Luminescence properties and their photoinduced control of the electric dipole transitions of a Eu(III) complex that has photochromic triangle terarylenes ligands, tris(hexafluoroacetylacetonato)bis[4,5-bis(5-methyl-2-phenylthiazol-4-yl)-2-phenylthiazole]europium(III) (Eu(hfa)(3)(THIA)(2)), were studied. Fairly high photochromic reactivity of the ligand between the open-ring and closed-ring forms were found to be maintained even in the complex, and reversible color change could be observed many times. The photocyclization and the cycloreversion quantum yields of the Eu(hfa)(3)(THIA)(2) were found to be 37% and 3.4%, respectively. The thermal stability of the closed-ring form of THIA ligand is significantly improved in the Eu(III) complex. The D-5(0)-F-7(2) transition intensity of the Eu(III) complex with open-ring form ligands (Eu(hfa)(3)(THIA)2-O) is larger than that of the Eu(III) complex with closed-ring form ligands (Eu(hfa)(3)(THIA)2-C). The radiative rate constants of Eu(hfa)(3)(THIA)2-O and Eu(hfa)(3)(THIA)2-C are estimated to be 1.7 x 10(2) and 1.5 x 10(2) s(-1), respectively. The reversible control of the emission properties of the Eu(III) complex by the photochromic reactions is demonstrated for the first time.