The article provides a comprehensive review of thermally activated delayed fluorescence (TADF) materials, focusing on their optoelectronic behavior and performance in organic light-emitting diodes (OLEDs). TADF materials, which can be purely organic, offer a paradigm shift by replacing phosphorescent metal complexes with inexpensive organic compounds in electroluminescent devices, potentially enabling low-cost lighting and displays. The review compares TADF emitters across specific color ranges, including blue, green-yellow, orange-red, and white OLEDs, and discusses their use as host materials. It highlights the importance of the structure-optoelectronic property correlations in TADF materials and their role in achieving high external quantum efficiency (EQE) in OLEDs. The success of TADF materials has led to the development of the next generation of OLEDs, with device EQEs exceeding 30%. The article also delves into the design principles of TADF emitters, emphasizing the role of small singlet-triplet energy gaps and the importance of efficient reverse intersystem crossing (RISC) processes.The article provides a comprehensive review of thermally activated delayed fluorescence (TADF) materials, focusing on their optoelectronic behavior and performance in organic light-emitting diodes (OLEDs). TADF materials, which can be purely organic, offer a paradigm shift by replacing phosphorescent metal complexes with inexpensive organic compounds in electroluminescent devices, potentially enabling low-cost lighting and displays. The review compares TADF emitters across specific color ranges, including blue, green-yellow, orange-red, and white OLEDs, and discusses their use as host materials. It highlights the importance of the structure-optoelectronic property correlations in TADF materials and their role in achieving high external quantum efficiency (EQE) in OLEDs. The success of TADF materials has led to the development of the next generation of OLEDs, with device EQEs exceeding 30%. The article also delves into the design principles of TADF emitters, emphasizing the role of small singlet-triplet energy gaps and the importance of efficient reverse intersystem crossing (RISC) processes.