ABSTRACT
The design and synthesis of highly luminescent organic molecules are key issues for various optoelectronic applications such as organic light-emitting diodes (OLEDs), organic light-emitting transistors, and organic lasers. Thermally activated delayed fluorescence (TADF) materials have attracted a great deal of attention as a new generation of emitter for OLEDs because they can overcome the limitation of theoretical maxima of ηext of 5%, without using expensive precious metals. This chapter focuses on the molecular design and optoelectronic properties of purely organic TADF materials for OLEDs. It describes some basic principles for TADF-OLEDs and demonstrates the molecular design concepts for efficient TADF materials. Reverse intersystem crossing and intersystem crossing are generally spin-forbidden transitions for most luminescent organic molecules. Organic luminescent materials generally display weakened emission when the molecules aggregate in their condensed solid states, compared to the molecularly isolated state. The chapter argues that the freedom for the TADF molecular design overcomes these problems in the near future.
