Thermally Activated Delayed Fluorescence Behavior Investigation in the Different Polarity Acceptor and Donor Molecules

To investigate the influence of intramolecular charge transfer (CT) characteristics, rigidity, and polarity of a molecule on photophysical properties, we designed and synthesized two types of thermally activated delayed fluorescence (TADF) emitters with malononitrile and acrylonitrile moieties as electron accepting units. Their photophysical properties such as singlet–triplet energy split (ΔE ST), photoluminescence quantum yields (PLQYs), and electronic structures were theoretically and experimentally evaluated. Among the synthesized materials, the emitters with an acrylonitrile moiety as an acceptor and phenoxazine, dimethylacridine, and tert-butylcarbazole as a donor revealed small ΔE ST values, good PLQYs, and efficient TADF performances. In contrast, the malononitrile derivatives demonstrated high ΔE ST values, very low PLQYs, and relatively poor TADF performances even though they have strong intramolecular CT characteristics and high polarity. We found that high molecular polarity and strong intramolecular CT characteristics are not essential factors for attaining good TADF performances over molecular rigidity.