Unusual Excimer/Dimer Behavior of a Highly Soluble C,N Platinum(II) Complex with a Spiro-Fluorene Motif

In this work, we introduce a spiro-fluorene unit into a phenylpyridine (CN)-type ligand as a simple way to deplanarize the structure and increase the solubility of the final platinum(II)complex. Using a spiro-fluorene unit, orthogonal to the main coordination plane of the complex, reduces intermolecular interactions, leading to increased solubility but without significantly affecting the ability of the complex to form PtPt dimers and excimers. This approach is highly important in the design of platinum(II) complexes, which often suffer from low solubility due to their mainly planar structure, and offers an alternative to the use of bulky alkyl groups. The nonplanar structure is also beneficial for vacuum-deposition techniques as it lowers the sublimation temperature. Importantly, there are no sp(3) hybridized carbon atoms in the cyclometalating ligand that contain hydrogens, the undesired feature that is associated with the low stability of the materials in OLEDs. The complex displays high solubility in toluene, similar to 10 mg mL(-1), at room temperature, which allows producing solution-processed OLEDs in a wide range of doping concentrations, 5-100%, and EQE up to 5.9%, with a maximum luminance of 7400 cd m(-2). Concurrently, we have also produced vacuum-deposited OLEDs, which display luminance up to 32 500 cd m(-2) and a maximum EQE of 11.8%

Automated summary

In this work, we introduced a spiro-fluorene unit into a phenylpyridine (CN)-type ligand to deplanarize the structure and increase the solubility of a platinum(II) complex. This approach is highly important in the design of platinum(II) complexes to overcome low solubility and offers an alternative to using bulky alkyl groups. The nonplanar structure is also beneficial for vacuum-deposition techniques and eliminates the undesired feature of containing sp(3) hybridized carbon atoms.