The design of thermally activated delayed fluorescence (TADF) materials both as emitters and as hosts is an exploding area of research. The replacement of phosphorescent metal complexes with inexpensive organic compounds in electroluminescent (EL) devices that demonstrate comparable performance metrics is paradigm shifting, as these new materials offer the possibility of developing low‐cost lighting and displays. Here, a comprehensive review of TADF materials is presented, with a focus on linking their optoelectronic behavior with the performance of the organic light‐emitting diode (OLED) and related EL devices. TADF emitters are cross‐compared within specific color ranges, with a focus on blue, green–yellow, orange–red, and white OLEDs. Organic small‐molecule, dendrimer, polymer, and exciplex emitters are all discussed within this review, as is their use as host materials. Correlations are provided between the structure of the TADF materials and their optoelectronic properties. The success of TADF materials has ushered in the next generation of OLEDs.

Two novel charged organic thermally activated delayed fluorescence (TADF) emitters, 1 and 2, have been synthesized. Their TADF behavior is well-supported by the multiexponential decay of their emission (nanosecond and microsecond components) and the oxygen dependence of the photoluminescence quantum yields. Spin-coated electroluminescent devices have been fabricated to make light-emitting electrochemical cells (LEECs) and organic light-emitting diodes (OLEDs). The first example of a non-doped charged small organic molecule LEEC is reported and exhibited an external quantum efficiency (EQE) of 0.39% using 2. With a multilayer architecture, a solution-processed OLED device using neat 2 as the emitting layer gave an EQE of 5.1%, the highest reported to date for a nondoped solution-processed small molecule organic TADF OLED. These promising results open up a new area in light-emitting materials for the development of low-cost TADF LEECs.

Two deep blue thermally activated delayed fluorescence (TADF) emitters (imCzDPS and imDPADPS) that contain charged imidazolium groups tethered to the central luminophore were designed and synthesized as small molecule organic emitters for light-emitting electrochemical cell (LEEC) electroluminescent devices. The emission profile of the doped thin films (5 wt% in PMMA) is very blue and narrow (λ_PL: 414 nm and 409 nm; full width at half maximum (FHWM): 62 nm and 46 nm for imCzDPS and imDPADPS, respectively) with good photoluminescence quantum efficiencies (Φ_PL: 44% and 49% for imCzDPS and imDPADPS, respectively). In neat films, emission maxima occur at 440 nm and 428 nm for imCzDPS and imDPADPS, respectively, with comparable Φ_PL values of 44 and 61%, respectively. Both emitters exhibit biexponential emission decay kinetics (nanosecond prompt and microsecond delayed fluorescence) in both MeCN solution and thin films, characteristic of TADF behaviour. While imDPADPS did not show any emission in the LEEC device, that of imCzDPS gave an electroluminescence (EL) maximum at 470 nm and CIE coordinates of (0.208, 0.250), which makes this device amongst the bluest reported to date. However, the maximum device luminance achieved was 2.5 cd m⁻² and this poor brightness was attributed to the electrochemical instability of the emitter in the LEEC architecture, as evidenced by the additional peak at around 550 nm observed in the EL spectrum.

Polymer organic light-emitting diodes (PLED) are one of the most studied subjects in flexible electronics thanks to their economical wet fabrication procedure for enhanced price advantage of the product device. In order to optimize PLED efficiency, correlating the polymer structure with the device performance is essential. An important question for the researchers in this field is whether the polymer backbone is conjugated or not as it affects the device performance. In this review, recent advances in non-conjugated polymers employed as the emitting layer in PLED devices are first discussed, followed by their contrast with the conjugated counterparts in terms of polymer synthesis, sample quality, physical properties and device performances. Such comparison between conjugated and non-conjugated polymers for PLED applications is rarely attempted, and; hence, this review shall provide a useful insight of emitting polymers employed in PLEDs.

In this study, a series of four formyl-substituted chloro-bridged iridium(III) dimers were prepared. Their absorption, photophysical and electrochemical properties were studied in dichloromethane solution. It was found that as the formyl content increased on the cyclometalating ligands, emission unexpectedly became brighter. Organic light-emitting diodes (OLEDs) were fabricated using each of these iridium dimers as the emitter. The OLED fabricated using the brightest of the series, 2b, as the dopant afforded a decent external quantum efficiency (EQE) of 2.6%. This suggests that chloro-bridged iridium dimers are potential candidates as solid-state emitters.