A theoretical investigation on the metal–metal interaction in a series of pyrazolate bridged platinum(II) complexes

• The Pt–Pt interactions on excited states have been investigated.
• The Pt–Pt interaction is assessed by bond order and orbital compositions.
• The Pt–Pt bond contraction is much larger than many reported complexes.
• With the Pt–Pt interaction strengthened, the quantum yield will decrease.

Five pyrazolate bridged platinum(II) complexes have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). In contrast to common pyrazolate bridged platinum(II) complexes, these complexes have same pyrazolate bridged ligand while different cyclometalated C^N ligands. To explore the effects of Pt–Pt interaction on spectra and excited state properties, the ground state, singlet state and triplet state structures have been optimized. The Pt–Pt interaction is assessed by the distance between the two Pt atoms, the Mayer bond order and orbital composition analysis. On the lowest triplet excited state, the intermediate size complex shows PtPt single bond formation and the PtPt bond contraction is much larger than many reported bridged platinum complexes. With the Pt–Pt interaction strengthened, the quantum yield and HOMO–LUMO energy gap will decrease. The complex with the biggest cyclometalated C^N ligand shows great potential applications in the design and synthesis of OLED materials since the complex shows the best performance in the injection and transport of hole and electron.

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