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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Intervalence charge transfer in mixed valence compound modified by the formation of a supramolecular complex.
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Intervalence charge transfer in mixed valence compound modified by the formation of a supramolecular complex.

机译：通过形成超分子复合物而修饰的混合化合价化合物中的化合价电荷转移。

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摘要

The electrochemical and spectroelectrochemical properties of N,N-diphenyl-1,4-phenylenediamine (PDA) were investigated in the absence and in the presence of 18-crown-6-ether (18C6) or dibenzo 24-crown-8-ether (DB24C8), in a solution of tetrabutylammonium hexafluorophosphate (TBAPF6) in acetonitrile and in the presence of trifluoroacetic acid (TFA) only for 18C6. In neutral acetonitrile, PDA undergoes two reversible oxidation processes, which lead first to the formation of the cation-radical considered as mixed valence (MV) compound, and then to the dicationic species. When 18C6 is added in the medium and depending on 18C6 concentration, cyclic voltammetry shows a marked shift to more cathodic potentials of the current waves of the second redox process only. This is attributed to a strong interaction between the PDA ~(+2) dication and two 18C6 molecules, leading to the formation of a supramolecular complex with an association constant value K _a = 7.0 × 10~ 7 M~(-2). The interaction of 18C6 with PDA ~(+2) dication has a direct effect on the PDA ~+. cation-radical corresponding to a decrease in the lifetime of the MV compound and of the intramolecular electron transfer rate when 18C6 is present. Indeed, it results in a large decrease in the intervalence charge transfer (IV-CT) between the two amine centers in the MV compound (k_(th) = 1.35 × 10 ~(10) s ~(-1) in 18C6-free neutral solution containing 5.0 × 10 ~(-4) M PDA, and k _(th) = 3.6 × 10 ~9 s~(-1_ in the same medium at [18C6]/[PDA] = 20/1). And the comproportionation constant K _(co) falls from 6.0 × 10 ~6 in 18C6-free solution to 1.6 × 10~ 3 at [18C6]/[PDA] = 20/1. In acidified acetonitrile and when TFA concentration is increased, PDA still shows the two successive and reversible oxidation processes, but both are shifted to more anodic potentials. However, when 18C6 is added, the two oxidation waves shift to more cathodic potentials, indicating an interaction of all protonated PDA redox states with 18C6, resulting in the formation of supramolecular complexes. In the presence of TFA, the value of K _(co) is decreased to 4.3 × 10 ~4, but it remains unchanged when 18C6 is added, indicating no change in the lifetime of the MV compound. In this medium, IV-CT in the MV compound is greater with 18C6 (k _(th) = 2.3 × 10 ~(10) s ~(-1) for [18C6]/[PDA] = 20/1) than without (k _(th) = 1.4 × 10 ~9 s~(-1)), which indicates a more important IV-CT rate when 18C6 is present. The results show for the first time that is it possible to control the IV-CT rate, through the lifetime and the potential range where the MV compound is the most important. This control is not obtained as usual by chemical modification of the structure of the starting molecule, but by varying either the acidity or the 18C6 concentration as external stimuli, which lead to reversible formation/dissociation of a supramolecular complex species. Moreover, we also studied the electrochemical properties of PDA in the presence of wider crown ether such as DB24C8. We showed that PDA undergoes the same electrochemical behavior with DB24C8 than with 18C6 in neutral organic medium (K _a = 2.9 × 10 ~3 M ~(-1)). This result suggests that the complexation between the electrogenerated PDA ~(+2) dication and the crown ethers may occur through face-to-face mode rather than rotaxane mode even with DB24C8 which is supposed to form inclusion complexes.
机译：在不存在和存在18冠冕6-醚（18C6）或二苯并24-冠冕8-醚（18C6）的情况下研究了N，N-二苯基-1,4-苯二胺（PDA）的电化学和光谱电化学性质DB24C8）在六氟磷酸四丁基铵（TBAPF6）的乙腈溶液中，在三氟乙酸（TFA）的存在下仅用于18C6。在中性乙腈中，PDA经历了两个可逆的氧化过程，首先导致形成被认为是混合价（MV）化合物的阳离子自由基，然后形成除垢剂。当在介质中添加18C6并取决于18C6浓度时，循环伏安法显示仅第二次氧化还原过程的电流波向更大的阴极电位转移。这归因于PDA〜（+2）指示剂与两个18C6分子之间的强相互作用，从而导致缔合常数值为K _a = 7.0×10〜7 M〜（-2）的超分子复合物的形成。 18C6与PDA〜（+2）指示剂的相互作用对PDA〜+有直接影响。当存在18C6时，相应于MV化合物寿命和分子内电子转移速率降低的阳离子自由基。实际上，它导致MV化合物中两个胺中心之间的间隔电荷转移（IV-CT）大大降低（在无18C6的条件下，k_（th）= 1.35×10〜（10）s〜（-1）中性溶液，含5.0×10〜（-4）M PDA，k_（th）= 3.6×10〜9 s〜（-1_在同一介质中[18C6] / [PDA] = 20/1）。在[18C6] / [PDA] = 20/1时，配比常数K _（co）从无18C6溶液中的6.0×10〜6下降至1.6×10〜3.在酸化的乙腈中，当TFA浓度增加时，PDA仍然显示了两个连续且可逆的氧化过程，但都转移到了更多的阳极电势，但是，当添加18C6时，两个氧化波转移到了更多的阴极电势，表明所有质子化的PDA氧化还原态都与18C6相互作用，从而在存在TFA的情况下，K _（co）的值降低至4.3×10〜4，但在添加18C6时其值保持不变，表明M的寿命没有变化。 V化合物。在这种介质中，MV化合物中的18C6的IV-CT值比不使用18C6时的更大（k [（th）= 2.3×10〜（10）s〜（-1），[18C6] / [PDA] = 20/1） （k_（th）= 1.4×10〜9 s〜（-1）），表明当存在18C6时，IV-CT速率更为重要。结果首次表明，可以通过MV化合物最重要的寿命和电位范围来控制IV-CT速率。通常不能通过化学修饰起始分子的结构来获得这种控制，而是通过改变酸度或18C6浓度作为外部刺激，从而导致超分子复合物物种的可逆形成/离解。此外，我们还研究了在较宽的冠醚（例如DB24C8）存在下PDA的电化学性能。我们表明，在中性有机介质中，DB24C8与18C6相比，PDA的电化学行为相同（K _a = 2.9×10〜3 M〜（-1））。该结果表明，即使被认为会形成包合物的DB24C8，也可能通过面对面模式而不是轮烷模式来发生电产生的PDA〜（+2）阳离子和冠醚之间的络合。

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