Low-lying band shapes of absorption and fluorescence spectra for a member of a newly synthesized family Of phenylene-containing oligoacenes (POA 6) reported in J. Am, Chem. Soc. 2012, 134, 15351 are studied theoretically with two different approaches with TIPS-anthracene as a comparison. Underlying photophysics and exciton-phonon interactions in both molecules are investigated in details with the aid, of the time-dependent density functional theory and multimode Brownian oscillator model. The first two low-lying excited-States of POA 6 were found to exhibit excitation. characteristics spanning entire conjugated backbone despite the presence of antiaromatic phenylene section. Absorption and fluorescence spectra calculated from both time-dependent density functional theory and multimode Brownian oscillator model are shown to reach god agreement with experimental ones: The coupling between phonon modes and optical transitions is generally weak as suggested by the multimode Brownian oscillator model. Broader peaks of POA 6 Spectra are found to relate-to Stronger coupling between low frequency phonon modes such as backbone twisting (with frequency <300 cm(-1)) and optical transitions. Furthermore, POA 6 exhibits weaker exciton-phonon coupling for the phonon modes above 1000-cm(-1) compared to TIPS-anthracene owing to extended conjugated backbone. A significant coupling between an in-plane breathing mode localized around the antiaromatic phenylene segment With frequency at 1687 cm(-1) and optical transitions for the firs two excited-states of POA 6 is also observed.