Tetraphenylethylenes derivatives 1,2-bis(4-bromophenyl)-1,2-diphenyl-E-ethene (1) and 1,2-bis(4-methoxyphenyl)-1,2-diphenyl-E-ethene (2) are synthesized. When the molecules are molecularly dissolved in acetonitrile, they are practically nonemissive ("off"). When a non-solvent of water is added, they aggregate and emit intensely ("on"). The quantum efficiency increases with an increase in the added amount of water. Even when they are blended with poly(methyl methacrylate), the resultant films still show bright emissions.