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Phosphorescence quenching of neutral and cationic iridium(III) complexes by molecular oxygen and aromatic electron acceptors

Paper ID Volume ID Publish Year Pages File Format Full-Text
26063 43932 2016 11 PDF Available
Title
Phosphorescence quenching of neutral and cationic iridium(III) complexes by molecular oxygen and aromatic electron acceptors
Abstract

•Oxygen quenching of Ir(III) complexes proceeds via competing nonCT and CT channels.•Contribution of the CT channel can be predicted by ΔGel for electron transfer.•The rate constants of the non CT channels are evaluated by kinetic analyses.•The O2 quenching mechanism involving spin mixing in the CT complexes is revealed.

Phosphorescence quenching of neutral and cationic Ir(III) complexes by molecular oxygen and aromatic electron acceptors (AEAs) have been systematically investigated in acetonitrile. The phosphorescence quenching rate constant (kq) by AEAs increased with decreasing Gibbs energy change (ΔGel) of electron transfer and gave a diffusion-controlled rate constant (kd) of 2.0 × 1010 M−1s−1. The occurrence of electron transfer was substantiated by transient absorption measurements, although the separated ion yields were as low as 0.10–0.17. The oxygen quenching of the Ir(III) complexes originated mainly from two competing pathways through singlet and triplet encounter complexes: a noncharge-transfer (nCT) channel, which is regarded as internal conversion to produce singlet oxygen (1O2), and a charge-transfer (CT) channel, whose rate is governed by ΔGel. The kd value for the Ir(III) complex/O2 systems was estimated to be 4.1 × 1010 M−1s−1. For the systems with ΔGel ≲ −0.8 eV, the limiting kq value was 2.5 × 1010 M−1s−1 and the efficiencies (fΔ) of 1O2 production from triplet states quenched by oxygen were 0.40. The limiting kq value being greater than (4/9)kd and the fΔ value being larger than 0.25 suggested the involvement of 1O2 formation through intersystem crossing between singlet, triplet, and quintet CT complexes.

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Keywords
Iridium complex; Phosphorescence; Oxygen; Charge transfer; Electron transfer
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Phosphorescence quenching of neutral and cationic iridium(III) complexes by molecular oxygen and aromatic electron acceptors
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 324, 30 June 2016, Pages 134–144
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
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Don't Miss Today's Special Offer
Price was $35.95
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Price after discount Only $4.95
100% Money Back Guarantee
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