Methods of performing assays with long lifetime compounds are disclosed. The long lifetime compounds have a lifetime of 4 ns or longer and relate to the structure:
Linked reactive groups or conjugated substances may generally be located at R
a
, R
b
, or R
c
. Adjacent substituents R
a
and R
b
may form a substituted, 5- or 6-membered heterocyclic group with one ring nitrogen. R
e
and R
f
may both be H, R
e
may be a sulfo group, or adjacent substituents R
e
and R
f
may form a cyclic ring structure. The long lifetime compounds contain at least one sulfo group and at least one ionic group, reactive group, or conjugated substance.