Aggregation-Enhanced Emission in a Red Cu(I) Emitter with Quantum Yield >99%

Abstract

It is a significant challenge to achieve a high photoluminescence quantum yield of Cu(I) complexes, particularly for red Cu(I) emitters, because of their considerable reorganization energy and weak spin−orbit coupling. Herein, we report a red phosphorescent cyclic trinuclear Cu(I) complex (denoted as 1), which was formed by reacting alkyl-substituted pyrazole ligands (4-isobutyl-3,5-dimethyl-1H-pyrazole) with in situ generated Cu(I) ions. Complex 1 was nonemissive in a pure tetrahydrofuran (THF) solution, whereas it emitted intense red light when its molecules were aggregated by adding water to the THF solution. Near-unity photoluminescence quantum yields were achieved in a mixed solvent of THF/water (f e = vol water / vol water+THF , f e = 90%), poly(methyl methacrylate) films, and in the solid state. Photophysical analysis and theoretical calculations revealed that the excellent photoluminescence performance was due to the aggregation-enhanced emission. In the aggregation state, cuprophilic interactions dominated the excited state, and the restricted movement of alkyl through CH•••C/CH•••π interactions diminished nonradiative transition. A cyclic trinuclear Cu(I) complex was used to fabricate a nondoped organic light-emitting diode (OLED), which is the first instance of such Cu(I) materials.

Ionic Liquids-Driven Cluster-to-Cluster Conversion of Polyhydrido Copper(I) Clusters Cu7H5 to Cu8H6 and Cu12H9

“…The higher-energy absorptions below 350 nm are typical for ligand-centered [π → π*] (dppy ligand) absorption, based on the similar absorption energies with those of the free dppy ligand. The lower-energy shoulder is similar to that observed in the related Cu 3 H and Cu 4 H , ,− suggesting their origin from ligand-to-metal-metal charge transfer (LMMCT) or cluster-centered (CC).…”

“…Comparing the emissions both in the solid state and in solution, a red shift in energy is observed on going from Cu 7 H 5 to Cu 8 H 6 and Cu 12 H 9 (Figure S13), which is consistent with the order of the stronger cuprophilic interactions by single-crystal X-ray analysis. Following previous assignments ,− and in view of the good σ-donating capability of the dppy ligand, the origin of the emissions for three Cu­(I)H clusters is assigned as the triplet ligand-to-metal-metal charge-transfer ( 3 LMMCT) excited state or cluster-centered (CC) modified by metal–metal interactions. The red shift in the emission wavelengths of Cu 7 H 5 to Cu 8 H 6 and Cu 12 H 9 may be ascribed to the stronger cuprophilic interactions, which decreases the energy of the metal-centered acceptor orbitals and gives rise to a lower LMMCT or CC emission energy.…”

Viewing Aggregation-Induced Emission of Metal Nanoclusters from Design Strategies to Applications

“…(iii) In zone C (70% < WC < 90%), the clustered molecules are tightly packed, thus suppressing the molecular motion and vibration to enhance luminescence ( Figure 3 h(ii)). Very recently, the Li group also discovered the AIE phenomenon in Cu(I)-based cyclic trinuclear complexes (Cu(I)-CTC) [ 29 ]. These NCs exhibit no photoluminescence in pure tetrahydrofuran until water is added.…”

“…They showed that the key factors affecting the device performance were the concentration of metal NCs and the degree of zeolite anode contact. Last year, Li and coworkers introduced aggregation-enhanced Cu 3 (L 2 ) 3 (L 2 = 4-hexyl-3,5-dimethyl-1Hpyrazole) acting as an emissive layer into OLEDs [ 29 ], where the OLED exhibited red emission centering at 610 nm, with a current efficiency (of 7.21 cd/A), a luminance (1200 cd/m 2 ), as well as EQE (4%).…”

Multistimuli-responsive behavior of a phosphorescent Cu3pyrazolate3complex for luminescent logic gates and encrypted information transformation

“…35 Pyrazolate-based Cu(I) cyclic trinuclear complexes (CTCs) represent an important class in the family of coinage-metalbased CTCs, whose fascinating luminescence behaviors are often dominated by aggregation. 11,[36][37][38] Since 2003, 39 it has been well-documented that Cu(I) CTCs can show bright phosphorescence or changeable phosphorescence colours or intensities upon the formation of an excimer, exciplex, ground-state supramolecular polymer or adduct during aggregation. 11 The nine-membered Cu 3 N 6 coordination rings of Cu 3 pyrazolate 3 (Cu 3 Pz 3 ), providing Lewis acidic sites, π-acidic/basic sites, metal-metal interacting sites and low-lying intramolecular Cu⋯Cu excited states, often play an essential role in the abundant emissive properties, including photoluminescence (PL) thermochromism, mechanochromism, vapochromism, solvatochromism and concentration luminochromism.…”