Primuline is a vital fluorescent dye and is used for that reason. It is rarely used for any other purpose.
According to the Color Index, primuline is composed predominantly of the dye with the formula to the left, along with some of the dye illustrated to the right.
R. D. Lillie.
Conn's Biological Stains
Williams & Wilkins, Baltimore, MD., U.S.A.
Aldrich chemical catalogue, 1992
Aldrich Chemical Company, Milwaukee, WI, USA.