ELECTRON-HOLE SYMMETRIES IN CONDUCTING POLYMERS

New experimental results from both infrared (IR) absorption of n-type and p-type doped poly(paraphenylene-vinylene) (PPV) and photoinduced IR absorption in undoped PPV are reported. We find the effective Coulomb correlation energy associated with the negatively charged bipolarons is approximately 0.4 eV greater than for positively charged ones. This difference implies that the electron-hole symmetry may be intrinsically broken within non-degenerate ground state conjugated polymer hosts and, if so, goes against the common notion of symmetry as stated in currently existing theoretical models.