Asymmetric Heteroleptic Ir(III) Phosphorescent Complexes with Aromatic Selenide and Selenophene Groups: Synthesis and Photophysical, Electrochemical, and Electrophosphorescent Behaviors

Abstract

With the aim of evaluating the potential of selenium-containing groups in developing electroluminescent (EL) materials, a series of asymmetric heteroleptic Ir(III) phosphorescent complexes (Ir-Se0F, Ir-Se1F, Ir-Se2F, and Ir-Se3F) have been synthesized by using 2-selenophenylpyridine and one ppy-type (ppy = 2-phenylpyridine) ligand with a fluorinated selenide group. To the best of our knowledge, these complexes represent unprecedented examples of asymmetric heteroleptic Ir(III) phosphorescent emitters bearing selenium-containing groups. Natural transition orbital (NTO) analysis based on optimized geometries of the first triplet state (T) have shown that the phosphorescent emissions of these Ir(III) complexes dominantly show π-π* features of the 2-selenophenylpyridine ligand with slight metal to ligand charge transfer (MLCT) contribution. In comparison with their symmetric parent complex Ir-Se with two 2-selenophenylpyridine ligands, these asymmetric heteroleptic Ir(III) phosphorescent complexes can show much higher phosphorescent quantum yields (Φ) of ca. 0.90. Both the hole- and electron-trapping ability of these Ir(III) phosphorescent complexes can be enhanced by selenophene and fluorinated selenide groups to improve their EL efficiencies. The EL abilities of these asymmetric heteroleptic Ir(III) phosphorescent emitters fall in the order Ir-Se3F > Ir-Se2F > Ir-Se1F > Ir-Se0F. The highest EL efficiencies have been achieved by Ir-Se3F in the solution-processed OLEDs with external quantum efficiency (η), current efficiency (η), and power efficiency (η) of 19.9%, 65.6 cd A, and 57.3 lm W, respectively. These encouraging EL results clearly indicate the great potential of selenium-containing groups in developing high-performance Ir(III) phosphorescent emitters.

Asymmetric Tris-Heteroleptic Cyclometalated Phosphorescent Iridium(III) Complexes: An Emerging Class of Metallophosphors

“…23,24 Later, complex 5 was further designed by using (trifluorophenyl)selenylated ppy ligand and 2-(selenophen-2-yl)pyridine. 34 At room temperature, complex 5 exhibited an intense orange emission at 581 nm (632 nm as the shoulder) with a high PLQY of 0.93 in CH 2 Cl 2 .…”

“…The solution-processed OLED based on complex 5 showed high peak EQE of 19.9%. 34 Recently, three red emissive tris-heteroleptic iridophosphors 6−8 (λ PL of ∼620 nm) were reported by incorporating only one dimesitylboranyl moiety into the nitrogen heterocyclic ligand (Figure 3a). 35 These emitters not only exhibited enhanced electron transport abilities but also showed improved PLQYs (0.76 for 6, 0.96 for 7, 0.35 for 8) in the doped films.…”

Preparation via a NHC Dimer Complex, Photophysical Properties, and Device Performance of Heteroleptic Bis(tridentate) Iridium(III) Emitters

“…Furthermore, their emissive properties can be governed by combining different classes of ligands at the coordination sphere of the metal center . The focus has mainly centered on compounds bearing three bidentate three-electron-donor ligands (3b) of two or three different types: i.e., molecules [3b + 3b + 3b′] or [3b + 3b′ + 3b′′] . However, they have two main issues: the existence of structural isomers with their own photophysical properties and a high tendency to afford mixtures of compounds resulting from ligand redistribution equilibria .…”

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

“…In this context, selenophenes and their derivatives have been widely studied due to their intrinsic biological activity [22], such as antidepressant [23][24][25][26][27][28], antioxidant [29][30][31][32][33][34][35], anticonvulsant [36,37], antibacterial [38], antitumor [39][40][41][42][43][44][45][46][47], antinociceptive [48], hepatoprotective [49,50] and antiapoptotic agents [51]. Besides, they have also played an important role in the materials science field, being used to build organic light emitting diodes (OLEDs) [52][53][54][55][56][57][58], organic field effect transistors (OFETs) [59][60][61][62][63][64][65][66][67][68]…”