Dibenzodipyridophenazines with Dendritic Electron Donors Exhibiting Deep-Red Emission and Thermally Activated Delayed Fluorescence
William L. Primrose, Don M. Mayder, Ryoga Hojo, Zachary M. Hudson
Abstract
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.