Photochromic core structure of BTEs was configured in the design ofBT(2,3-Bis(2,5-dimethylthiophen)-5-phenylethynylthiophene) andNT(2,3-Bis(2,5-dimethylthiophen)-5-(4-methoxyphenyl)-1,3-butadiene-1,1,4,4-tetracarbonitrile).BTexhibits regular photochromic behavior in hexane when excited with UV (254 nm) and visible light (>400 nm). The solution can be cycled between pink colors and colorless. Correspondingly,NT, with a more electron-withdrawing group attached, the photochromic reactivity was totally quenched. It is the lowered electron density on reactive carbon atoms in LUMO that influence the photochromism, which is one of the key elements to photochromism. Apart from the distance between reactive atoms, electron distribution on reactive atoms is another important key to the configuration of photochromic dyes.