16 Luminescent Materials for Organic Light-Emitting Diodes
581
16.3.2 Phosphorescent Emitters Based
on Organoplatinum(II) Complexes
Along with organoiridium(III) complexes, platinum complexes exhibiting efficient
room-temperature phosphorescent emission have been frequently reported for OLED
applications. In most cases, practical emitters are organoplatinum(II) complexes
bearing cyclometalated ligands such as bidentate CˆN and CˆC, tridentate CˆNˆN
and NˆCˆN, and a tetradentate NˆCˆCˆN. The d
8 electronic configuration of platinum allows for obtaining stable square planar structures such as Pt(CˆN)(LˆX)
(Brooks et al. 2002d), Pt(CˆC)(LˆX) (Unger et al. 2010), Pt(NˆCˆN)X (Williams
et al. 2003), Pt(CˆNˆN)X (Lu et al. 2004), and Pt(NˆCˆCˆN) (Fukagawa et al. 2012)
(the general structures, shown in Fig. 16.18). As is the case with phosphorescent
organoiridium(III) emitters, strong spin–orbit coupling is induced by the platinum
atom to make the mixing of the singlet and triplet excited state efficient to reduce
the spin-forbidden nature. So, effective perturbation between the metal center and
the cyclometalated ligand through the metal–sp
2 -carbon bonding plays a significant
role in obtaining efficient phosphorescent emission, usually through
3 MLCT and
metal-perturbed
3
π–π* transitions. In this term, as the cyclometalated ligands join
in the electronic transition, they are also important to determine the emission color.
In this section, phosphorescent organoplatinum(II) complexes for OLED applications are reviewed, focusing the attention on their structures. One of the characteristic features of organoplatinum(II) complexes is excimer or aggregate formation
through metal–metal and/or π-based intermolecular stacking interactions caused by
Fig. 16.18 General structures of organoplatinum(II) complexes bearing bidentate (CˆN and CˆC),
tridentate (NˆCˆN and CˆNˆN), and tetradentate (NˆCˆCˆN) ligands. LˆX and X represent an anionic
bidentate ligand and an anionic monodentate one, respectively. The substituent Ar represents an
aryl group
581
16.3.2 Phosphorescent Emitters Based
on Organoplatinum(II) Complexes
Along with organoiridium(III) complexes, platinum complexes exhibiting efficient
room-temperature phosphorescent emission have been frequently reported for OLED
applications. In most cases, practical emitters are organoplatinum(II) complexes
bearing cyclometalated ligands such as bidentate CˆN and CˆC, tridentate CˆNˆN
and NˆCˆN, and a tetradentate NˆCˆCˆN. The d
8 electronic configuration of platinum allows for obtaining stable square planar structures such as Pt(CˆN)(LˆX)
(Brooks et al. 2002d), Pt(CˆC)(LˆX) (Unger et al. 2010), Pt(NˆCˆN)X (Williams
et al. 2003), Pt(CˆNˆN)X (Lu et al. 2004), and Pt(NˆCˆCˆN) (Fukagawa et al. 2012)
(the general structures, shown in Fig. 16.18). As is the case with phosphorescent
organoiridium(III) emitters, strong spin–orbit coupling is induced by the platinum
atom to make the mixing of the singlet and triplet excited state efficient to reduce
the spin-forbidden nature. So, effective perturbation between the metal center and
the cyclometalated ligand through the metal–sp
2 -carbon bonding plays a significant
role in obtaining efficient phosphorescent emission, usually through
3 MLCT and
metal-perturbed
3
π–π* transitions. In this term, as the cyclometalated ligands join
in the electronic transition, they are also important to determine the emission color.
In this section, phosphorescent organoplatinum(II) complexes for OLED applications are reviewed, focusing the attention on their structures. One of the characteristic features of organoplatinum(II) complexes is excimer or aggregate formation
through metal–metal and/or π-based intermolecular stacking interactions caused by
Fig. 16.18 General structures of organoplatinum(II) complexes bearing bidentate (CˆN and CˆC),
tridentate (NˆCˆN and CˆNˆN), and tetradentate (NˆCˆCˆN) ligands. LˆX and X represent an anionic
bidentate ligand and an anionic monodentate one, respectively. The substituent Ar represents an
aryl group