Compact electron donor–acceptor triads based on carbazole (Cz) and naphthalenediimide (NDI) were prepared to study the spin–orbit charge-transfer intersystem crossing (SOCT-ISC). By variation of the molecular conformation and electron-donating ability of the carbazole moieties, the electronic coupling between the two units was tuned, and as a result charge-transfer (CT) absorption bands with different magnitudes were observed (ε = 4000–18 000 M^–1 cm^–1). Interestingly, the triads with NDI attached at the 3-C position or with a phenyl spacer at the N position of the Cz moiety, thermally activated delayed fluorescence (TADF) was observed. Femtosecond transient absorption (fs-TA) spectroscopy indicated fast electron transfer (0.8–1.5 ps) from the Cz to NDI unit, followed by population of the triplet state (150–600 ps). Long-lived triplet states (up to τ_T = 45–50 μs) were observed for the triads. The solvent-polarity-dependent singlet-oxygen quantum yield (Φ_Δ) is 0–26%. Time-resolved electron paramagnetic resonance (TREPR) spectral study of TADF molecules indicated the presence of the ³CT state for NDI-Cz-Ph (zero-field-splitting parameter D = 21 G) and an ³LE state for NDI-Ph-Cz (D = 586 G). The triads were used as triplet photosensitizers in triplet–triplet annihilation upconversion by excitation into the CT absorption band; the upconversion quantum yield was Φ_UC = 8.2%, and there was a large anti-Stokes shift of 0.55 eV. Spatially confined photoexcitation is achieved with the upconversion using focusing laser beam excitation, and not the normally used collimated laser beam, i.e., the upconversion was only observed at the focal point of the laser beam. Photo-driven intermolecular electron transfer was demonstrated with reversible formation of the NDI^–• radical anion in the presence of the sacrificial electron donor triethanolamine.

中文翻译：

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紧凑型萘二亚胺-咔唑电子-供体-受体三元组的自旋-轨道电荷-转移系统间交叉

制备了基于咔唑 (Cz) 和萘二亚胺 (NDI) 的紧凑电子供体-受体三元组来研究自旋轨道电荷转移系统间交叉 (SOCT-ISC)。通过咔唑部分的分子构象和给电子能力的变化，调整了两个单元之间的电子耦合，结果观察到了不同幅度的电荷转移 (CT) 吸收带 (ε = 4000–18 000米^–1厘米^–1 )。有趣的是，在 3-C 位置带有 NDI 或在N带有苯基间隔基的三联体Cz 部分的位置，观察到热激活延迟荧光 (TADF)。飞秒瞬态吸收 (fs-TA) 光谱表明从 Cz 到 NDI 单元的快速电子转移 (0.8-1.5 ps)，然后是三重态 (150-600 ps)。观察到三重态的长寿命三重态（高达 τ _T = 45-50 μs）。溶剂极性相关的单线态氧量子产率 (Φ _Δ ) 为 0–26%。TADF 分子的时间分辨电子顺磁共振 (TREPR) 光谱研究表明存在NDI-Cz-Ph的³ CT 状态（零场分裂参数D = 21 G）和NDI-Ph-的³ LE 状态Cz ( D= 586 克）。三重态被用作三重态-三重态湮灭上转换中的三重态光敏剂，通过激发进入 CT 吸收带；上转换量子产率为 Φ _UC = 8.2%，反斯托克斯位移为 0.55 eV。空间受限的光激发是通过使用聚焦激光束激发的上转换实现的，而不是通常使用的准直激光束，即仅在激光束的焦点处观察到上转换。在牺牲电子供体三乙醇胺的存在下，NDI ^–•自由基阴离子的可逆形成证明了光驱动的分子间电子转移。