Ward Jonathan S, Kukhta Nadzeya A, Dos Santos Paloma L, Congrave Daniel G, Batsanov Andrei S, Monkman Andrew P, Bryce Martin R
Department of Chemistry, Durham University, Durham DH1 3LE, U.K.
Department of Physics, Durham University, Durham DH1 3LE, U.K.
Chem Mater. 2019 Sep 10;31(17):6684-6695. doi: 10.1021/acs.chemmater.9b01184. Epub 2019 May 22.
We report the synthesis and structural and photophysical characterization of two series of molecules with functionalized azatriangulene electron donor cores and three pendant electron acceptor units. The presented donor and acceptor units are joined by C-C bonds, instead of the usual C-heteroatom bonds often found in thermally activated delayed fluorescence (TADF) emitters. The effects of the donor-acceptor strength and donor-acceptor dihedral angle on the emission properties are assessed. The data establish that the singlet-triplet energy gap is >0.3 eV and that delayed emission is present in only specific host matrices, irrespective of host polarity. Specific host behavior is atypical of many TADF materials, and we suggest the delayed emission in this work does not occur by a conventional vibronically coupled TADF mechanism, as the Δ value is too large. Detailed photophysical analysis and supporting density functional theory calculations suggest that some presented azatriangulene molecules emit via an upper-triplet state crossing mechanism. This work highlights that several different mechanisms can be responsible for delayed emission, often with highly similar photophysics. Detailed photophysical analysis is required to establish which delayed emission mechanism is occurring. Our results also highlight a clear future direction toward vibronically coupled C-C bonded TADF materials.
我们报道了具有功能化氮杂三角烯电子供体核心和三个侧基电子受体单元的两个系列分子的合成、结构及光物理表征。所呈现的供体和受体单元通过C-C键相连，而非热活化延迟荧光（TADF）发光体中常见的C-杂原子键。评估了供体-受体强度和供体-受体二面角对发射性质的影响。数据表明，单线态-三线态能隙大于0.3 eV，且仅在特定主体基质中存在延迟发射，与主体极性无关。特定主体行为在许多TADF材料中并不典型，我们认为本工作中的延迟发射并非通过传统的振动耦合TADF机制发生，因为Δ值过大。详细的光物理分析及支持性的密度泛函理论计算表明，一些所呈现的氮杂三角烯分子通过上三线态交叉机制发射。这项工作强调，几种不同的机制可能导致延迟发射，其光物理性质往往高度相似。需要进行详细的光物理分析以确定发生了哪种延迟发射机制。我们的结果还突出了振动耦合C-C键合TADF材料未来明确的发展方向。
