Understanding and exploiting long-lived near-infrared emission of a molecular ruby

Abstract

Enabling strong and long-lived NIR emission from complexes with earth-abundant metal ions is exemplified by embedding chromium(III) in a very strong ligand field yielding the molecular ruby [Cr(ddpd) 2 ] 3+ . This review aims at illustrating the main non-radiative decay pathways for electronically excited chromium(III) complexes, namely back-intersystem crossing, excited state distortion and multiphonon relaxation and at controlling these pathways by molecular design. The case study of [Cr(ddpd) 2 ] 3+ highlights recent successful design strategies and discusses first applications of the highly emissive 3d metal complex as optical sensor molecule and as photosensitizer.