Tetra(4-(diethylamino)phenyl)ethene (TPE-4N), a new derivative of tetraphenylethene (TPE), is facilely prepared in one step from bis(4-(diethylamino)phenyl)methanone in a good yield of 85%. TPE-4N shows aggregation-induced emission (AIE) with high solid-state fluorescence quantum yields up to 63.5%. It has strong proton capture capability, allowing for reversible fluorescence switching in acidic and