Issue 18, 2019

Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence

Abstract

The enantiomerically pure ligand P,P-diphenyl-N,N′-bis((R)-1-phenylethyl)phosphinimidic amide (1; (R)-HPEPIA) was synthesized and subsequently deprotonated with alkali metal precursors to yield dimeric complexes [M2{(R)-PEPIA}2] (M = Li (2), Na (3), K (4), Rb (5)). The cesium compound [M{(R)-PEPIA}] (6) crystallized as a cocrystal composed of dimeric ([Cs2{(R)-PEPIA}2] (6d) and 1D-polymeric ([Cs{(R)-PEPIA}]n) (6p) species in a 1 : 1 ratio. The coordination polymer 6p features a unique sinus-shaped configuration of repeating –Cs–N–P–N–Cs–N–P–N– units. Unusual photoluminescence (PL) properties were found for solid 1–6: in contrast to the fluorescent ligand 1, the alkali metal complexes show phosphorescence at low temperatures (<100 K) and thermally activated delayed fluorescence (TADF) above ∼150 K. The latter provides for PL quantum yields up to 36% (3) at ambient temperature. DFT calculations support that both 1 and 2–6d have similar singlet and triplet excited states with energy separations of a few tens of meV. The strongly enhanced intersystem crossing (ISC) in the metal complexes, resulting in TADF, is attributed to their dimeric structure. This suggests that the fluorophore dimerization may serve as a tool to effect ISC for the design of TADF emitters.

Graphical abstract: Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence

Supplementary files

Article information

Article type
Edge Article
Submitted
04 Feb 2019
Accepted
11 Mar 2019
First published
09 Apr 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2019,10, 4742-4749

Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence

T. J. Feuerstein, B. Goswami, P. Rauthe, R. Köppe, S. Lebedkin, M. M. Kappes and P. W. Roesky, Chem. Sci., 2019, 10, 4742 DOI: 10.1039/C9SC00629J

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