One of the major challenges in biology is to understand better the molecular regulation of signaling pathways that control complex cellular processes such as motility and proliferation. The experimental approaches employed in such investigations must gather information on changes in protein structure and function over a hierarchy of biological organization, spanning the nanometer dimensions of single protein complexes to micron-sized lamellipodia. These structural and organizational changes take place over correlated timescales that span milliseconds or less for the formation of protein complexes, to minutes for movements of an entire cell. Caged effector molecules and site-selective introduction of photochromic probes within biomolecules have been used as part of an approach for optical control of biomolecular interactions and activities within cells. The photochromic spiropyran-containing molecules undergo rapid and reversible, optically driven transitions between a colorless spiro state and a brightly colored merocyanine state.