin (COU120) and 7-N,N-diethylamino-4-methylcoumarin (COU1), and investigation of the capabilities of PDMS in the study of such complex formation.…”