Magnetic and Luminescent Dual Responses of Photochromic Hexaazamacrocyclic Lanthanide Complexes

Abstract

Herein, hexaazamacrocyclic ligand L^N6 was employed to construct a series of photochromic rare-earth complexes, [Ln(L^N6)(NO₃)₂](BPh₄) [<b>1-Ln</b>, Ln = Dy, Tb, Eu, Gd, Y; L^N6 = (3<i>E</i>,5<i>E</i>,10<i>E</i>,12<i>E</i>)-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 <b>1-Ln</b> exhibit photochromic behavior induced by photogenerated radicals according to EPR and UV-vis analyses. Static and dynamic magnetic studies of <b>1-Dy</b> and irradiated product <b>1-Dy</b>* 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 <b>1-Dy</b>* is markedly different from <b>1-Dy</b>. Time-dependent fluorescence measurements reveal the characteristic luminescence quenching dynamics of lanthanide in the photochromic process. Especially for irradiated product <b>1-Eu</b>*, 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.