Naphthalimide-phenothiazine dyads: effect of conformational flexibility and matching of the energy of the charge-transfer state and the localized triplet excited state on the thermally activated delayed fluorescence.
Naphthalimide-phenothiazine dyads: effect of conformational flexibility and matching of the energy of the charge-transfer state and the localized triplet excited state on the thermally activated delayed fluorescence.
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DOI：
10.3762/bjoc.18.149
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发表时间：
2022
影响因子：
2.7
通讯作者：
Jacquemin D
中科院分区：
文献类型：
--
作者：
Ye K;Cao L;van Raamsdonk DME;Wang Z;Zhao J;Escudero D;Jacquemin D
为了研究电子供体-受体分子中构象灵活性以及电荷转移（CT）和局域三重激发（3LE）态能量匹配对热激活延迟荧光（TADF）的共同影响，制备了一系列紧凑的电子供体-受体二元组和三元组，以萘二甲酰亚胺（NI）为电子受体，吩噻嗪（PTZ）为电子供体。 NI和PTZ部分或者通过C-N单键直接连接在NI的3位和PTZ部分的N位，或者通过苯基连接。 CT和LE态能级的调节是通过将PTZ单元氧化成相应的亚砜来实现的，而构象限制是通过在苯基连接基上引入邻甲基取代基来实现的，从而可以控制CT和3LE态之间的耦合强度。 NI-PTZ 在正己烷中的单线态氧量子产率 (ΦΔ) 适中 (HEX, ΦΔ = 19%)。观察到二元组的 TADF，二元组的双指数发光寿命为 16.0 ns (99.9%)/14.4 μs (0.1%)，三元组的双指数发光寿命为 7.2 ns (99.6%)/2.0 μs (0.4%)。在纳秒瞬态吸收光谱中观察到三重态，其寿命在 4-48 μs 范围内。计算研究表明，正交电子供体-受体分子结构有利于 TADF。这些计算表明3LE和3CT状态之间的能量差异很小，这有助于解释ns-TA光谱和NI-PTZ中TADF的起源，这最终是由于3LE和3CT状态之间的能量差异很小。相反，NI-PTZ-O 具有更高的 CT 状态并具有更稳定的 3LE 状态，不显示 TADF。
In order to investigate the joint influence of the conformation flexibility and the matching of the energies of the charge-transfer (CT) and the localized triplet excited (3LE) states on the thermally activated delayed fluorescence (TADF) in electron donor–acceptor molecules, a series of compact electron donor–acceptor dyads and a triad were prepared, with naphthalimide (NI) as electron acceptor and phenothiazine (PTZ) as electron donor. The NI and PTZ moieties are either directly connected at the 3-position of NI and the N-position of the PTZ moiety via a C–N single bond, or they are linked through a phenyl group. The tuning of the energy order of the CT and LE states is achieved by oxidation of the PTZ unit into the corresponding sulfoxide, whereas conformation restriction is imposed by introducing ortho-methyl substituents on the phenyl linker, so that the coupling magnitude between the CT and the 3LE states can be controlled. The singlet oxygen quantum yield (ΦΔ) of NI-PTZ is moderate in n-hexane (HEX, ΦΔ = 19%). TADF was observed for the dyads, the biexponential luminescence lifetime are 16.0 ns (99.9%)/14.4 μs (0.1%) for the dyad and 7.2 ns (99.6%)/2.0 μs (0.4%) for the triad. Triplet state was observed in the nanosecond transient absorption spectra with lifetimes in the 4–48 μs range. Computational investigations show that the orthogonal electron donor–acceptor molecular structure is beneficial for TADF. These calculations indicate small energetic difference between the 3LE and 3CT states, which are helpful for interpreting the ns-TA spectra and the origins of TADF in NI-PTZ, which is ultimately due to the small energetic difference between the 3LE and 3CT states. Conversely, NI-PTZ-O, which has a higher CT state and bears a much more stabilized 3LE state, does not show TADF.
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