Regiospecific Quenching of a Photoexcited Platinum(II) Complex at Acidic and Basic Sites

Assessing the Character of the C6F5 Ligand from the Electrochemical and Photophysical Properties of [Ni(C6F5)2(N∧N)] Complexes

Organonickel complexes containing α-diimine ligands [Ni(C6F5)2(N∧N)] (N∧N = 2,2'-bipyridine (bpy), 2,9-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), dipyrido[3,2-a:2',3'-c]phenazine (dppz), 1,4-bis(isopropyl)-1,4-diazabutadiene (iPr-DAB), and 1,4-bis(2,6-dimethylphenyl)-1,4-diazabutadiene (Xyl-DAB) were prepared and studied structurally, spectroscopically, and electrochemically. Their molecular structures from single-crystal X-ray diffraction show near-perfect square planar Ni(II) coordination except in the case of dmphen. Primary reversible electrochemical reductions in the range from -1 to -2 V vs ferrocene/ferrocenium couple lead to mainly diimine-localized radical anion complexes, while secondary reductions in the range from -2 to -2.5 V lead to dianion complexes, as shown through spectroelectrochemistry. Irreversible metal-centered oxidations at around 0.7 V result in rapid aryl-aryl reductive elimination and formation of decafluorobiphenyl. No photoluminescence was detected for the complexes containing chromophoric α-diimine ligands at room temperature. At 77 K in frozen glassy 2-Me-THF matrices, weak photoluminescence was detected for the dmphen and tmphen derivatives, with broad emission bands peaking around 570 nm. All results are rationalized with the support of (TD-)DFT calculations, highlighting the role of the C6F5 ligand in different systems.

A Platinum-Dithiolene Monoanionic Salt Exhibiting Multiproperties, Including Room-Temperature Proton-Dependent Solution Luminescence

The platinum salt C[PtL2], where C = [(R)-Ph(Me)HC*-NMe3](+) and [PtL2](-) = radical monoanion based on [4', 5': 5, 6][1, 4]dithiino[2,3-b]quinoxaline-1',3'dithiolato, shows a variety of properties both in solution and in the solid state thanks to the electronic and/or structural features of the ligand. The complex crystallizes in the chiral space group P1 due to the presence of the enantiopure cation (R)-Ph(Me)HC*-NMe3(+), and it shows paramagnetic behavior relatable to the [PtL2](-) radical monoanion. This anionic complex is redox active and shows a strong near-infrared absorbance peak at 1085 nm tunable with the oxidation state of the complex. This complex exhibits a proton-dependent emission at 572 nm in solution at room temperature. The excitation band corresponds to the HOMO-1 (π-orbitals of the S2C2S2 system) → LUMO (π-orbitals of the quinoxaline and benzene-like moieties) transition suggesting that emission is mainly ligand centered in character. The luminescent properties are highly unusual, since the emission falls well above the energy of the lowest energy absorption (anti-Kasha behavior). Joint experimental and density functional theory (DFT) and time-dependent DFT studies are discussed to provide a satisfactory structure/property relationship.