Molecularly Engineered Near-Infrared Light-Emitting Electrochemical Cells

The development of near-infrared (NIR) luminescent materials has emerged as a promising research field with important applications in solid-state lighting (SSL), night-vision-readable displays, and the telecommunication industry. Over the past two decades, remarkable advances in the development of light-emitting electrochemical cells (LECs) have stunned the SSL community, which has in turn driven the quest for new classes of stable, more efficient NIR emissive molecules. In this review, an overview of the state of the art in the field of near-infrared light-emitting electrochemical cells (NIR-LEC) is provided based on three families of emissive compounds developed over the past 25 years: i) transition metal complexes, ii) ionic polymers, and iii) host-guest materials. In this context, ionic and conductive emitters are particularly attractive since their emission can be tuned via molecular design, which involves varying the chemical nature and substitution pattern of their ancillary ligands. Herein, the challenges and current limitations of the latter approach are highlighted, particularly with respect to developing NIR-LECs with high external quantum efficiencies. Finally, useful guidelines for the discovery of new, efficient emitters for tailored NIR-LEC applications are presented, together with an outlook towards the design of new NIR-SSL materials.