The present study offers direct evidence for homoconjugation by employing optical and vibrational spectroscopy to investigate the interplay between the microstructure and solid-state optical properties of PPM and its derivative poly(2,4,6-trimethylphenylene methylene). In particular, polarized Raman and PL spectroscopy of melt-drawn fibers reveal a preferentially perpendicular orientation of the phenylene rings relative to the fiber axis and, simultaneously, a preferentially parallel orientation of the transition dipole moment. PL spectroscopy under applied hydrostatic pressure yields a nearly fourfold increase in PL intensity at 8 GPa, together with a surprising absence of excimer emission. These characteristics, being highly atypical of conventional π-conjugated polymers, highlight the different origin of the optical properties of PPMs and unique opportunities for applications.