Indirect Control of Donor/Acceptor Interactions for Highly Efficient Space-Confined Thermally Activated Delayed Fluorescence Emitters

摘要

Conformational engineering is essential to further reinforce the luminescentproperties of thermally activated delayed fluorescence (TADF) materialsfeaturing through-space charge transfer (TSCT) characteristics. Herein, twoTSCT-TADF emitters (8MeDM-B and 8FDM-B) with the methyl and fluorinemoieties substituted at the C8 site of the rigid spiro-fluorene bridge isreported. Derivation of the C8 site is first proposed to control the molecularconfiguration with the ability to indirectly tune the intramolecular interactionbetween donor and acceptor groups. As a result, 8MeDM-B and 8FDM-Bboth present small singlet-triplet energy gaps, fast reverse intersystemcrossing rates, and high photoluminescence quantum yields. Interestingly,the smaller fluorine atom not the bigger methyl group exhibits more evidentelectrostatic repulsive force onto the central donor and thus rectifies the centralspiro structure. Consequently, the high external quantum efficiency valuesof 28.8 and 31.7 for 8MeDM-B and 8FDM-B-based electroluminescencedevices are achieved, respectively. This study offers a measure for enhancingTSCT-TADF emitters without directly modifying the donor or acceptor.