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 @ET07370@ does not decay to zero but to a steady value, \(r_{\mathrm{\infty }}\), called residual @ET07370@. In the case of a single rotational correlation time, \(\tau _{\mathrm{c}}\) or \(\theta \), the decay of @ET07370@ following δ-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 @ET07370@.