Phosphorescent iridium(iii) complexes: toward high phosphorescence quantum efficiency through ligand control

Abstract

Phosphorescent Ir(III) complexes attract enormous attention because they allow highly efficient electrophosphorescence. In pursuing the development of Ir(III) complexes during the last decade, significant progress has been made in terms of the colour-tunability, thermal- and photo-stability, phase homogeneity, and phosphorescence efficiency. By far, extensive synthetic efforts have been focused on the molecular design of ligands to achieve a wide range of phosphorescence colour that is compatible with organic light-emitting device (OLED) applications. In contrast, less has been known about a collective structure-property relationship for phosphorescence quantum efficiency. In fact, a few rule-of-thumbs for high phosphorescence quantum efficiency have been occasionally reported, but a collective rationale is yet to be investigated. In this article, we provide a comprehensive review of 8 different methods reported so far to achieve high phosphorescence quantum efficiency from Ir(III) complexes. The methods included herein are limited to the cases of intramolecular controls, and thus are discussed in terms of variations in ligand structures: (1) geometric isomer control, (2) rigid structure and restricted intramolecular motion, (3) larger mixing of 1MLCT and 3LC states, (4) de-stabilizing a thermally accessible non-emissive state, (5) introducing dendrimer structures, (6) control in substituents of ligands, (7) confining the phosphorescent region of a mixed ligand Ir(III) complex and (8) sensitized phosphorescence by using attached energy donors. Each method is closely related to intramolecular excited state interactions, which strongly affect radiative or non-radiative transitions. A comprehensive understanding of these methods leads us to conclude that the modulation in ligand structures has a profound effect on both the phosphorescence colour and phosphorescence quantum efficiency. Thus, the judicious selection of ligand structures and their chelate disposition should be considered before synthesis. We expect that the guidelines for attaining a high phosphorescence efficiency, summarized in this Perspective, would be helpful in developing highly phosphorescent Ir(III) complexes.

Hypoxia-specific ultrasensitive detection of tumours and cancer cells in vivo

“…All of these limitations compromise the ability of these probes to detect hypoxia in the tumour. On the other hand, phosphorescent transition metal complexes have shown to be very effective in imaging and sensing the oxygen level in biological samples 19,20 , given the high sensitivity to oxygen, tunable excitation and emission wavelength and high luminescent quantum yields 21,22 . However, the phosphorescent transition metal imaging probes have poor biodistribution and pharmacokinetic profiles for tumour imaging due to nonspecific uptake by normal tissues, binding to plasma proteins and rapid renal clearance, limiting their ability to differentiate hypoxic and normoxic conditions 23 .…”

Preparations of iridium complexes containing phenanthroline ancillary ligands and electrical properties of cationic iridium‐based light‐emitting electrochemical cells

“…Other ligands are called ancillary ligands if their ligand structure is different from that of the cyclometalating ligand or if Ir is not bonded to C and N in one ligand, and they are called N^N ligands. [13] Archetype LECs using [iridium(2-phenylpyridine) 2 (1,10-phenanthroline)]PF 6 present yellow emission color and rather poor performance. [14] In this study, two types of phenanthrolinederivated ancillary ligands were used to investigate the effect of methyl functional groups as electron donating groups.…”

“…[13] Iridium trichloride hydrate, 2-phenylpyridine, and two types of phenanthroline derivates (5-methyl-1,10-phenanthroline and 5,6-dimethyl-1,10-phenanthroline) were purchased from Aldrich.…”

“…It provides that transition metal complexes based on iridium core metal exhibit efficient roomtemperature phosphorescence because they have high phosphorescence quantum efficiency, good photo and thermal stability, facile emission color tuning through changing ligands structure, large cross section for the exciton formation. [13] In this study, iridium complex with phenanthroline as the ancillary ligands has been prepared, and their electrochemical properties have been investigated. Single component luminous layer-based LECs with the charged complex as conducting and EL material sandwiched between indium tin oxide (ITO) and aluminum (Al) were fabricated: ITO/PEDOT:PSS/[iridium (2-phenylpyridine) 2 (5-methyl-1,10-phenanthroline)]PF 6 /Al and ITO/PEDOT:PSS/[iridium(2-phenylpyridine) 2 (5,6-dimethyl-1,10-phenanthroline)]PF 6 /Al.…”

Compostos de coordenação de Ir(III), Re(I) e Ru(II) para aplicações em dispositivos moleculares

“…O uso estratégico de compostos de coordenação fosforescentes nas camadas ativas desses dispositivos pode levar a um aproveitamento de 100% dos éxcitons gerados, tornandoos ainda mais eficiente [13,30,36,37,60,61]. Dentre esses compostos, os complexos de Ir(III) possuem características únicas e vantajosas, resultantes do alto acoplamento spinórbita e forte interação eletrônica entre metal-ligante [13,36,37,[61][62][63][64][65], por exemplo:…”