Dibenzodipyridophenazines with Dendritic Electron Donors Exhibiting Deep-Red Emission and Thermally Activated Delayed Fluorescence.

The development of deep-red thermally activated delayed fluorescence (TADF) emitters is important for applications such as organic light-emitting diodes (OLEDs) and biological imaging. Design strategies for red-shifting emission include synthesizing rigid acceptor cores to limit nonradiative decay and employing strong electron-donating groups. In this work, three novel luminescent donor-acceptor compounds based on the dibenzo[ a , c ]dipyrido[3,2-h:20-30- j ]-phenazine-12-yl ( BPPZ ) acceptor were prepared using dendritic carbazole-based donors 3,3″,6,6″-tetramethoxy-9' H -9,3':6',9″-tercarbazole ( TMTC ), N 3 , N 3 , N 6 , N 6 -tetra- p -tolyl-9 H -carbazole-3,6-diamine ( TTAC ), and N 3 , N 3 , N 6 , N 6 -tetrakis(4-methoxyphenyl)-9 H -carbazole-3,6-diamine ( TMAC ). Here, dimethoxycarbazole, ditolylamine, and bis(4-methoxyphenyl)amine were introduced at the 3,6-positions of carbazole to increase the strength of these donors and induce long-wavelength emission. Substituent effects were investigated with experiments and theoretical calculations. The emission maxima of these materials in toluene were found to be 562, 658, and 680 nm for BPPZ-2TMTC , BPPZ-2TTAC , and BPPZ-2TMAC , respectively, highlighting the exceptional strength of the TMAC donor, which pushes the emission into the deep-red region of the visible spectrum as well as into the biological transparency window (650-1350 nm). Long-lived emission lifetimes were observed in each emitter due to TADF in BPPZ-2TMC and BPPZ-2TTAC , as well as room-temperature phosphorescence in BPPZ-2TMAC . Overall, this work showcases deep-red emissive dendritic donor-acceptor materials which have potential as bioimaging agents with emission in the biological transparency window.