Which fluorophore is noted for having a structure that leads to much brighter fluorescence?

Phycoerythrin is known for its unique structure, which contributes to its remarkably bright fluorescence. It is a phycobiliprotein predominantly found in red algae and cyanobacteria. The structure of phycoerythrin includes numerous chromophores that absorb light efficiently and then re-emit it at a longer wavelength. This multi-chromophoric arrangement enhances its fluorescent intensity, making it much brighter than many other fluorophores when excited.

In flow cytometry and various fluorescent applications, the high quantum yield of phycoerythrin translates to a strong signal, making it particularly useful in assays that require high-sensitivity detection. Its ability to be excited by multiple wavelengths and to emit brightly in the green range makes it a preferred choice for labeling antibodies and other biomolecules, especially in applications that involve multiparametric analysis.

The other options, while they may show fluorescence, do not achieve the same level of brightness or are less suitable for applications that require intense and clear signals. For instance, fluorescein is bright but does not match the intensity of phycoerythrin under similar conditions. Chlorophyll, while it has fluorescent properties, is primarily involved in photosynthesis and not used for the same types of fluorescent applications.