Efficient deep-red light-emitting electrochemical cells based on a perylenediimide-iridium-complex dyad

Abstract

A two-layer light-emitting electrochemical cell device based on a new perylenediimide-iridium-complex dyad is presented emitting in the deep-red region with high external quantum efficiencies (3.27%).Light-emitting electrochemical cells (LECs) based on ionic transition-metal complexes are among the simplest types of organic light-emitting devices (OLEDs). Their configuration mainly consists of an amorphous film of the active compound placed in between two electrodes.1 In spite of the disadvantages of LECs compared to OLEDs, like long turn-on time, shorter lifetimes, and lower efficiencies, LECs offer the advantage of using a less-reactive cathode material (aluminium instead of calcium or magnesium) and hence do not require stringent protection from environmental oxygen and water.Currently, the most widely used compounds in singlecomponent LEC devices are based on homoleptic complexes of Ru(II) and biscyclometalated heteroleptic complexes of Ir(III) whose positive charge is balanced by large negative counterions such as hexafluorophosphate.1 Their use in LECs is mainly due to their high phosphorescence emission quantum yields, short excited triplet state lifetimes and photochemical stability.2,3 However, complexes which give rise to efficient devices are not available for the deep-red region. This can be fulfilled by perylenediimides (PDIs), which present an exceptional photochemical stability, are strong light absorbers in the visible and show high fluorescence quantum yields, [4][5][6] which makes them interesting candidates for OLEDs. However, PDIs are poor hole conductors, which makes them unsuitable for single-component type devices. LECs additionally rely on the presence of mobile ions, and hence the emitting species must be compatible on the nanoscale with charged species. Single-layer LECs using PDI as n-type emissive material and lithium triflate have been recently reported showing red emission at high applied bias (+8 V). 7A polyimide LEC incorporating perylene and tri(ethylene oxide) moieties has been also studied showing a much more intensified electroluminescence than the respective polyimide LED. 8Taking into account the previous considerations, we decided to look for a synergistic collaboration between an ionic iridium(III) complex (that functions as the hole conductor and high phosphorescence emitter) and a PDI red fluorescent emitter (that functions as the electron conductor), in an attempt to achieve a high efficiency in the system. Moreover, the covalent linking of the moieties should increase the thermal stability, while avoiding phase separation processes. With this idea in mind, we have synthesized a new dyad consisting of a PDI derivative linked with an ionic iridium complex. The new dyad 1, see Scheme 1, is used as the single active component in a double-layer LEC device, showing efficient deep-red electroluminescence.The synthesis of the [PDI-iridium]PF 6 dyad 1 is outlined in Scheme 1. Condensation of tetra-tert-octylphenoxy monoanhydride monoimide 2 with 5-amino-1,10-phenanthroline 9 us...

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

“…Su et al used a fluorescent dye in an Ir-iTMC to generate efficient red electroluminescence reaching 19 cd A À1 and 21.3 lm W À1 . [187] In a similar approach, Costa et al [191,192] showed the beneficial effect of anchoring a perylenediimide (PDI) red fluorescent emitter to an ionic iridium(III) complex (45, Figure 29). [192] The EL spectrum of the LEC incorporating 45 is attributable to the PDI moiety (l max = 634 nm, CIE coordinates x = 0.654; y = 0.344).…”

“…[187] In a similar approach, Costa et al [191,192] showed the beneficial effect of anchoring a perylenediimide (PDI) red fluorescent emitter to an ionic iridium(III) complex (45, Figure 29). [192] The EL spectrum of the LEC incorporating 45 is attributable to the PDI moiety (l max = 634 nm, CIE coordinates x = 0.654; y = 0.344). They also showed in a separate study that triplet radiationless pathways occur through the PDI moiety [191] but, surprisingly, LECs using such an Ir-iTMC-PDI complex showed external quantum efficiencies as high as 3.3 %.…”

Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives

“…There has been one PDI/iridium complex dyad reported in the literature by Ortí and Gierschner, in which the metal is complexed by one PDI-linked 1,10-phenanthroline and two 2-phenylpyridine ligands (6,25). Upon selective excitation of the PDI moiety, the dyad emits with a quantum yield of Φ F ¼ 0.55, reduced from Φ F ¼ 0.86 of the PDI model compound, a decrease which the authors attribute to SO-ISC induced by the iridium atom (6).…”

Step-by-step self-assembled hybrids that feature control over energy and charge transfer

“…Moreover, PDIs are strongly fluorescent chromophores possessing fluorescence quantum yields close to unity, with emission maxima that range from 500-700 nm (35). PDIs have been extensively used as light absorbers, energy-transfer agents, and charge carriers (36,37) either being covalently or noncovalently linked to other photo-and electroactive molecules like porphyrins (38,39), phthalocyanines (40)(41)(42)(43)(44)(45), fullerenes (46)(47)(48), and so on (49).…”