Spiro donor-acceptor TADF emitters: naked TADF free from inhomogeneity caused by donor acceptor bridge bond disorder. Fast rISC and invariant photophysics in solid state hosts
Spiro donor-acceptor TADF emitters: naked TADF free from inhomogeneity caused by donor acceptor bridge bond disorder. Fast rISC and invariant photophysics in solid state hosts
复制标题
DOI：
10.1039/d1tc04484b
复制
发表时间：
2022-01-04
影响因子：
6.4
通讯作者：
Monkman, Andrew
中科院分区：
文献类型：
--
作者：
Franca, Larissa Gomes;Danos, Andrew;Monkman, Andrew
我们研究了螺桥给体-受体分子10-苯基-10H，10 'H-螺[吖啶-9，9-蒽]-10 '-酮（ACRSA）在主客体薄膜中的热激活延迟荧光（TADF）性质，并以其为探针探讨了典型OLED主体材料中主体效应对TADF机制的影响。通过刚性螺环C-C键而不是柔性C-N键连接，我们没有观察到供体-受体桥二面角分布引起的不均匀效应。ACRSA不显示提示或延迟电荷转移（CT）发射的时间依赖性“表观”红移。此外，使用一系列不同的主机，我们表明，基态偶极矩（介电值）的主机上的ACRSA CT能量的影响很小，即没有所谓的“固态solvatochromism”。这导致所有主体中CT状态的弱稳定性，但在膜中具有非常小的单线态三重态间隙和非常快且有效的单指数rISC速率（在zeonex主体中达到近10（7）s（-1））。我们没有观察到幂律衰减的DF尾，因为施主和受主单元之间没有二面角的色散。先前报道的ACRSA中低得多的rISC率被重新归因于分子间激基缔合物状态。分子间的物种引起额外的缓慢TADF的贡献，并扩大整体CT发射带在10%ACRSA加载和整洁的电影。利用由分离的ACRSA分子显示的快速和均匀的rISC可以在未来的TADF OLED中解锁更高的效率和关键的延长的操作寿命。
We have studied the thermally activated delayed fluorescence (TADF) properties of the spiro-bridged donor-acceptor molecule, 10-phenyl-10H,10 ' H-spiro[acridine-9,9-anthracen]-10 '-one, (ACRSA) in guest-host films and used it as a probe to explore the details of host effects on the TADF mechanism in typical OLED host materials. Linked by the rigid spiro C-C bond rather than a flexible C-N bond, we observe no inhomogeneous effects arising from distributions of donor-acceptor bridge dihedral angles. ACRSA displays no time dependent 'apparent' red shift of the prompt or delayed charge transfer (CT) emission. Moreover, using a range of different hosts, we show that the ground state dipole moment (dielectric value) of the host has very little effect on the ACRSA CT energy, i.e. there is no so-called 'solid state solvatochromism'. This leads to weak stabilisation of the CT state in all hosts, but has a very small singlet triplet gap and very fast and efficient monoexponential rISC rates in films (reaching nearly 10(7) s(-1) in zeonex host). We observe no power law decaying DF tail because there is no dispersion of the dihedral angle between donor and acceptor units. The previously much lower reported rISC rates in ACRSA are instead reattributed to intermolecular excimer states. The intermolecular species give rise to additional slow TADF contributions and broaden the overall CT emission band at 10% ACRSA loading and in neat films. Harnessing the rapid and homogenous rISC displayed by isolated ACRSA molecules may unlock higher efficiencies and - crucially - extended operational lifetimes in future TADF OLEDs.