A Smart Photochromic Semiconductor: Breaking the Intrinsic Positive Relation Between Conductance and Temperature

Breaking the intrinsic rule of semiconductors that conductivity increases with increase of temperature and realizing a dramatic dropping of conductivity at high temperature may arouse new intriguing applications, such as circuit overload or over-temperature protecting. This goal has now been achieved through T-type electron-transfer photochromism of one organic semiconductor assembled by intermolecular cation...pi interactions. Conductivity of the viologen-based model semiconductor (H(2)bipy)(Hox)(2) (H(2)bipy=4,4 '-bipyridin-1,1 '-dium; ox=oxalate) increased by 2 orders of magnitude after photoinduced electron transfer (a record for photoswitchable organic semiconductors) and generation of radical cation...pi interactions, and fell by approximately 81% at 100 degrees C through reverse electron transfer and degeneration of the radical cation...pi interactions. The model semiconductor has at least two different electron transfer pathways in the decoloration process.