Photoluminescent Cu(I) HETPHENs Featuring Bulky Alkyl-Substituted Phenanthrolines

Successful excited-state-enhancing
substituent effect strategies
applied in homoleptic Cu(I) metal-to-ligand charge transfer (MLCT)
chromophores have been adapted to the heteroleptic phenanthroline
(HETPHEN) platform, leveraging 2,9-mesityl-1,10-phenanthroline (mesPhen)
in conjunction with a series of seven distinct 2,9- and 2,3,4,7,8,9-substituted
phenanthrolines. The newly conceived CuHETPHEN complexes feature MLCT
lifetimes ranging from 62 to 443 ns, all of which exhibit unprecedented
room-temperature photoluminescence and demonstrate quantitative adherence
to the energy gap law. TD-DFT calculations successfully modeled the
systematic variation in electronic transition intensities, accounting
for the experimentally observed UV–vis absorption bands across
the entire series of molecules while providing detailed structural
explanations for the variations in spectral profiles. These heteroleptic
Cu(I) diimine chromophores exhibit thermally activated delayed fluorescence
(TADF), with delayed fluorescence occurring between closely spaced 1MLCT and 3MLCT excited manifolds, having energetic
separations of ΔE = 713–1009 cm–1,
as demonstrated here for the first time. Nanosecond and ultrafast
transient absorption spectroscopy verified the MLCT nature of these
excited states and extracted the time constants for the initial pseudo-Jahn–Teller
distortion and intersystem crossing throughout the entire series of
molecules. Finally, the triplet photosensitization properties of these
Cu(I) HETPHENs are demonstrated in a number of model photochemical
transformations.

将高效的激发态增强取代基效应策略应用于全同配位Cu(I)金属-配体电荷转移（MLCT）发色团，现已适配至异配位菲咯啉（HETPHEN）平台，采用2,9-均三甲苯基-1,10-菲咯啉（mesPhen）与七种不同的2,9-及2,3,4,7,8,9-取代菲咯啉组合构建配合物。新设计的CuHETPHEN配合物的MLCT寿命介于62 ns至443 ns之间，所有配合物均展现出前所未有的室温光致发光特性，且严格遵循能隙定律。含时密度泛函理论（TD-DFT）计算成功模拟了电子跃迁强度的系统性变化，不仅重现了实验观测到的全系列分子的紫外-可见吸收峰，还为光谱轮廓的变化提供了精细的结构解释。这类异配位Cu(I)二亚胺发色团展现出热活化延迟荧光（TADF）特性，其延迟荧光发生在紧密相邻的1MLCT与3MLCT激发态流形之间，能级差ΔE为713–1009 cm⁻¹，此为首次报道。纳秒级与超快瞬态吸收光谱验证了这些激发态的MLCT属性，并提取了全系列分子中初始赝姜-泰勒畸变与系间窜越过程的时间常数。最后，本研究通过一系列模型光化学反应验证了这类Cu(I) HETPHEN配合物的三重态光敏化性能。