What does rhodamine phalloidin do?

Figure 1. Chemical structure for Phalloidin-Tetramethylrhodamine Conjugate

Rhodamine phalloidin is a popular conjugate used as a fluorescent label for F-actin. The paired molecules work in tandem on fixed cells, since they are too large to be permeable to living cell membranes. The cyclic phalloidin molecule specifically binds and stabilizes the F-actin of the cellular cytoskeleton; the rhodamine acts as a marker, fluorescing in the orange-red spectrum and allowing visualization of the filamentous network within the cell.