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The theoretical spectra of electroluminescent polymers are studied with time-dependent density functional theories, followed by a systematic scheme with a symmetry restriction to extrapolate the absorption and emission corresponding to infinite chains avoiding periodic boundary conditions. Application to poly(p-phenylene vinylene) (PPV) and the derivatives has been attempted, and the hybrid B3LYP is concluded to be the most suitable functional for computation. The theoretical excitation energies of PPV by B3LYP/6-31G*//B3LYP/STO-3G and B3LYP/6-311G* are 2.107 and 2.027 eV, respectively. With optimization performed by single-excited configuration interaction, the emission spectroscopy can be estimated. By our scheme, the Stokes shift of PPV is calculated to be 0.223 eV, which corresponds to approximately 62 nm in the spectral region.