The electronic structures and the structural deformations of silicon containing poly(p-phenylenevinylene) (PPV) polymers have been studied theoretically. The results of the calculations indicate that the regular π conjugated system is effectively interrupted by the organosilicon units yielding a blue emission. It has also been observed that substitution of methoxy on vinylene group caused significant structural deformation of the PPV lumophore, and subsequently, decreased the ionization potential (IP) and increased the electron affinity of the SiBu PPV. Experimentally, it is known that light emitting diodes made of silicon containing copolymers operate at low voltages, due to the reduction of the LUMO level in the luminescence polymers. The flat deformation of the PPV moiety induced a red shift of the absorption maxima. The substitution of phenyl ring on silicon atoms constrained free rotation around the Si- C bond increasing the torsional angles of the lumophore and caused slight blue shift of absorption peak. Substitution of the cyano group on the vinylene moiety increased the ionization potential as well as the electron affinity. On the other hand, the electron donating methoxy group decreased the ionization potential and electron affinity. Those calculated results agree well with the experimental observations. The density functional calculation method, which account for electron correlation, yielded much more accurate values for the HOMO-LUMO gap than the Hartree-Fock method.
Bibliographical noteFunding Information:
This work was financially supported from the Korea Research Foundation (KRF-2001-005-D00014). We also thank Prof. Suck-Hyun Lee from Ajou University, a member of HOMRC at Seoul National University for helpful discussions.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry