Cyclodextrin-enhanced room-temperature phosphorescence (CD-RTP) is an analytical technique that offers well-resolved spectra and subpicogram detection limits. When polynuclear aromatic hydrocarbons (PAHs) are included in cyclodextrin molecules in the presence of a heavy-atom moiety such as 1,2-dibromoethane, they exhibit intense, well-defined phosphorescence emissions, often with distinct vibrational structure. Moreover, the cyclodextrin moiety inhibits quenching of PAH phosphorescence by O2 present in the bulk solution.
Cyclodextrins (CDs) are made up of glucose monomers coupled to form a rigid, conical structure with an interior hydrophobic cavity. The most common CDs, denoted by α, β, and γ, are composed, respectively, of six, seven, and eight monomers. Initially, each CD contains one or more water molecules, produced during the monomer coupling. Because these included water molecules are easily displaced by hydrophobic species that will fit into the CD interior, cyclodextrins have a unique ability to form stable inclusion complexes with a variety of molecules.
This inclusion capability has led to an important use of cyclodextrins in luminescence spectroscopy. Cyclodextrins have been found to enhance fluorescent and phosphorescent emissions from molecules present in the CD cavity.1,2,3,4,5 Of particular interest is the phenomenon of cyclodextrin-enhanced room-temperature phosphorescence (CD-RTP), which suggests a highly-selective analytical technique based on the molecular geometry of the lumiphor.
Chromophores such as polynuclear aromatic hyrdocarbons (PAHs) exhibit virtually no phosphorescence in conventional fluid media. Scypinski and Cline Love report, however, that intense room-temperature phosphorescence occurs when these well-known carcinogens are present, with an external heavy