The electronic and molecular structures of a two-dimensional septet-state molecule (S=3), 1,3,5-tris(p-methoxyphenylmethylene)benzene A, were investigated by single-crystal ESR spectroscopy. A was designed for a prototype core model for discotic liquid crystalline organic high-spin molecules. Tris(cr-benzoyl)benzene was adopted as the host crystal and its crystallographic parameters were determined by X-ray diffraction : the space group Pi with Z=4, a=11.99 A, b=21.94 A, c=7.82 A, alpha=98.0 degrees, beta=90.9 degrees, and gamma=94.1 degrees. The effect of the methoxy functional group on the fine-structure constants was found : the effect showed up in the significant reduction of the fine-structure constant D value, showing the modification of the topologically controlled robust pi spin polarization. The observed finite E value is in accord with the molecular symmetry and crystal structure of the host molecule.