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Controlling the excited-state dynamics of low band gap near-infrared absorbers via proquinoidal unit electronic structural modulation

机译：通过proquinoidal单元电子结构调制控制低带隙近红外吸收体的激发态动力学

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While the influence of proquinoidal character upon the linear absorption spectrum of low optical bandgap π-conjugated polymers and molecules is well understood, its impact upon excited-state relaxation pathways and dynamics remains obscure. We report the syntheses, electronic structural properties, and excited-state dynamics of a series of model highly conjugated near-infrared (NIR)-absorbing chromophores based on a (porphinato)metal(ii)-proquinoidal spacer-(porphinato)metal(ii) (>PM-Sp-PM) structural motif. A combination of excited-state dynamical studies and time-dependent density functional theory calculations: (i) points to the cardinal role that excited-state configuration interaction (CI) plays in determining the magnitudes of S1 → S0 radiative (k r), S1 → T1 intersystem crossing (k ISC), and S1 → S0 internal conversion (k IC) rate constants in these >PM-Sp-PM chromophores, and (ii) suggests that a primary determinant of CI magnitude derives from the energetic alignment of the >PM and >Sp fragment LUMOs (ΔE L). These insights not only enable steering of excited-state relaxation dynamics of high oscillator strength NIR absorbers to realize either substantial fluorescence or long-lived triplets (τ T1 > μs) generated at unit quantum yield (Φ ISC = 100%), but also crafting of those having counter-intuitive properties: for example, while (porphinato)platinum compounds are well known to generate non-emissive triplet states (Φ ISC = 100%) upon optical excitation at ambient temperature, diminishing the extent of excited-state CI in these systems realizes long-wavelength absorbing heavy-metal fluorophores. This work highlights approaches to: (i) modulate low-lying singlet excited-state lifetime over the picosecond-to-nanosecond time domain, (ii) achieve NIR fluorescence with quantum yields up to 25%, (iii) tune the magnitude of S1–T1 ISC rate constant from 109 to 1012 s–1 and (iv) realize T1-state lifetimes that range from ∼0.1 to several μs, for these model >PM-Sp-PM chromophores, and renders new insights to evolve bespoke photophysical properties for low optical bandgap π-conjugated polymers and molecules based on proquinoidal conjugation motifs.
机译：尽管人们早已了解了原喹啉酮特性对低光学带隙π共轭聚合物和分子的线性吸收光谱的影响，但其对激发态弛豫途径和动力学的影响仍然不清楚。我们报告了基于（porphinato）metal（ii）-proquinoidal spacer-（porphinato）metal（ii）的一系列模型高度共轭的近红外（NIR）吸收发色团的合成，电子结构性质和激发态动力学）（> PM-Sp-PM ）结构图案。激发态动力学研究与时变密度泛函理论计算相结合：（i）指出激发态构型相互作用（CI）在确定S1→S0辐射（kr），S1→的大小中的主要作用这些> PM-Sp-PM 生色团中的T1系统间交叉（k ISC）和S1→S0内部转换（k IC）速率常数，并且（ii）建议CI量的主要决定因素来自> PM 和> Sp 片段LUMO（ΔEL）的能量比对。这些见解不仅可以控制高振荡器强度NIR吸收剂的激发态弛豫动力学，以实现以单位量子产率（ΦISC = 100％）产生的大量荧光或长寿命三重态（τT1>μs），而且还可以进行合成其中具有相反直觉特性的化合物：例如，众所周知，（卟啉）铂化合物在环境温度下进行光激发时会产生非发射三重态（ΦISC = 100％），从而降低了激发态CI的程度。这些系统实现了长波吸收重金属荧光团。这项工作重点介绍了以下方法：（i）在皮秒至纳秒时域内调制低态单线态激发态寿命；（ii）实现量子产率高达25％的NIR荧光；（iii）调整S1的幅度–T1 ISC速率常数从10 9 到10 12 s –1 ，并且（iv）实现T 1 -这些模型> PM-Sp-PM 发色团的状态寿命范围从〜0.1到几微秒，并为开发低光学带隙π共轭聚合物和基于原喹啉的分子的定制光物理性质提供了新见解。共轭图案。

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