Molecular ruby: exploring the excited state landscape

The discovery of the highly NIR-luminescent molecular ruby [Cr(ddpd) 2 ] 3+ (ddpd = N , N ′-dimethyl- N , N ′-dipyridin-2-ylpyridine-2,6-diamine) has been a milestone in the development of earth-abundant luminophors and has led to important new impulses in the field of spin-flip emitters. Its favourable optical properties such as a high photoluminescence quantum yield and long excited state lifetime are traced back to a remarkable excited state landscape which has been investigated in great detail. This article summarises the results of these studies with the aim to create a coherent picture of the excited state ordering and the ultrafast as well as long-timescale dynamics. Additional experimental data is provided to fill in gaps left by previous reports. Gorgeous view: we describe our current understanding of the rich excited state landscape of the highly luminescent molecular ruby. Experimental and theoretical results are put into perspective to uncover the secrets of this intriguing luminophore.