Researchers have developed a sensor based on porous crystalline fibers of a fluorescent dendrimer. The high porosity of the fibers increased their adsorption capacity, making their emission behavior highly sensitive to the presence of solvent vapor. Films of the dendrimer fibers displayed different emission colors depending on the polarity of the solvent vapors they were exposed to. Naked-eye sensors based on porous crystalline dendrimers are attractive for environmental sensing applications.