Electronic properties of alkoxy derivatives of poly(para-phenylenevinylene) , investigated by time-dependent density functional theory calculations

Geometries and energy gaps of poly(para-phenylenevinylene) oligomers (OPV_N) and their alkoxy derivatives were investigated, based on quantum-chemical calculations. This oligomer series includes poly(para-methoxy-PV) (DMO-OPV_N), poly(para-hexoxy-PV) (DHO-OPV _N) and poly(2-methoxy,5-(2′-ethyl-hexyloxy)-PV) (MEH-OPV _N). Potential energy hypersurfaces of all OPV₂ and OPV₂-alkoxy derivatives were calculated by the semiempirical AM1 and ab initio method at the HF/3-21G and HF/6-31G levels. The results obtained indicate that OPV₂ provide two conformational structures, one coplanar and one twisted. For its alkoxy derivatives, the stable conformation was found to be that in which the two adjacent phenylene rings were coplanar. An intramolecular weak hydrogen bond interaction was also found to occur between the oxygen atom of the alkoxy derivatives and the hydrogen atom of the vinylene linkage. By using these linear relationships, they can be employed to semiquantitatively estimate the first excitation energy. We introduce the relationships with the working function of E_expt = 0.604E _{TDDFT-B3LYP/6-31G} + 0.947 and E_expt = 0.604E _{TDDFT-B3LYP/6-31G*} + 0.983, based on the geometry obtained from HF/3-21G for corrected the extrapolated energy gaps of DMO-OPV_N, DHO-OPV_N and MEH-OPV_N. It was found that satisfactory linear relationship and TDDFT method can be used to predict the lowest excitation energies for compounds in these systems and applicable to the design of new conducting polymers.