Evidence for the Cyclodextrin Mediated Aggregation of Cyanine Dyes into Oligomers |
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Authors: | Christopher Roos Volker Buss |
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Affiliation: | (1) Fachgebiet Theoretische Chemie, Gerhard-Mercator-Universität Duisburg, D-47057 Duisburg, Germany |
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Abstract: | Based on the analysis of UV/Vis-and CD spectra of several cyanine dyes in - and -cyclodextrin a case is made for the aggregation of the dyes into oligomers. The criteria for this new type of aggregates are: (i) the appearance of a concentration and temperature dependent shoulder on the high energy side of the dimer band in the UV/Vis-spectra; (ii) two oppositely signed high intensity CD absorptions, one centered at the shoulder, the other at about the energy of the monomer absorption. Calculations based on coupled-oscillator theory support the contention that chiral dye aggregates are formed in the presence of cyclodextrins, most probably trimers and tetramers. From UV/Vis- and CD-data a helically twisted sandwich structure is suggested for these aggregates. In contrast to the reported inclusion complexes these aggregates must form — at least partly — outside the chiral host. |
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Keywords: | Cyclodextrin cyanine dyes chiral aggregates circular dichroism exciton interaction |
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