Difluorodithieno[3,2-a:2′,3′-c]phenazine as a strong acceptor for materials displaying thermally activated delayed fluorescence or room temperature phosphorescence

A novel strong electron-acceptor unit, 9,10-difluorodithieno[3,2-a:2′,3′-c]phenazine (DTPz), is synthesized and applied in the design of two donor-acceptor type emitters displaying long-lived delayed emission. Using either 9,9-dimethyl-9,10-dihydroacridine (DMAC) or triisopropyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDT-TIPS) as the donor component, push-pull type chromophores exhibiting charge-transfer emission are obtained and found to afford either thermally activated delayed fluorescence (TADF) for DMAC or room temperature phosphorescence (RTP) for BDT-TIPS

Isomeric modulation of thermally activated delayed fluorescence in dibenzo[ a, c ]phenazine-based (deep) red emitters †

A series of four emissive regio-isomers are synthesized based on the dibenzo[a, c]phenazine-11,12-dicarbonitrile (DBPzCN) acceptor scaffold and a triphenylamine (TPA) donor. Density functional theory is utilized to compare the relative differences in molecular conformation, excited state distributions, and orbital interactions. Steady-state and time-resolved emission spectroscopy reveal strongly contrasting emissive properties and triplet harvesting of the four materials. In zeonex host emission maxima range widely, with differences of over 100 nm. Additionally, isomers 3-TPA-DBPzCN and 4-TPA-DBPzCN show photoluminescence quantum yields (PLQYs) of 46 and 62%, while 1-TPA-DBPzCN and 2-TPA-DBPzCN instead show values <1 and 24%, respectively. Relevant to thermally activated delayed fluorescence (TADF), very small singlet–triplet energy gaps are observed for isomers 2-TPA-DBPzCN and 4-TPA-DBPzCN, with corresponding reverse intersystem crossing (rISC) rates of 0.6 and 1.6 × 105 s−1, respectively. Unique in possessing both fast rISC and a relatively high PLQY, the unconventional 4-TPA-DBPzCN regio-isomer turns out to be an efficient TADF emitter, highlighting the important role of donor–acceptor substitution position in the design of efficient TADF materials targeting specific wavelength ranges