Molecular design and synthetic pathways for chiral/achiral TADF and HLCT emitters in the near-infrared region: recent progress and future perspectives

Abstract

The broad spectrum of applications of near-infrared (NIR) emitters, ranging from organic light-emitting diodes (OLEDs) to advanced military technologies and bioimaging, is transforming the display industry. However, the energy gap law challenges the simultaneous achievement of high efficiency and narrow emissions, especially in the NIR region. Metal-free thermally activated delayed fluorescence (TADF) and hybridized local and charge transfer (HLCT) mechanisms open new pathways to achieve efficiencies beyond those of traditional fluorescence. However, NIR-TADF and HLCT materials still face challenges in attaining breakthrough efficiencies. Herein, brief discussions on the various mechanisms for achieving efficiencies beyond traditional fluorescence and design strategies for developing TADF materials are presented. Different synthetic approaches for developing NIR-TADF molecules have been discussed. In addition, recent advancements in NIR-TADF and HLCT materials, along with their photophysical properties and electroluminescence performance, have been emphasized. Moreover, the emerging class of chiral NIR-TADF materials, which holds significant potential for multifunctional applications ranging from bioimaging to secure optical communication, has been discussed. It is anticipated that this review article will serve as a valuable resource for the research community exploring molecular design strategies and synthetic approaches for the development of efficient NIR-TADF materials.