发光聚合物中光激发引起磁化率改变的新现象

Photoinduced Variation of Magnetic Susceptibility in Luminescent Polymers

揭示了发光聚合物中光激发引起的一个新现象:光激发即吸收一个光子使发光聚合物中的正双极化子分裂成两个带正电的极化子,从而使发光聚合物中的磁化率改变。

It is discovered by molecular dynamics that a positivebipolaron in luminescent polymers is split into two polarons by absorbing a photon. Because the energy to create a bipolaron is less than the energy to create two polarons, the main carriers in luminescent polymers are bipolarons. For a positivebipolaron, both εhigh and εlow levels in the gap are empty, and the valence band is fully occupied. After absorbing a photon, an electron is excited from the valence band to εlow level in the gap. It induces the change of the original atomic configurations and electronic states. Our computer simulations reveal that a positivebipolaron in luminescent polymers will be split into two polarons after an electron is excited from the valence band to εlow level in the gap. The reason of the split is as follows. A bipolaron or a polaron in luminescent polymers is a composite particle, which has intrinsic structures including atomic configurations and electronic states. Due to the instability of lowdimension, the intrinsic structures of a bipolaron will be changed by absorbing a photon. In a polaron, either of εhigh and εlow levels in the gap is occupied by only one electron, and other states are either occupied by two electrons with opposite spins or empty. Therefore, the spin of a polaron is 1/2. Whereas in a bipolaron, all electronic states, including εhigh and εlow levels in the gap, are either occupied by two electrons with opposite spins or empty. So the spin of a bipolaron is zero. Since a polaron possesses spin magnetic while a bipolaron does not, the Pauli susceptibility will be changed when a positivebipolaron is split into two polarons due to absorbing a photon. So this phenomenon is photoinduced variation of magnetic susceptibility. It is a new phenomenon in luminescent polymers, and would be of interest both in basic sciences and in technology.