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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Effects of Structural Deformations on Optical Properties of Tetrabenzoporphyrins:Free-Bases and Pd Complexes
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Effects of Structural Deformations on Optical Properties of Tetrabenzoporphyrins:Free-Bases and Pd Complexes

机译：结构变形对四苯并卟啉：游离碱和Pd配合物光学性质的影响

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摘要

A recently developed method of synthesis of π-extended porphyrins made it possible to prepare a series of tetrabenzoporphyrins (TBP) with different numbers of meso-aryl substituents. The photophysical parameters of free-bases and Pd complexes of meso-unsubstituted TBP's, 5,15-diaryl-TBP's (Ar2TBP's) and 5,10,15,20-tetraaryl-TBP's (Ar4TBP's) were measured. For comparison, similarly meso-arylsubstituted porphyrins fused with nonaromatic cyclohexeno-rings, i.e. Ar_n-tetracyclohexenoporphyrins (Ar_nTCHP's, n = 0, 2, 4), were also synthesized and studied. Structural information was obtained by ab initio (DFT) calculations and X-ray crystallography. It was found that: 1) Free-base Ar4TBP's are strongly distorted out-of-plane (saddled), possess broadened, red-shifted spectra, short excited-state lifetimes and low fluorescence quantum yields (τ_(fl) = 2—3 ns, φ_(fl) = 0.02—0.03). These features are characteristic of other nonplanar free-base porphyrins, including Ar4TCHP's. 2) Ar2TBP free-bases possess completely planar geometries, although with significant in-plane deformations. These deformations have practically no effect on the singlet excited-state properties of Ar2TBP's as compared to planar meso-unsubstituted TBP's. Both types of porphyrins retain strong fluorescence (τ_(fl) = 10—12 ns, φ_(fl) = 0.3—0.4), and their radiative rate constants (k_r) are 3—4 times higher than those of planar H2TCHP's. 3) Nonplanar deformations dramatically enhance nonradiative decay of triplet states of regular Pd porphyrins. For example, planar PdTCHP phosphoresces with high quantum yield (φ_(phos) = 0.45, τ_(phos) = 1118 μs), while saddled PdPh4TCHP is practically nonemissive. In contrast, both raffled and saddled PdAr_nTBP's retain strong phosphorescence at ambient temperatures (PdPh2TBP: τ_(phos) = 496 μs, φ_(phos)=0.15; PdPh4TBP: τ_(phos) = 258 μs, φ_(phos) = 0.08). It appears that π-extension is capable of counterbalancing deleterious effects of nonplanar deformations on triplet emissivity of Pd porphyrins.
机译：最近开发的合成π-延伸的卟啉的方法使得制备一系列具有不同数量的内-芳基取代基的四苯并卟啉（TBP）成为可能。测量了内消旋取代的TBP，5,15-二芳基-TBP（Ar2TBP）和5,10,15,20-四芳基-TBP（Ar4TBP）的游离碱和Pd配合物的光物理参数。为了进行比较，还合成并研究了类似的与非芳族环己烯环稠合的内-芳基取代的卟啉，即Ar_n-四环己烯卟啉（Ar_nTCHP，n ＝ 0、2、4）。结构信息是通过从头算（DFT）计算和X射线晶体学获得的。发现：1）游离碱Ar4TBP严重偏离平面（马鞍形），具有加宽的红移光谱，激发态寿命短和低荧光量子产率（τ_（fl）= 2-3 ns，φ_（fl）= 0.02-0.03）。这些特征是包括Ar4TCHP在内的其他非平面游离碱卟啉的特征。 2）Ar2TBP游离碱具有完全平面的几何形状，尽管具有显着的面内变形。与平面内未取代的TBP相比，这些变形对Ar2TBP的单重激发态性质几乎没有影响。两种卟啉均保留强荧光（τ_（fl）= 10-12 ns，φ_（fl）= 0.3-0.4），并且它们的辐射速率常数（k_r）是平面H2TCHP辐射速率常数的3-4倍。 3）非平面形变显着增强了规则Pd卟啉三重态的非辐射衰减。例如，平面PdTCHP以高量子产率（φ_（phos）= 0.45，τ_（phos）= 1118μs）发出磷光，而背负的PdPh4TCHP实际上是无用的。相比之下，在环境温度下，摇晃的PdAr_nTBP和马鞍形的PdAr_nTBP都保留了强烈的磷光（PdPh2TBP：τ_（phos）= 496μs，φ_（phos）= 0.15; PdPh4TBP：τ_（phos）= 258μs，φ_（phos）= 0.08）。似乎π延伸能够平衡非平面形变对Pd卟啉三重态发射率的有害影响。

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