chromophores having two - photon or other multi - photon absorptivity . the chromophores are based on a structure of four stilbenoid groups attached to a paracyclophane core , where each stilbenoid group comprises a nitrogen - containing organic group attached by its nitrogen atom to a stilbenoid arm . in particular embodiments , at least one of the stilbenoid groups includes a sulfonium , ammonium , selenium , iodonium or phosphonium moiety . the chromophores have utility as photo - polymerization initiators and two - photon fluorophores for biological imaging .