A stronger acceptor decreases the rates of charge transfer: ultrafast dynamics and on/off switching of charge separation in organometallic donor-bridge-acceptor systems.
A stronger acceptor decreases the rates of charge transfer: ultrafast dynamics and on/off switching of charge separation in organometallic donor-bridge-acceptor systems.
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DOI：
10.1039/d2sc06409j
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发表时间：
2023-10-25
期刊：
影响因子：
8.4
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中科院分区：
文献类型：
--
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为了揭示驱动力和结构变化在指导供体-桥-受体（DBA）系统中的光诱导途径中的作用，我们比较了新型DBA中的超快动力学，这些DBA共享吩噻嗪（PTZ）电子供体和Pt（ii）trans-acetylide桥（-CC-Pt-CC-），但具有不同的受体共轭到桥中（萘二酰亚胺，NDI;或萘单酰亚胺，NAP）。激发态动力学阐明瞬态吸收，时间分辨红外（TRIR，直接以下的电子密度变化的桥梁/受体），和宽带荧光上转换（FLUP，直接以下的亚皮秒系统间交叉）光谱，支持TDDFT计算。将强受体直接缀合到桥中导致最低激发态从配体内3 IL状态切换到所需的电荷分离的3CSS状态。我们观察到两个令人惊讶的影响，增加强度的受体在NDI与NAP：一个ca。70-3CSS形成的倍数减慢-（971 ps）−1vs。(14 ps）−1，3CSS的寿命更长（5.9 vs 1 ns）;这归因于驱动力ΔGet的差异和距离依赖性。100倍的增长率的系统间交叉-分-500 fs-由更强的受体突出了在这个过程中的重原子包含桥的离域的作用。几个激发态的紧密接近允许通过溶剂极性将3CSS的产率从100%控制到0%。新的DBA提供了一个多功能的平台，用于研究桥梁振动作为控制激发态动态的工具的作用。 系统间交叉的速率增加，而电荷分离和重组的速率下降，在供体-CC-Pt-CC-受体系统具有较强的电子受体-所揭示的荧光上转换和超快IR方法。
To unravel the role of driving force and structural changes in directing the photoinduced pathways in donor–bridge–acceptor (DBA) systems, we compared the ultrafast dynamics in novel DBAs which share a phenothiazine (PTZ) electron donor and a Pt(ii) trans-acetylide bridge (–CC–Pt–CC–), but bear different acceptors conjugated into the bridge (naphthalene-diimide, NDI; or naphthalene-monoimide, NAP). The excited state dynamics were elucidated by transient absorption, time-resolved infrared (TRIR, directly following electron density changes on the bridge/acceptor), and broadband fluorescence-upconversion (FLUP, directly following sub-picosecond intersystem crossing) spectroscopies, supported by TDDFT calculations. Direct conjugation of a strong acceptor into the bridge leads to switching of the lowest excited state from the intraligand 3IL state to the desired charge-separated 3CSS state. We observe two surprising effects of an increased strength of the acceptor in NDI vs. NAP: a ca. 70-fold slow-down of the 3CSS formation—(971 ps)−1vs. (14 ps)−1, and a longer lifetime of the 3CSS (5.9 vs. 1 ns); these are attributed to differences in the driving force ΔGet, and to distance dependence. The 100-fold increase in the rate of intersystem crossing—to sub-500 fs—by the stronger acceptor highlights the role of delocalisation across the heavy-atom containing bridge in this process. The close proximity of several excited states allows one to control the yield of 3CSS from ∼100% to 0% by solvent polarity. The new DBAs offer a versatile platform for investigating the role of bridge vibrations as a tool to control excited state dynamics. The rate of intersystem crossing increases, whilst the rates of charge separation and recombination decrease in donor–CC–Pt–CC–acceptor systems with a stronger electron acceptor – as revealed by fluorescence upconversion and ultrafast IR methods.
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