Solitons in doped β-carotene films: optical absorption and Esr studies

We present opticalabsorption and electron spin resonance studies of iodine and AsF5 doped β-carotene films. We show that stable soliton-like defects are formed upon p-doping. The spin to charge ratio found experimentally is ∼-0.02, indicating that nearly all defects are spinless. The absorption spectrum is characterized by a single intragap band and set of infrared active vibration lines; evidence that there is significant structural relaxation upon charge transfer. A possible spinless species is the dication in which two soliton defects are formed. The small number of spins observed are probably due to β-carotene radical cations.