Torsional rearrangements of aryl-substituted anthracenes measured by phase fluorometry.
We examined the fluorescence phase angle spectra of aryl-substituted anthracenes in viscous solvents. These phase angles reflect the wavelength-dependent lifetimes displayed by the fluorophores. At intermediate viscosities the phase angles increased and decreased in accordance with the valleys and peaks of the structured emission spectra. At lower and higher temperatures the phase angles were independent of emission wavelength, which is equivalent to decay times which are independent of emission wavelength. We attribute the wavelength-dependent phase angles to rotation of the unsaturaled side chains towards a conformation more coplanar with the anthracene ring. By comparative studies with 9,10-di(alpha-naphthylanthracene), 9,10-di-phenylanthracene, and 9-vinylanthracene we showed that lower temperatures are required to inhibit rotation of the smaller phenyl and vinyl substitutents. Since these excited-state rearrangements are sensitive to the motional freedom allowed by the surrounding solvent, we suggest that this phenomenon may serve as a probe of volume fluctuations in macromolecules.
Laczko
G
G
University of Maryland, School of Medicine, Department of Biological Chemistry, Baltimore, MD 21201, USA.
Lakowicz
J R
JR