Green Phosphorescent Zn(II) Halide Complexes with N,N,N′,N′-tetramethyl-P-indol-1-ylphosphonic diamide as Ligand

Tetrahedral Zn(II) complexes having general formula [ZnX2{O=P(NMe2)2Ind}2] (X=Cl, Br, I, NCS) were isolated from the reaction between the indol-1-yl substituted phosphoramide N,N,N′,N′-tetramethyl-P-indol-1-ylphosphonic diamide O=P(NMe2)2Ind and anhydrous Zn(II) precursors under mild conditions. The structures of the three halide derivatives were ascertained by single-crystal X-ray diffraction. The bromo- and iodo-derivatives revealed to be appreciably luminescent in the green region upon excitation with light below 300 nm, with emission bands centred between 520 and 530 nm. The large Stokes shifts and the excited state lifetimes in the milliseconds range indicated that triplet excited states are involved in the emission. TD-DFT calculations indicated that the luminescence is related to a ligand-centred transition with the involvement of triplet states.