rotational correlation time \(\tau_{\text{c}}\), \(\theta\)

https://doi.org/10.1351/goldbook.RT07474
Parameter describing the time dependence of the tumbling of a molecular entity in a medium of viscosity \(\eta\). 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, \(D_{\text{r}}\), in turn related to the hydrodynamic molecular volume of the fluorophore, \(V\), and to \(\eta\) (see Note 3).
Notes:
  1. Mathematical definition: \(r(t) = r_{\text{0}}\, exp\! \left ( -\frac{t}{\tau_{\text{c}}} \right )\) with \(r(t)\) the @ET07370@ at time \(t\) and \(r_{\text{0}}\) the fundamental @ET07370@.
  2. In the case of a spherical emitting species reorienting itself in a homogeneous fluid, \(\tau_{\text{c}} = \frac{1}{6D_{\text{r}}}\).
  3. 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@.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 416 [Terms] [Paper]