Magnetic and Luminescent Dual Responses of Photochromic Hexaazamacrocyclic Lanthanide Complexes.

Herein, hexaazamacrocyclic ligand L N6 was employed to construct a series of photochromic rare-earth complexes, [Ln(L N6 )(NO 3 ) 2 ](BPh 4 ) [ 1-Ln , Ln = Dy, Tb, Eu, Gd, Y; L N6 = (3 E ,5 E ,10 E ,12 E )-3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane-3,5,10,12-tetraene]. The behavior of photogenerated radicals of hexaazamacrocyclic ligands was revealed for the first time. Upon 365 nm light irradiation, complexes 1-Ln exhibit photochromic behavior induced by photogenerated radicals according to EPR and UV-vis analyses. Static and dynamic magnetic studies of 1-Dy and irradiated product 1-Dy * indicate weak ferromagnetic interactions among Dy III ions and photogenerated L N6 radicals, as well as slow magnetization relaxation behavior under a 2 kOe applied field. Further fitting analyses show that the magnetization relaxation in 1-Dy * is markedly different from 1-Dy . Time-dependent fluorescence measurements reveal the characteristic luminescence quenching dynamics of lanthanide in the photochromic process. Especially for irradiated product 1-Eu *, the luminescence is almost completely quenched within 5 min with a quenching efficiency of 98.4%. The results reported here provide a prospect for the design of radical-induced photochromic lanthanide single-molecule magnets and will promote the further development of multiresponsive photomagnetic materials.