Fluorescence lifetimes of 33 alkanes were measured at 25°C using a 0.7 ns pulse radiolysis system and the relationship between molecular structure, fluorescence lifetime (τ), quantum yield (Φf) and radiative rate constant (R = Φf τ) is discussed. The τ's showed a large dependence on the molecular structure, however, the R-values were approximately constant for groups of alkanes: R = 1.3×106 s-1 for n-alkanes, R ≈ 4×106 s-1 for aliphatic vicinally substituted dimethyl alkanes, R = 7×106 s-1 for cyclohexane and alkylcyclohexanes, and R = 10×106 s-1 for di- and trimethylcyclohexanes. The excited state lifetimes of some non-fluorescing alkanes were also determined from steady-state photolytic quenching data and found to be very low (≤ 0.3 ns).
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics