reported in Table 5. Indeed, when calculating the triplet spin-orbit sub-levels by
applying SOC correction at their optimized geometries the stabilization of the
minima never exceeds 0.1 eV as illustrated by the results obtained for Re(I) carbonyl α-diimine complexes discussed in the next section.
The presence of MC states situated well above the MLCT/XLCT/LC emissive
states, needing strong structural stabilizing out-of-plane deformation for being
populated, ensures the effectiveness of luminescence in this class of Pt
(II) molecules. This study has shown that the usual oversimplified picture of a
single T 1 triplet state for explaining luminescent properties of the Pt(II) square
planar complexes is far from realistic.
4.3 Luminescence of Re(I) Complexes
In the following example, emissive properties of [ReX(CO) 3 (bpy)] (X ¼ Cl, Br, I;
bpy ¼ 2,2
0 -bipyridine) complexes (Scheme 2) have been interpreted on the basis of
TD-DFT T n ! S 0 transition energies calculated at the fully optimized geometries of
the six low-lying singlet and triplet excited states and corrected by SOC
(Table 6) [121].
The “spin-free” and “spin-orbit” excited states reported in Table 6 are of mixed
either MLCT/XLCT (X ¼ Cl and Br; complexes 11 and 12) or XLCT/MLCT
(X ¼ I; complex 13) character and potentially emissive after absorption at
Table 5 TD-DFT/B3LYP vertical T n ! S 0 transition energies (in eV) and corresponding emission wavelengths (in nm) of complexes 6 to 10 depicted in Scheme 4 (adapted with permission
from Gourlaouen and Daniel [75] Copyright 2014 Royal Society of Chemistry)
State
Vertical T n ! S 0
transition energy (eV)
Emission
wavelength (nm)
[Pt (bpy)Cl 2 ] 6
T 1 MC
À0.36
–
T 2 MC/XLCT
0.92
1,355
[Pt (tpy)Cl]
+ 8
T 1 MC
0.41
3,012
T 2 MLCT/LC
1.92
645
[Pt (ppy)Cl 2 ]
À 7
T 1 MLCT/XLCT/LC
2.34
530
T 2 MC/LC
2.28
544
T 3 MC
2.33
531
T 4 MC/LMCT/MLCT
2.41
515
[Pt (phbpyH)Cl] 9
T 1 MLCT/LC
2.02
613
T 2 MC
0.43
2,852
S 1 MLCT/LC
2.35
527
T 3 MLCT/XLCT/LC
2.71
458
[Pt (dpybR)Cl] 10
(R ¼ CH 3 )
T 1 MLCT/LC/XLCT
2.42
513
T 2 MLCT/LC/XLCT
2.48
500
T 3 MC
0.98
1,271
T 4 MC
1.47
846
Absorption Spectroscopy, Emissive Properties, and Ultrafast Intersystem. . .
399
applying SOC correction at their optimized geometries the stabilization of the
minima never exceeds 0.1 eV as illustrated by the results obtained for Re(I) carbonyl α-diimine complexes discussed in the next section.
The presence of MC states situated well above the MLCT/XLCT/LC emissive
states, needing strong structural stabilizing out-of-plane deformation for being
populated, ensures the effectiveness of luminescence in this class of Pt
(II) molecules. This study has shown that the usual oversimplified picture of a
single T 1 triplet state for explaining luminescent properties of the Pt(II) square
planar complexes is far from realistic.
4.3 Luminescence of Re(I) Complexes
In the following example, emissive properties of [ReX(CO) 3 (bpy)] (X ¼ Cl, Br, I;
bpy ¼ 2,2
0 -bipyridine) complexes (Scheme 2) have been interpreted on the basis of
TD-DFT T n ! S 0 transition energies calculated at the fully optimized geometries of
the six low-lying singlet and triplet excited states and corrected by SOC
(Table 6) [121].
The “spin-free” and “spin-orbit” excited states reported in Table 6 are of mixed
either MLCT/XLCT (X ¼ Cl and Br; complexes 11 and 12) or XLCT/MLCT
(X ¼ I; complex 13) character and potentially emissive after absorption at
Table 5 TD-DFT/B3LYP vertical T n ! S 0 transition energies (in eV) and corresponding emission wavelengths (in nm) of complexes 6 to 10 depicted in Scheme 4 (adapted with permission
from Gourlaouen and Daniel [75] Copyright 2014 Royal Society of Chemistry)
State
Vertical T n ! S 0
transition energy (eV)
Emission
wavelength (nm)
[Pt (bpy)Cl 2 ] 6
T 1 MC
À0.36
–
T 2 MC/XLCT
0.92
1,355
[Pt (tpy)Cl]
+ 8
T 1 MC
0.41
3,012
T 2 MLCT/LC
1.92
645
[Pt (ppy)Cl 2 ]
À 7
T 1 MLCT/XLCT/LC
2.34
530
T 2 MC/LC
2.28
544
T 3 MC
2.33
531
T 4 MC/LMCT/MLCT
2.41
515
[Pt (phbpyH)Cl] 9
T 1 MLCT/LC
2.02
613
T 2 MC
0.43
2,852
S 1 MLCT/LC
2.35
527
T 3 MLCT/XLCT/LC
2.71
458
[Pt (dpybR)Cl] 10
(R ¼ CH 3 )
T 1 MLCT/LC/XLCT
2.42
513
T 2 MLCT/LC/XLCT
2.48
500
T 3 MC
0.98
1,271
T 4 MC
1.47
846
Absorption Spectroscopy, Emissive Properties, and Ultrafast Intersystem. . .
399