[Cr(ddpd)2]3+: A Molecular, Water‐Soluble, Highly NIR‐Emissive Ruby Analogue. Issue 39 (12th August 2015)

• Record Type: Journal Article
• Authors: Otto, Sven; Grabolle, Markus; Förster, Christoph; Kreitner, Christoph; Resch‐Genger, Ute; Heinze, Katja
• Is Part Of: Angewandte Chemie international edition. Volume 54:Issue 39(2015)
• Page Start: 11572
• Page End: 11576
• Publication Date: 2015-08-12
• Subjects: chromium complexes -- intersystem crossing -- ligand‐field splitting -- NIR luminescence -- photophysics; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201504894
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Bright, long‐lived emission from first‐row transition‐metal complexes is very challenging to achieve. Herein, we present a new strategy relying on the rational tuning of energy levels. With the aid of the large N‐Cr‐N bite angle of the tridentate ligand ddpd ( N, N ′‐dimethyl‐ N, N ′‐dipyridine‐2‐ylpyridine‐2, 6‐diamine) and its strong σ‐donating capabilities, a very large ligand‐field splitting could be introduced in the chromium(III) complex [Cr(ddpd)2 ] 3+, that shifts the deactivating and photoreactive 4 T2 state well above the emitting 2 E state. Prevention of back‐intersystem crossing from the 2 E to the 4 T2 state enables exceptionally high near‐infrared phosphorescence quantum yields and lifetimes for this 3d metal complex. The complex [Cr(ddpd)2 ](BF4 )3 is highly water‐soluble and very stable towards thermal and photo‐induced substitution reactions and can be used for fluorescence intensity‐ and lifetime‐based oxygen sensing in the NIR. Abstract : Strong, long‐lived, and sharp NIR phosphorescence (775 nm, Φ =12 %, τ =899 μs) is achieved in the soluble chromium(III) complex [Cr(ddpd)2 ] 3+ (ddpd= N, N ′‐dimethyl‐ N, N ′‐dipyridin‐2‐ylpyridine‐2, 6‐diamine) by ligand‐field tuning through optimization of the ligand's bite angle and σ‐donor strength. 3 O2 quenches the emission, allowing for optical oxygen sensing. The highly stable complex is easy to prepare in high yields from inexpensive starting materials.