New greenfluorescentprotein (GFP) chromophoreanalogues, namely 4-(diarylmethylene)imidazolinones (DAINs), were readily synthesized under weakly acidic conditions using a novel condensation reaction between methyl imidate (or thioimidate) and ethyl N-(diarylmethylene)glycinate. DAINs showed notable fluorescence properties. Although they were nearly non-fluorescent in the solution, visible emissions