Re: why do some optical brighteners form suspension?

Most commercial optical brighteners today are triazole-stilbenes or stilbene-
biphenyls; they can form suspesions (as opposed to solutions) in water 
because they are similar to surfactants in that they're partly hydrophobic. If 
you compound them in a way that emphasizes their hydrophobic nature, you 
can easily make them form a suspension.
Optical brighteners do contain chromophores in the sense that they absorb 
certain wavelengths of light; but unlike "simple" chromophores that do only 
that, optical brighteners can re-emit the light absorbed at one frequency at a 
different frequency, usually turning UV radiation (invisible to unaided humans)
into visible radiation, instead of simply reflecting it.