rotational correlation time, τc, θ

https://doi.org/10.1351/goldbook.RT07474
Parameter describing the time dependence of the tumbling of a molecular entity in a medium of viscosity η. The rotational correlation time can be obtained from the decay of the fluorescence or phosphorescence anisotropy and is related to the average molecular rotational diffusion coefficient, Dr, in turn related to the hydrodynamic molecular volume of the fluorophore, V, and to η (see Note 3).
Notes:
  1. Mathematical definition: r(t)=r0exp(−tτc) with r(t) the emission anisotropy at time t and r0 the fundamental emission anisotropy.
  2. In the case of a spherical emitting species reorienting itself in a homogeneous fluid, τc=16Dr.
  3. Often, the Stokes–Einstein relationship is used for the calculation of Dr, i.e., Dr=RT/6Vη with R the gas constant, T the absolute temperature and V the hydrodynamic molecular volume. However, the use of this relationship at a molecular level is questionable, and Dr should be independently determined by time-resolved fluorescence polarization methods. Compare with rotational relaxation time.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 416 [Terms] [Paper]
Citation: 'rotational correlation time' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.RT07474 RIS BibTex EndNote
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Last revised: February 24, 2014