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

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-9H-carbazole-3,6-diamine (TTAC), and N 3 ,N 3 ,N 6 ,N 6 -tetrakis(4-methoxyphenyl)-9H-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.

Pyrazino[2,3-f][1,10]phenanthroline Derivatives as Robust Photocatalysts Enabling ppm-Level Organocatalyzed Photoinduced Electron/Energy Transfer Reversible Addition–Fragmentation Chain Transfer Polymerization

“…Compared to the 1 PC*, the 3 PC* exhibits a longer lifetime due to the prohibition of radiative transitions and the reduced rate of nonradiative transitions. , The strong distortion of the D–A molecular structure leads to a significant displacement of molecular orbitals between the donor and acceptor moieties, reducing the Δ E . This displacement and reduced overlap of molecular orbitals result in a smaller Δ E ST , thereby achieving a higher triplet quantum yield. − Pyzphen is used as the acceptor and TPA or phenyl-TPA is used as the electron donor to achieve a strongly distorted D–A structure (Figure d). The HOMO and LUMO electron distributions of PCs 5 and 6 with strong twisting structures are essentially separated, but there is a certain degree of electron cloud overlap on the pyridine ring of the pyzphen acceptor unit (Figure S8).…”

“…1,10-Phenanthroline and its derivatives, with their planar, rigid, and electron-deficient molecular skeletons, are widely employed in the molecular design of organic optoelectronic materials. − Recently, researchers have developed a novel series of red TADF materials featuring large conjugated planar and rigid acceptor structures based on the phenanthroline skeleton, aimed at suppressing nonradiative transitions and enhancing the luminescent efficiency of electroluminescent devices. − For instance, Xu et al successfully constructed red and deep-red TADF molecules with diverse configurations by utilizing dipyrido­[3,2- a :2,3- c ]­phenazine (DPPZ) as an electron acceptor and triphenylamine (TPA) as an electron donor. , Moreover, the Hudson group synthesized multiple novel luminescent TADF molecules with a donor (D)–acceptor (A) structure based on dibenzo­[ a,c ]­dipyrido­[3,2- h :20–30- j ]-phenazine-12-yl (BPPZ) as an acceptor, which have been successfully applied to bioimaging and cellular imaging. , These TADF molecules have shown great promise in advanced high-performance optoelectronic materials, as evidenced by their successful utilization in cutting-edge technological domains such as organic light-emitting diodes and bioimaging.…”

Controlling the Size of Glassy Organic Dots Exhibiting Thermally Activated Delayed Fluorescence for Bioimaging

“…Probes suitable for time-resolved imaging are highly sought after for biomedical applications, and utilizing long-lived emission from TADF can provide a metal-free route to temporal resolution. ,− Furthermore, probes emitting red or near-infrared light offer advantages in conventional fluorescence imaging because of improved tissue transparency, reduced background autofluorescence, and reduced light scattering in this spectral region. ,, Therefore, we chose to encapsulate the TADF emitter BPPZ-2TTAC within the Odots in this work. BPPZ-2TTAC has a long lifetime (139 μs) and orange-to-red emission (λ max = 583 nm) when doped in PMMA films, making it a suitable candidate for use in g-Odot optimization. When doped in g-Odots, the emission maximum red-shifted to 620 nm, thus putting a significant fraction of the emission well within the biological transparency window of 650–1350 nm.…”

Exploring the Versatile Uses of Triplet States: Working Principles, Limitations, and Recent Progress in Phosphorescence, TADF, and TTA

“…Apart from these typical TADF molecules, researchers have also extended these structures to design of TADF polymers and macromolecules (e.g., dendrimers), ,− aiming to improve the capability of solution-processing materials, potentially reduce processing cost, and enhance suitability for large-scale applications. − Among the examples, Hudson et al . designed a TADF dendimer based on the BPPZ acceptor substituted with dendritic donors, while Yang et al .…”