Molecular Design and Synthetic Pathways for Chiral/Achiral TADF and HLCT Emitters in Near Infrared Region: Recent Progress and Future Perspective

Abstract

The broad spectrum of applications of near-infrared (NIR) emitters ranging from organic light-emitting diodes (OLEDs) to advanced military technologies and in 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 discussion on the various mechanisms for achieving efficiencies beyond traditional fluorescence and the design strategies for developing TADF materials has been incorporated. 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 hold significant potential for multifunctional applications ranging from bioimaging to secure optical communication, have also 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.