To investigate whether the substituent itself joins the molecular photo-physical processes, we first calculate the electronic absorption and emission spectra of DPND6 and DPND monomers with the inclusion of vibration motions. The calculated results are shown in Fig. , in which we have included the outer reorganization energies of 0.038 eV and 0.045 eV for DPND6 and DPND to fit the observed Stokes shifts. It is seen that both monomers have very similar spectral shapes, and the vibrationally-resolved peaks are mainly from the stretching vibration of crossconjugated skeletons with frequencies of 1356 cm -1 and 1360 cm -1 for DPND6 and DPND monomers, respectively. These data manifest that the alkyl side chain has a slight perturbation to electronic excited states, and the molecular excited-state properties as well as photo-physical processes should be dominantly determined by the cross-conjugate skeletons. Therefore, in the later calculations the hexyl side chain is replaced by the ethyl side chain to save computation costs.