Molecular Road Map to Tuning Ground State Absorption and Excited State Dynamics of Long-Wavelength Absorbers
Molecular Road Map to Tuning Ground State Absorption and Excited State Dynamics of Long-Wavelength Absorbers
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DOI：
10.1021/jacs.7b09982
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发表时间：
2017-11-22
影响因子：
15
通讯作者：
Therien, Michael J.
中科院分区：
文献类型：
--
作者：
Bai, Yusong;Olivier, Jean-Hubert;Therien, Michael J.
实现同时具有大量近红外（NIR）吸收率和长寿命、高产率三重态激发态的发色团对于许多光电应用至关重要，例如光功率限制和三重态-三重态湮没光子上转换（TTA-UC）。然而，能隙定律确保这种发色团很少见，并且具有这种特性的吸收剂的分子工程已被证明具有挑战性。在这里，我们提出了一种通过利用乙炔桥联的（聚吡啶基）金属（II）（M；M = Ru，Os）-（porphinato）金属（II）（PM'；M' = Zn，Pt，Pd）分子结构（M-（PM'）（n）-M）来解决此设计问题的通用方法，其中高振荡器强度近红外吸收率高达850 nm，近乎统一的系间交叉(ISC) 量子产率 (Phi(ISC)) 和微秒时间尺度的三重激发态 (T-1) 寿命同时实现。通过改变重金属 d 轨道的原子系数对描述最初制备的单重态和三重态激发态波函数的单电子激发构型的贡献程度，我们 (i) 表明荧光 (k(F)(0))、S-1 -> S-0 非辐射衰变 (k(nr))、S-1 -> T-1 ISC (k(ISC)) 和 T-1 -> S-0 弛豫 (k(T1) 的相对幅度-> S0)) 速率常数可以在 M-(PM')(n)-M 化合物中进行微调，并且 (ii) 演示设计，其中 k(ISC) 大小主导单重态流形弛豫动力学，但不会引起 T-1 -> S-0 转换动力学，从而缩短微秒时间尺度的三重态寿命。值得注意的是，M-(PM')(n)-M 发色团的近红外光谱域吸收率远远超过了经典配位配合物和具有类似高三重态形成产率的有机材料的吸收率：与这些基准材料相比，这项工作表明这些 M-(PM')(n)-M 系统在极其适中的 S-1-T-1 能隙（类似于 0.25 eV）下实现了近单位 Phi(ISC)。这项研究强调了 M-(PM')(n)-M 平台的光物理多样性，并提出了一个新的长波长吸收体库，可以有效地填充长寿命的 T-1 态。
Realizing chromophores that simultaneously possess substantial near-infrared (NIR) absorptivity and long-lived, high-yield triplet excited states is vital for many optoelectronic applications, such as optical power limiting and triplet-triplet annihilation photon upconversion (TTA-UC). However, the energy gap law ensures such chromophores are rare, and molecular engineering of absorbers having such properties has proven challenging. Here, we present a versatile methodology to tackle this design issue by exploiting the ethyne-bridged (polypyridyl)metal(II) (M; M = Ru, Os)-(porphinato)metal(II) (PM'; M' = Zn, Pt, Pd) molecular architecture (M-(PM')(n)-M), wherein high-oscillator-strength NIR absorptivity up to 850 nm, near-unity intersystem crossing (ISC) quantum yields (Phi(ISC)), and triplet excited-state (T-1) lifetimes on the microseconds time scale are simultaneously realized. By varying the extent to which the atomic coefficients of heavy metal d orbitals contribute to the one-electron excitation configurations describing the initially prepared singlet and triplet excited-state wave functions, we (i) show that the relative magnitudes of fluorescence (k(F)(0)), S-1 -> S-0 nonradiative decay (k(nr)), S-1 -> T-1 ISC (k(ISC)), and T-1 -> S-0 relaxation (k(T1 -> S0)) rate constants can be finely tuned in M-(PM')(n)-M compounds and (ii) demonstrate designs in which the k(ISC) magnitude dominates singlet manifold relaxation dynamics but does not give rise to T-1 -> S-0 conversion dynamics that short-circuit a microseconds time scale triplet lifetime. Notably, the NIR spectral domain absorptivities of M-(PM')(n)-M chromophores far exceed those of classic coordination complexes and organic materials possessing similarly high yields of triplet-state formation: in contrast to these benchmark materials, this work demonstrates that these M-(PM')(n)-M systems realize near unit Phi(ISC) at extraordinarily modest S-1-T-1 energy gaps (similar to 0.25 eV). This study underscores the photophysical diversity of the M-(PM')(n)-M platform and presents a new library of long-wavelength absorbers that efficiently populate long-lived T-1 states.