The present invention relates to materials and methods useful in the study of cells and species associated with cells. Materials of the present invention may include emissive, photostable organic molecules (e.g., conjugated polymers, conjugated oligomers) that are appropriately functionalized to interact with a cell with essentially no disruption in normal cell functioning. The present invention may be useful in, for example, cell imaging, cell tracking, in vivo monitoring of cellular events, drug delivery, and determination of biological species. In one embodiment, a conjugated polymer or oligomer may be internalized into a cell and may exhibit a strong and stable emissive signal, allowing the cell to be monitored under extensive microscopic conditions for extended periods of time.