The photoelectron signal of the singly deprotonated fluorescein anion is found to be highly dependent on the relative polarization between pump and probe pulses, and time-resolved photodetachment anisotropy (TR-PA) is developed as a probe of the rotational dynamics of the chromophore. The total photoelectron signal shows both rotational and vibrational wavepacket dynamics, and we demonstrate how TR-PA can readily disentangle these dynamical processes. TR-PA in fluorescein presents specific opportunities for its development as a probe for rotational dynamics in large biomolecules as fluorescein derivatives are commonly incorporated in complex biomolecules and have been used extensively in time-resolved fluorescence anisotropy measurements, to which TR-PA is a gas-phase analogue. T he measurement and control over molecular alignment has been an important tool in both solution and gas-phase chemical physics and biophysics, as it provides a route to monitoring structural change and controlling molecular dynamics. For example, time-resolved fluorescence anisotropy (TR-FA) and imaging have enabled the direct probing of biophysical processes, 1−3 while alignment experiments in the gas phase have opened up countless avenues for probing molecular-frame processes. 4−6 Some of the experimental tools are transferable between solution and gas phases, and fluorescence measurements have elegantly demonstrated their potential power in large isolated molecular systems, 7−14