Induced Aggregation of AIE‐Active Mono‐Cyclometalated Ir(III) Complex into Supramolecular Branched Wires for Light‐Emitting Diodes

Abstract

Aggregation-induced emission (AIE) is commonly observed in irregular bulk form. Herein, unique aggregation properties of an AIE-active complex into branched supramolecular wires are reported for the first time. Mono-cyclometalated Ir(III) complex shows in-plane J-aggregation at the air-water interface owing to the restriction of intramolecular vibration of bidentate phenylpyridinato and intramolecular rotations of monodentate triphenylphosphine ligands at air-water interface. As a consequence, a large enhancement of luminescence comparable to the solid state is obtained from the monolayers of supramolecular wires. This unique feature is utilized for the fabrication of light-emitting diodes with low threshold voltage using supramolecular wires as active layer. This study opens up the need of ordered assembly of AIE complexes to achieve optimal luminescence characteristics.

Origin of Intense Luminescence from Supramolecular 2D Molecular Crystals

“…These ex situ AFM observations are in-line with our previous report at different surface pressures. [21] A constant thickness of 4.8 nm along the (20) reflection in the q z profile (Table S1, Supporting Information) corroborates with the extracted average height profiles from the AFM images of the transferred monolayer at different surface pressures (Figures S2,S3, Supporting Information).…”

“…[17,18] In most of the cases, AIE strategy relies in storing excited electrons in the long-lived triplet states. [19][20][21][22][23][24] Efficient phosphorescence may be achieved by effective intersystem crossings (ISC) through small energy gap (ΔE ST ) between singlet-triplet levels and mixing of the singlet and triplet states by strong spin-orbit coupling (SOC). [25][26][27][28] However, the rational design of small ΔE ST and enhanced SOC are rather complex considering the dependency on molecular conformations and electronic configurations within 2D crystals.…”

“…Earlier we introduced a promising strategy to fabricate 2D crystals of AIEactive cyclometalated Ir(III) complex, [Ir(ppy)(PPh 3 ) 2 (H)(Cl)] (Cyclo-Ir) at the flat water surface having small roughness. [18][19][20][21] Molecular thick stable 2D crystals with micron length were fabricated in a controllable way. A marked enhancement of photoluminescence (PL) in comparison to the solution phase was observed from the confined 2D crystals.…”

Aggregation‐Induced Electrochemiluminescence by Metal‐Binding Protein Responsive Hydrogel Scaffolds

“…In contrast to ACQ agents, the low luminescent AIE molecules, i.e., AIEgens, can be conjugated together, resulting in significantly enhanced luminescence. Such a phenomenon is initially reported for organic compounds,8b complexes, or polymers containing special rotor‐like structures, but now has been observed for metallic nanoclusters (NCs). In this aspect, Xie's group has intensively reported the AIE by different NCs .…”

Aggregation‐induced Phosphorescence Enhancement in IrIII Complexes

“…For this latter case, maxima in the range λ em =441–593 nm were recorded. Moreover, compound 27 was employed for the preparation of supramolecular branched wires suitable for the fabrication of OLED devices …”