Carbazolyl-substituted phosphoramides as ligands for Mn(II) luminescent complexes

Ligands containing the {O=P} donor moiety are of paramount importance in the sensitization of Mn(ll) luminescence [1]. Besides mono- and polydentate phosphine oxides, ligands based on the phosphoramide skeleton revealed to be suitable for the preparation of luminescent Mn(II) complexes [2,3], and it was observed an improvement of the luminescence on increasing the light­ harvesting features of the substituents on the ligands. A potential fragment able to efficiently absorb UV radiation is the carbazolyl moiety. The phosphoramide N,N,N',N'-tetramethyl-P-carbazol-9-ylphosphonic diamide (L) was successfully coordinated to MnX2 halides (X = Cl, Br, I), obtaining tetrahedral complexes having generai formula [MnX2L2]. The structures were ascertained by means of single-crystal X-ray diffraction. The three complexes showed noticeable luminescence in the green region upon excitation with UV radiation, attributed to the Mn(II) 4T1(4G) GA1(6S) transition. The luminescence lifetimes are strongly dependent upon the choice of the coordinated halide.