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.