Platinum(II) Dihalide Complexes with 9‑Arsafluorenes: Effects of Ligand Modification on the Phosphorescent Properties

9-Arsafluorenes, which can be easily and safely synthesized, are promising candidates as ligands for solid-state phosphorescent complexes due to their rigidity and bulkiness. The methyl group of 9-methyl-9-arsafluorene was readily converted to various substituents, and the platinum­(II) dihalide complexes with the obtained 9-arsafluorenes were synthesized. The geometry of the platinum­(II) dihalide complexes was dependent on the induced substituent and the halogen. The trans isomers showed intense phosphorescence, while no emission was observed in the cis isomers. The mechanisms of the different emission behaviors were elucidated by diffuse reflection spectra and theoretical calculations. Among the emissive trans complexes, the substituent of the arsafluorene and the halogen played a key role in the emission intensity.