Luminescent cationic/neutral Cu(I) complexes for use in light-emitting diodes: Synthesis, structural characterization, DFT studies and properties

Cationic and neutral mononuclear Cu(I) complexes, [Cu(PPh3)2(PmH)]BF4 (1a), [Cu(DPEphos) (PmH)]BF4 (2a), [Cu(Xantphos) (PmH)]BF4 (3a), [Cu(PPh3)2(Pm)] (1b), [Cu(DPEphos) (Pm)] (2b) and [Cu(Xantphos) (Pm)] (3b) (PPh3 = triphenylphosphine, DPEphos = bis(2-diphenylphosphinophenyl)ether, Xantphos = 9, 9-dimethyl-bis (diphenylphosphino)xanthenes, PmH = 2-(pyridin-2-yl)benzimidazole, Pm=(2-(Pyridin-2-yl)benzimidazolate), have been prepared and characterized by IR, 1H NMR, 13C NMR, 31P NMR, XRD, elemental analysis and X-ray crystal structure analysis. The structural analysis shows that each of Cu(I) complexes includes a tetrahedral [Cu (NN) (PP)]+ moiety, and temperature variation from 99 K to 298 K leads to the change of bonds lengths, angles and weak interactions. Meanwhile, theoretical calculations indicate that the differences between cationic and neutral Cu(I) complexes affect the composition of HOMO and LUMO orbitals, and the effect of temperature on Mulliken atomic charges is limited. Furthermore, neutral Cu(I) complexes 1b-3b show better luminescence in comparison to cationic Cu(I) complexes 1a-3a at room temperature, and temperature variations from 99 K to 298 K result in changing photoluminescence to some extent, which partly agrees with the related calculation results. In these cationic and neutral Cu(I) complexes, the maximum phosphorescent lifetime and quantum yield reach respectively 137 mu s and 42% at room temperature. Moreover, cationic and neutral Cu(I) complexes are utilized to fabricate the monochromatic LEDs, showing favorable electroluminescence with the maximum EQE of 7.10%.

Automated summary

A series of cationic and neutral mononuclear Cu(I) complexes were synthesized and characterized, with their structures and properties showing changes under temperature variations. The neutral Cu(I) complexes exhibit better luminescence performance and are utilized in the fabrication of LEDs with favorable electroluminescence.