Aggregation Behavior of a Thermotropic Discotic Bi-4H-pyran Derivative in Solution

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Abstract
A Δ4.4′-bi-4H-pyran derivative that exhibits discotic mesomorphism of the thermotropic type was observed to self-associate in solution as well as in an ethyl cellulose polymer film at concentrations in the 10−5 M range. The aggregate structure was verified and characterized by its absorption and circular dichroism spectra. The molecular aggregate displays electronic transitions in roughly the smae spectral region as the monomeric species but with drastically different relative intensities, unlike those of J aggregates. The long-wavelength electronic transitions displayed by the aggregate are 17 times more intense than the corresponding absorption due to the monomer. The strong propensity for self-association in solution appears to be related to the ability of the pyran derivative to form a discotic mesophase structure. This phenomenon is believed to be general.