Trinuclear Platinum(II) 4,6-Diphenyl-2,2‘-bipyridyl Complex with Bis(diphenylphosphinomethyl)phenylphosphine Auxiliary Ligand: Synthesis, Structural Characterization, and Photophysics

A trinuclear cyclometalated Pt(II) 4,6-diphenyl-2,2‘-bipyridyl complex with bis(diphenylphosphinomethyl)phenylphosphine bridging ligand ([4-Ph(C∧N∧N)Pt]3dpmp) has been synthesized and characterized. It exhibits a
broad electronic absorption band from 400 to 600 nm because of its intramolecular Pt···Pt interactions that have
been revealed by X-ray crystal structure analysis. This complex shows strong red emission in acetonitrile at room
temperature and 77 K. The electronic and emission spectra exhibit concentration and temperature dependence.
With increased concentrations, the UV band of the absorption spectrum gradually decreases and broadens,
accompanied by an increase of the 1[dσ*,π*] band between 400 and 600 nm. For emission spectra, the 550 nm
band that originates from the mononuclear platinum(II) component gradually decreases with increased concentrations,
while the band at ∼700 nm that corresponds to the 3[dσ*,π*] state increases. In addition, the UV−vis and emission
spectra exhibit temperature and viscosity-dependence. The concentration-, temperature-, and viscosity-dependent
characteristics indicate a conformational change of the complex arising from the rotation along the oligophosphine
axis. This complex exhibits broad, positive, and strong transient difference absorption bands from the near-UV to
near-IR spectral region. However, because of the increased ground-state absorption in the visible region, the
nonlinear transmission of this trinuclear platinum complex decreases.