A new series of neutral protomesogenic EuIII tris(β‐diketonate) adducts with different Lewis bases have been synthesized. Only one of the complexes is liquid‐crystalline and displays smectic A and nematic mesomorphism over a broad temperature range. Quantum‐chemistry and small‐angle X‐ray scattering methods have permitted the evaluation of the influence of the structure of the Lewis base on the anisometry of EuIII adduct molecules and their subsequent supramolecular organization. The structural features of the presented compounds allow the creation of vitrified optically isotropic and self‐organized films with effective red luminescence. The luminescence spectra of aligned thin films of a liquid‐crystalline EuIII complex are also described.