We report direct observation of radioisotopically labeled molecular structural changes in these photochemical processes with the interference effect of electron-capture X-ray emitted by nuclear transformations in radioactive atoms. The azobenzene derivative molecules were specifically reacted with the radioactive atoms (In-111) by using ionic bonds between the carboxyl groups in the azobenzene derivatives and the radioactive atoms. The trans-cis isomerization of the monolayer on the substrate was distinctly reflected in the period of the observed interference fringes. We measured the trans-cis photoisomerizations on the same substrate during seven alternations by using UV-visible light irradiation. As a result, we observed irreversible photochromism in the monolayer of azobenzene derivatives on the substrate because of the close packing of chromophores.