Near Infrared Phosphorescent Dinuclear Ir(III) Complex Exhibiting Unusually Slow Intersystem Crossing and Dual Emissive Behavior

Marsel Z Shafikov; Andrey V Zaytsev; Alfiya F Suleymanova; Fabian Brandl; Aleksandra Kowalczyk; Magdalena Gapińska; Konrad Kowalski; Valery N Kozhevnikov; Rafał Czerwieniec

doi:10.1021/acs.jpclett.0c01276

Near Infrared Phosphorescent Dinuclear Ir(III) Complex Exhibiting Unusually Slow Intersystem Crossing and Dual Emissive Behavior

J Phys Chem Lett. 2020 Aug 6;11(15):5849-5855. doi: 10.1021/acs.jpclett.0c01276. Epub 2020 Jul 10.

Authors

Marsel Z Shafikov^{1

2}, Andrey V Zaytsev³, Alfiya F Suleymanova⁴, Fabian Brandl¹, Aleksandra Kowalczyk⁵, Magdalena Gapińska⁶, Konrad Kowalski⁷, Valery N Kozhevnikov³, Rafał Czerwieniec¹

Affiliations

¹ Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitätsstrasse 31, Regensburg D-93053, Germany.
² Department for Technology of Organic Synthesis, Institute of Chemical Technology, Ural Federal University, Mira 19, Ekaterinburg 620002, Russia.
³ Department of Applied Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, U.K.
⁴ Department of Chemistry, University of York, Heslington, York YO10 5DD, U.K.
⁵ Department of Microbial Genetics, Faculty of Biology and Environmental Protection, University of Łódź, Banacha 12/16, 90-237 Łódź, Poland.
⁶ Laboratory of Microscopic Imaging and Specialized Biological Techniques, Faculty of Biology and Environmental Protection, University of Łódź, Banacha 12/16, 90-237 Łódź, Poland.
⁷ Department of Organic Chemistry, Faculty of Chemistry, University of Łódź, Tamka 12, 91-403 Łódź, Poland.

PMID: 32615767
DOI: 10.1021/acs.jpclett.0c01276

Abstract

A dinuclear iridium(III) complex IrIr shows dual emission consisting of near infrared (NIR) phosphorescence (λ_max = 714 nm, CH₂Cl₂, T = 300 K) and green fluorescence (λ_max = 537 nm). The NIR emission stems from a triplet state (T₁) localized on the ditopic bridging ligand (³LC). Because of the dinuclear molecular structure, the phosphorescence efficiency (Φ_PL = 3.5%) is high compared to those of other known red/NIR-emitting iridium complexes. The weak fluorescence stems from the lowest excited singlet state (S₁) of ¹LC character. The occurrence of fluorescence is ascribed to relatively slow intersystem crossing (ISC) from state S₁ (¹LC) to the triplet manifold. The measured ISC rate corresponds to a time constant τ_ISC of 2.1 ps, which is an order of magnitude longer than those usually found for iridium complexes. This slow ISC rate can be explained in terms of the LC character and large energy separation (0.57 eV) of the respective singlet and triplet excited states. IrIr is internalized by live HeLa cells as evidenced by confocal luminescence microscopy.