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Host‐Assisted Guest Self‐Assembly: Enhancement of the Dimerization of Pyronines Y and B by γ‐Cyclodextrin
Author(s) -
Bordello Jorge,
Reija Belén,
AlSoufi Wajih,
Novo Mercedes
Publication year - 2009
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200800776
Subject(s) - cyclodextrin , supramolecular chemistry , chemistry , absorption spectroscopy , stoichiometry , fluorescence , absorption (acoustics) , molecule , spectroscopy , crystallography , fluorescence spectroscopy , supramolecular assembly , equilibrium constant , photochemistry , materials science , organic chemistry , physics , quantum mechanics , composite material
Buckle up! The dimerization of small fluorescent guests is strongly enhanced in presence of a cyclodextrin host. The host cavity acts like a belt to assist the self‐assembly of guests (see picture). Small variations in the guest structure have significant influence on the stability and geometry of the aggregates.The role of small variations in the structural properties of host and guest molecules on the stoichiometry and strength of supramolecular associations is analyzed. Earlier we found that a change in substituents from pyronine B to pyronine Y has a dramatic effect on both the stability and the dynamics of the association of these guests with β‐cyclodextrin as host. Now we study the association between these two pyronines and a cyclodextrin with a bigger cavity (γ‐cyclodextrin) using UV/Vis absorption and fluorescence spectroscopy. The absorption spectra of the pyronines show complex variations with cyclodextrin concentration indicating that pyronine dimerization is strongly enhanced inside the cavity of the cyclodextrin. A full model is proposed and the equilibrium constants of the involved processes and the absorption and emission spectra of the different species are estimated. The equilibrium constants of the formation of complexed dimers are much higher than those for free dimerization or for the inclusion of a single guest. The γ‐cyclodextrin host acts like a belt to assist the guest self‐assembly. The differences in the stability of pyronine B and pyronine Y dimers are explained on the basis of their structure and geometry.