07473 IUPAC Gold Book - residual emission anisotropy 10.1351/goldbook.RT07473 RT07473 current quantity 1 Photoselected molecules hindered in their rotation (e.g., in lipid bilayers or liquid crystals) do not become randomly oriented even after long time periods. Thus, the emission anisotropy does not decay to zero but to a steady value, \(r_{\mathrm{\infty }}\), called residual emission anisotropy. In the case of a single rotational correlation time, \(\tau _{\mathrm{c}}\) or \(\theta \), the decay of emission anisotropy following $\ce{\updelta\!\mbox{-}pulse}$ excitation is given by: \[r\left(t\right)=(r_{0}- r_{\mathrm{\infty }})\ \exp (- \frac{t}{\tau _{\mathrm{c}}})+r_{\mathrm{\infty }}\] where \(r_{0}\) is the fundamental emission anisotropy. The term residual anisotropy is to be preferred to 'limiting anisotropy'. anisotropy https://goldbook.iupac.org//terms/view/AT06776 emission anisotropy https://goldbook.iupac.org//terms/view/ET07370 PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 414 (https://doi.org/10.1351/pac200779030293) https://goldbook.iupac.org/terms/view/RT07473/html https://goldbook.iupac.org/terms/view/RT07473/json https://goldbook.iupac.org/terms/view/RT07473/plain Citation: 'residual emission anisotropy' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.RT07473 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-04-28T23:19:42+00:00