Effect of cyclodextrin cavity size on sensitization of room-temperature phosphorescence of biacetyl

The triplet-triplet energy-transfer reactions of several polynuclear aromatic compounds are enhanced to different degrees in alpha -,beta and gamma-cyclodextrin (CD) media when biacetyl is used as the acceptor species. The phosphorescence intensity of biacetyl increases as the size of the CD cavity increases. The CD cavities have specific dimensions which place constraints on the number of donor and acceptor molecules that can be included in them. The larger the cavity, the better it is able to include the reactants and, apparently, position them to increase the rate of triplet-triplet energy transfer. Compounds such as chrysene and triphenylene, which are unresponsive as biacetyl sensitizers in alpha-CD and beta-CD, are excellent sensitizers of biacetyl in the larger gamma-CD. Typically, limits of detection of 1 x 10(-6), 5 x 10(-7) and 1 x 10(-7)M were found with alpha-CD, beta-CD and gamma-CD, respectively.