Through-space interactions in thermally activated delayed fluorescent emitters : novel materials and organic light emitting diodes

Abstract

Thermally activated delayed fluorescence (TADF) has emerged as one of the most promising and efficient approaches realizing highly efficient organic light emitting diodes (OLEDs). This attractive approach utilizes organic emitters that can harvest all the excitons generated during the electroluminescent process to achieve 100% internal quantum efficiency. The TADF mechanism relies on the recruitment of triplet excitons, which occurs through their conversion to singlet excitons through a rapid reverse intersystem crossing (RISC) made possible by a very small singlet-triplet excited state energy difference (ΔE[sub](ST)). Since the first report of an efficient TADF OLED was published in 2012, the field has witnessed a tremendous development over the last 8 years. Many efforts have been devoted in developing an ideal TADF emitter with high photoluminescence quantum yield (Φ[sub](PL)), small ΔE[sub](ST), short delayed electroluminescence lifetime (τ[sub](d)) which should translate to OLEDs with high external quantum efficiencies (EQEs) and better efficiency roll offs. Various design strategies have been proposed, explored and adopted to optimize TADF materials for OLED applications. Throughout the course of this thesis, a design strategy based on “through-space” interactions has been extensively explored to optimize the material and device parameters in TADF. [2.2]Paracyclophane and spiro-conjugated scaffolds are introduced to the design pool of TADF materials and through the careful modulation of through-space interactions both theoretically and experimentally, the photo-physical properties are optimized, and state-of-the-art OLED performances are demonstrated.