New chromophoric molecules of 1,1-di(thiophen-2-yl)-2,3,4,5-tetraphenyl-silole (T2TPS), 9-(diphenylmethylene)-9H-fluorene (DPMF), and tetraphenyletheneare (TPE) are designed and synthesized. When molecularly dissolved in common organic solvents, the molecules are practically nonemissive. Addition of poor solvents induces the molecules to aggregate, which turns the emission "on" and boosts their luminescence efficiencies dramatically ("aggregation-induced emission" or AIE). The photoluminescence (PL) of T2TPS and TPE layers adsorbed on the TLC plates can be turned "off" and "on" continuously and reversibly by solvent exposure and evaporation. Transformation from amorphous phase to crystalline structure blue-shifts the PL spectrum of T2TPS and enhances its intensity. A light-emitting devices (LEDs) device based on TPE is fabricated, which emits a blue light of 447 nm with a low turn-on voltage of 2.9 V.