Thermally Activated Delayed Fluorescence Pendant Copolymers with Electron- and Hole-Transporting Spacers.

To study the effect of hole- and electron-transporting spacers in copolymers on the thermally activated delayed fluorescence (TADF) properties and device efficiency of copolymers, two series of copolymers PCzPT-x and POPT-x have been designed and synthesized successfully. In these copolymers, 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide units give green-yellow TADF, while hole-transporting 9-(4-vinylphenyl)-9H-carbazole units or electron-transporting diphenyl(4-vinylphenyl)phosphine oxide act as spacers or hosts. Their thermal, electrochemical, photophysical, and electroluminescent properties and theoretical calculations are systematically investigated to illustrate the relationships between molecular structures and photophysical properties. By optimizing the upconversion and radiative decay rate and managing the energy transfer, a green-yellow device based on POPT-25 achieves a maximum external quantum efficiency of 5.2%, a current efficiency of 16.8 cd/A, and a power efficiency of 7.8 lm/W with CIE coordinates of (0.36, 0.50). Moreover, an external quantum efficiency of 3.5% at the practical luminescence of 100 cd/m is obtained.