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: rt = r0.exp(-t/τc) with rt the @ET07370@ at time t and r0 the fundamental @ET07370@.
- In the case of a spherical emitting species reorienting itself in a homogeneous fluid, τc = 1/6Dr.
- Often, the @S06027@–@E01914@ relationship is used for the calculation of Dr, i.e., Dr = RT/6Vη 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 Dr should be independently determined by time-resolved @F02453@ @P04712@ methods. Compare with @RT07475@.

PAC, 2007,