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: **

*Source: *

PAC, 2007,*79*, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 416 (https://doi.org/10.1351/pac200779030293)

- Mathematical definition: \(r(t) = r_{\text{0}}\, \text{exp}\! \left ( -\frac{t}{\tau_{\text{c}}} \right )\) with \(r(t)\) the @ET07370@ at time \(t\) and \(r_{\text{0}}\) the fundamental @ET07370@.
- In the case of a spherical emitting species reorienting itself in a homogeneous fluid, \(\tau_{\text{c}} = \frac{1}{6D_{\text{r}}}\).
- Often, the @S06027@–@E01914@ relationship is used for the calculation of \(D_{\text{r}}\), i.e., \(D_{\text{r}} = R\, T/6\, V\eta\) with \(R\) the @G02579@, \(T\) the absolute temperature and \(V\) the hydrodynamic molecular volume. However, the use of this relationship at a molecular level is questionable, and \(D_{\text{r}}\) should be independently determined by time-resolved @F02453@ @P04712@ methods. Compare with @RT07475@.

PAC, 2007,