Designing luminescent diimine-Cu(I)-phosphine complexes by tuning N-ligand and counteranions: correlation of weak interactions, luminescence and THz absorption spectra

Herein, six new [Cu(N<^>N)(P<^>P)](+/0) complexes with different N-ligands and counteranions, [Cu-2(dmp)(2)(bdppmapy)I-2] (1), [Cu-2(dmp)(2)(bdppmapy)(CN)(2)]center dot 3CH(3)OH (2), [Cu(dmp)(bdppmapy)](BF4) (3), [Cu(dmp)(bdppmapy)](ClO4) (4), [Cu(phen)(bdppmapy)](BF4) (5), and [Cu(phen)(bdppmapy)](ClO4) (6), have been synthesized and characterized (bdppmapy = N,N-bis[(diphenylphosphino)methyl]-2-pyridinamine, phen = 1,10-phenanthroline, dmp = 2,9-dimethyl-1,10-phenanthroline). Single-crystal X-ray diffraction showed that different counteranions help to construct various stacking modes 1D-3D via weak interactions, such as pi-pi, C-H center dot center dot center dot pi and C-H center dot center dot center dot X (X = F, O). Photophysical analysis showed they have yellow-green to yellow-orange emission within a range of 504-569 nm, and excellent photophysical properties with quantum yields from 2.6% (2) to 77% (4). In this study, these results indicate that the pi-pi stacking and C-H center dot center dot center dot X (X = O, F) weak interactions help to enhance the rigidity of these structures and further improve their luminescence quantum yields. In addition, we have explored the nature of the complexes emission mechanism through theoretical calculations. According to DFT/TD-DFT calculations, the luminescence behavior of the six complexes is ascribed to MLCT or (M + X)LCT. THz spectra were applied to explore the relationship between weak interactions and luminescence. These results have opened up a new direction in the characterization of the properties of luminescent materials.