Bright green-to-yellow emitting Cu(I) complexes based on bis(2-pyridyl)phosphine oxides: synthesis, structure and effective thermally activated-delayed fluorescence

A family of brightly luminescent dinuclear complexes of [Cu(mu(2)-X)((NN)-N-boolean AND)](2) type (X = I or SCN) has been synthesized in 76-90% yields by the reaction of bis(2-pyridyl)phosphine oxides ((NN)-N-boolean AND) with the corresponding Cu(I) salts. The X-ray diffraction study reveals that the Cu2I2 core of the [Cu(mu(2)-I)((NN)-N-boolean AND)](2) complexes has either a butterfly-or rhomboid-shaped structure, while the eighth-membered [Cu((SCN)(NCS))Cu] ring in the [Cu-2(SCN)(2)((NN)-N-boolean AND)](2) complexes is nearly planar. In the solid state, these compounds exhibit a strong green-to-yellow emission (lambda(em)(max) = 536-592 nm) with high PLQYs (up to 63%) and short lifetimes (1.9-10.0 mu s). The combined photophysical and DFT study indicates that the ambient-temperature emission of the complexes obtained can be assigned to the thermally activated-delayed fluorescence (TADF) from the (1)(M + X)LCT excited state, while at 77 K, phosphorescence from the (3)(M + X) LCT state is likely observed.