Electronic structure and optical properties of mixed phenylene vinylene/phenylene ethynylene conjugated oligomers

We present a combined experimental and theoretical investigation of the photophysical properties of four pi-conjugated oligomers with varying chemical constitutions. Three of these contain alkoxy-substituted p-phenylene vinylene/ethynylene units with a phenylene, anthracene, or p-dialkoxyphenylene moiety as the central aromatic ring; the fourth oligomer contains only p-dialkoxyphenylene vinylene units. The electronic structure and optical properties are investigated by combining UV-vis, fluorescence, and electrochemical techniques with quantum-chemical semiempirical calculations. The simulated absorption spectra are in excellent agreement with the experimental data and illustrate the role of the central aromatic ring on the nature of the lowest excited state.