Electronic spectra and photophysics of platinum(II) complexes with α-diimine ligands. Mixed complexes with halide ligands

Emission properties have been studied for a series of compounds of the formula (L_2)PtC1_2, where L_2 is N,N,N',N'-tetramethylethylenediamine, 2,2'-bipyridine (bpy), 4,4'-Me_2bpy, 5,5'-Me_2bpy, 4,4'-(t-Bu)_2bpy, 3,3'-(CH_3OCO)_2bpy, and 1,10-phenanthroline, and also for the compound Pt(bpy)I_2. Most of them exhibit orange to red luminescence from a triplet ligand-field (^3LF) state, both as solids and in glassy solution. These emissions are very broad (fwhm 2300-3400 cm^(-1) at 10 K) and structureless and are strongly Stokes-shifted from absorption. The two exceptions are the solid "red" form of Pt(bpy)Cl_2, which exhibits a relatively narrow (fwhm 1050 cm^(-1) at 10 K), vibronically structured (Δν ~ 1500 cm^-1)) red emission, and Pt(3,3'-(CH_3OCO)_2bpy)Cl_2, which exhibits a broad (fwhm 2500 cm^(-1) at 10 K) but structured (Δν ~1300 cm^(-1)) orange emission. Both of these emissions are assigned to triplet metal-to-ligand charge-transfer (^3MLCT) excited states. For the former compound, a linear-chain structure has destabilized a dσ*(d_(z^2)) level, yielding a dσ* → π*(bpy) state as the lowest energy excited state, while for the latter, the strongly electron-withdrawing substituents have stabilized a bpy π* level, yielding a dσ* → π*(bpy) state as the lowest energy excited state. The relative energies of the various types of excited states, including ligand 3_(ππ*) states, are discussed in detail. The crystal structures of Pt(5,5'-Me_2bpy)Cl_2 (monoclinic Cc, Z = 4, a = 13.413(7) Å, b = 9.063(4) Å, c = 12.261(9) Å, 0 = 121.71(6)') and Pt(3,3'-(CH_3OCO)_2bpy)Cl_2 (triclinic P1, Z = 2, a = 7.288(2) Å, b = 9.932(3) Å, c = 11.881(5) Å, α = 98.04(3)°, β = 103.56(3)°, γ = 106.54(3)°) are reported

Electronic spectra and photophysics of platinum(II) complexes with α-diimine ligands. Mixed complexes with halide ligands

Emission properties have been studied for a series of compounds of the formula (L_2)PtC1_2, where L_2 is N,N,N',N'-tetramethylethylenediamine, 2,2'-bipyridine (bpy), 4,4'-Me_2bpy, 5,5'-Me_2bpy, 4,4'-(t-Bu)_2bpy, 3,3'-(CH_3OCO)_2bpy, and 1,10-phenanthroline, and also for the compound Pt(bpy)I_2. Most of them exhibit orange to red luminescence from a triplet ligand-field (^3LF) state, both as solids and in glassy solution. These emissions are very broad (fwhm 2300-3400 cm^(-1) at 10 K) and structureless and are strongly Stokes-shifted from absorption. The two exceptions are the solid "red" form of Pt(bpy)Cl_2, which exhibits a relatively narrow (fwhm 1050 cm^(-1) at 10 K), vibronically structured (Δν ~ 1500 cm^-1)) red emission, and Pt(3,3'-(CH_3OCO)_2bpy)Cl_2, which exhibits a broad (fwhm 2500 cm^(-1) at 10 K) but structured (Δν ~1300 cm^(-1)) orange emission. Both of these emissions are assigned to triplet metal-to-ligand charge-transfer (^3MLCT) excited states. For the former compound, a linear-chain structure has destabilized a dσ*(d_(z^2)) level, yielding a dσ* → π*(bpy) state as the lowest energy excited state, while for the latter, the strongly electron-withdrawing substituents have stabilized a bpy π* level, yielding a dσ* → π*(bpy) state as the lowest energy excited state. The relative energies of the various types of excited states, including ligand 3_(ππ*) states, are discussed in detail. The crystal structures of Pt(5,5'-Me_2bpy)Cl_2 (monoclinic Cc, Z = 4, a = 13.413(7) Å, b = 9.063(4) Å, c = 12.261(9) Å, 0 = 121.71(6)') and Pt(3,3'-(CH_3OCO)_2bpy)Cl_2 (triclinic P1, Z = 2, a = 7.288(2) Å, b = 9.932(3) Å, c = 11.881(5) Å, α = 98.04(3)°, β = 103.56(3)°, γ = 106.54(3)°) are reported

Lowest Electronic Excited States of Platinum(II) Diimine Complexes

Absorption and emission spectra of Pt(diimine)L_2 complexes (diimine = 2,2‘-bipyridine (bpy) or 4,4‘-dimethyl-2,2‘-bipyridine (dmbpy); L = pyrazolate (pz-), 3,5-dimethylpyrazolate (dmpz-), or 3,4,5-trimethylpyrazolate (tmpz-)) have been measured. Solvent-sensitive absorption bands (370−440 nm) are attributed to spin-allowed metal-to-ligand charge-transfer (^1MLCT) transitions. As solids and in 77 K glassy solution, Pt(bpy)(pz)_2 and Pt(dmbpy)(pz)_2 exhibit highly structured emission systems (λ_(max)≈ 494 nm) similar to those of the diprotonated forms of these complexes. The highly structured bands (spacings 1000−1400 cm^(-1)) indicate that the transition originates in a diimine-centered ^3(π→π*) (^3LL) excited state. The intense solid-state and 77 K glassy solution emissions from ^3MLCT[d(Pt)→π*(bpy)] excited states of complexes with dmpz- and tmpz- ligands occur at longer wavelengths (λ_(max) = 500−610 nm), with much broader vibronic structure. These findings are consistent with increasing electron donation of the pyrazolate ligands, leading to a distinct crossover from a lowest ^3LL to a ^3MLCT excited state