Emission Enhancement by Intramolecular Stacking between Heteroleptic Iridium(III) Complex and Flexibly Bridged Aromatic Pendant Group

Abstract

Phosphorescent iridium­(III) complexes suffer from a strong aggregation quenching, limiting their use in solution-processed or crystalline organic light-emitting diodes. Here we report how an intramolecular stacking between a flexibly bridged bulky aromatic pendant group and the core of nonionic heteroleptic complex can be exploited to minimize the negative effects of this drawback. The stacked conformation provides a rigid sterical shielding of the polar molecular surface, improving photoluminescence quantum yield of the complex both in solution and crystalline state.

Using a diphenyl-bi-(1,2,4-triazole) tricarbonylrhenium(i) complex with intramolecular π–π stacking interaction for efficient solid-state luminescence enhancement

“…for heteroleptic mono- and di-nuclear Cu( ii ) complexes 49 and for Ir( i ) complexes with very elaborated structures. 22 In the present work, the intramolecular interaction does not require very bulky ligands 12–18,21,22 or polyphenyl units, 23,24 specially designed to form a protecting cage around the metal ion. Instead, we designed a minimalist ligand.…”

“…It leads to enhanced photoluminescence both in solution and in the crystalline state. 22 For rhenium( i ) complexes, intramolecular π–π interactions between the bipyridine (bpy) ligand and the phenyl rings of the phosphorous ligand of fac -[Re(bpy)(CO) 3 (PR 3 )] + (R = p -MeOPh, p -MePh, Ph, p -FPh, OPh) complexes have been shown to affect their structure, electrochemical behavior and some spectroscopic properties in solution. However, no effect on possible solid-state emission properties has been reported.…”

Study of a phosphorescent cationic iridium(iii) complex displaying a blue-shift in crystals

“…The complex displays different colours in the powder and crystal forms, which may be related to polymorphism. 23,36,38,[73][74][75] The powder XRD pattern displays three undefined humps roughly centered at 10 °, 19 ° and 37 °. The absence of fine peaks demonstrates that the precipitated powder is amorphous.…”

“…The large majority of the cationic iridium(III) complexes display a bathochromic shift in solid state, 17,23,[32][33][34][24][25][26][27][28][29][30][31] whereas only few contributions report iridium(III) complexes displaying a hypsochromic shift. 17,27,40,[32][33][34][35][36][37][38][39] If bathochromic shifts could be easily rationalized with the presence of intermolecular interactions, such as - interactions, 14 blue shifted emission spectra in solid state are less straightforward dealing with neat solid. In addition, the understanding of solid-state emission deals mainly with compounds displaying mechanochromism or piezochromism, which is the property of certain materials to change color by the application of pressure, usually through grinding.…”

Effects of steric encumbrance of iridium(iii) complex core on performance of solution-processed organic light emitting diodes

“…Such approach has been previously applied to acquire solutionprocessable emitters with a solely purpose to provide a sterical barrier between complex molecules. 29 The synthesis was performed using m-chloro-bridged iridium(III) complex dimers 1a 30 and 1b 31 as the starting materials. The introduction of the third cyclometalating ligand was accomplished by utilizing the procedure by Colombo et al, 32 which strictly yields triscyclometalated complexes with a fac-structural conguration.…”