CHARGE-CONJUGATION SYMMETRY-BREAKING IN POLY(PHENYLENEVINYLENE) DERIVATIVES

When the phenylene monomer of poly(phenylenevinylene) (PPV) is substit uted to form one of the well-known PPV derivatives, the charge-conjuga tion symmetry (CCS) of the unsubstituted polymer is broken, giving ris e to a new optical absorption band. A model Pariser-Parr-Pople-like Ha miltonian neglecting the side groups would fail to allow for the break ing of this symmetry and would miss the general property that the CCS- even excitations of the unsubstituted polymer acquire a transition dip ole moment whenever CCS is broken.