Analytical Sciences

Abstract − Analytical Sciences, 21(3), 303 (2005).

Molecular Probe for a Fluorous Medium: Long-Lived Phosphorescence of α-Diketones in Perfluoromethylcyclohexane at Room Temperature
Yasuyuki TSUBOI,*,** Kensaku OKADA,* Shoji ISHIZAKA,* and Noboru KITAMURA*
*Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
**SORST (Solution Oriented Research for Science and Technology), JST (Japan Science and Technology Corporation), Japan
We found that α-diketones (2,3-butanedione (BD) and 1-phenyl-1,2-propanedione (PPD)) were very suitable luminescence probes for studying the properties of a perfluorinated solvent (i.e., fluorous solvent; perfluoromethylcyclohexane (PFMC)), since these compounds were soluble in PFMC and showed long-lived phosphorescence even at room temperature. The phosphorescence lifetime (τp) of BD in PFMC (650 µs) was much longer than that in cyclohexane (CH, 270 µs). The longer τp value of BD in PFMC was ascribed to the variation of the intersystem crossing rate constant (kisc) from the excited triplet state (T1) to the ground state (S0) with the solvent. Some possible reasons for the change in kisc were discussed in terms of solute-solvent interactions. Furthermore, by utilizing phosphorescence quenching of BD by pyrene, we determined a rate constant of the diffusion-controlled reaction in PFMC. Characteristic behaviors of mixing/separation processes between PFMC and a common organic solvent observed by Schlieren photographs were also reported.