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(α-benzoyl)benzene was adopted as the host crystal and its crystallographic parameters were determined by X-ray diffraction: the space group Pi withZ=4,a=11.99 A,b=21.94 A,c=7.82 A, α=98.0°, β=90.9°, and γ=94.1°. 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 π spin polarization. The observed finite E value is in accord with the molecular symmetry and crystal structure of the host molecule.