Kondratenko Tamara, Ovchinnikov Oleg, Grevtseva Irina, Smirnov Mikhail, Erina Oksana, Khokhlov Vladimir, Darinsky Boris, Tatianina Elena
Department of Optics and Spectroscopy, Voronezh State University, 394018 Voronezh, Russia.
Federal State Budget Educational Institution of Higher Education "Voronezh State University of Engineering Technologies", 3394036 Voronezh, Russia.
Materials (Basel). 2020 Feb 18;13(4):909. doi: 10.3390/ma13040909.
The mechanism features of colloidal quantum dots (QDs) passivation with thioglycolic acid molecules (TGA) for cases of different luminescent properties is considered using FTIR. This problem is considered based on FTIR spectra analysis for various ionic forms of TGA. Experimental TGA molecules FTIR spectra is interpreted, basing on the data on modeling of TGA vibrational modes, realized in the framework of density functional method (DFT /B3LYP/6-31+G(d)) taking into account the vibrations anharmonicity of every functional group. This approach provides a significant improvement in the agreement between the experimental and calculated data. FTIR spectra of Ag 2 S/TGA QDs with exciton and recombination luminescence are differ from each other and B "freeB" TGA molecules. The ν ( S - H ) TGA peak (2559 cm - 1 ) disappears in FTIR spectra of Ag 2 S/TGA QD samples. This fact indicates the interactions between TGA thiol group and dangling bonds of Ag 2 S nanocrystals. Ag 2 S QDs passivation with TGA molecules leads to emergence ν a s (COO - ) (1584 cm - 1 ) and ν s (COO - ) (1387 cm - 1 ) peaks. It indicates TGA adsorption in ionic form. For Ag 2 S/TGA QDs with exciton luminescence we observed (a) significant low-frequency shift of ν s (COO - ) peak from 1388 cm - 1 to 1359 cm - 1 and high-frequency shift of ν a s (COO - ) peak from 1567 cm - 1 to 1581 cm - 1 ; (b) change in the ratio of intensities of ν a s (COO - ) and ν s (COO - ) vibrations. This feature is caused by the change in the symmetry of TGA molecules due to passivation of Ag 2 S quantum dots.For Ag 2 S/TGA QDs with recombination luminescence, the insignificant high-frequency shift of 7-10 cm - 1 for ν a s (COO - ) at 1567 cm - 1 and low-frequency shift of 3-5 cm - 1 for ν s (COO - ) at 1388 cm - 1 , probably caused by the interaction of thiol with Ag 2 S surface is observed. Using FTIR spectra, it was found that IR luminescence photodegradation is also accompanied by changes in the thioglycolic acid molecules, which capped Ag 2 S QDs. In the case of Ag 2 S QDs with exciton luminescence, the degradation process is non-reversible. It is accompanied by TGA photodegradation with the formation of α -thiol-substituted acyl radical (S-CH 2 -CO • ) TGA.
利用傅里叶变换红外光谱（FTIR）研究了巯基乙酸分子（TGA）对具有不同发光特性的胶体量子点（QDs）进行钝化的机理特征。基于对TGA各种离子形式的FTIR光谱分析来考虑这个问题。根据在密度泛函方法（DFT/B3LYP/6 - 31 + G(d)）框架下实现的TGA振动模式建模数据，并考虑每个官能团的振动非谐性，对实验测得的TGA分子FTIR光谱进行了解释。这种方法显著提高了实验数据与计算数据之间的吻合度。具有激子和复合发光的Ag₂S/TGA量子点的FTIR光谱彼此不同，且与“游离”TGA分子的光谱也不同。在Ag₂S/TGA量子点样品的FTIR光谱中，ν(S - H) TGA峰（2559 cm⁻¹）消失。这一事实表明TGA硫醇基团与Ag₂S纳米晶体的悬空键之间存在相互作用。用TGA分子对Ag₂S量子点进行钝化会导致出现νas(COO⁻)（1584 cm⁻¹）和νs(COO⁻)（1387 cm⁻¹）峰。这表明TGA以离子形式吸附。对于具有激子发光的Ag₂S/TGA量子点，我们观察到：（a）νs(COO⁻)峰从1388 cm⁻¹显著低频位移至1359 cm⁻¹，νas(COO⁻)峰从1567 cm⁻¹高频位移至1581 cm⁻¹；（b）νas(COO⁻)和νs(COO⁻)振动强度比发生变化。这一特征是由于Ag₂S量子点钝化导致TGA分子对称性改变引起的。对于具有复合发光的Ag₂S/TGA量子点，观察到νas(COO⁻)在1567 cm⁻¹处有7 - 10 cm⁻¹的微小高频位移，νs(COO⁻)在1388 cm⁻¹处有3 - 5 cm⁻¹的低频位移，这可能是由于硫醇与Ag₂S表面相互作用引起的。利用FTIR光谱发现，红外发光光降解还伴随着包覆Ag₂S量子点的巯基乙酸分子的变化。在具有激子发光的Ag₂S量子点的情况下，降解过程是不可逆的。它伴随着TGA的光降解，形成α - 硫醇取代的酰基自由基（S - CH₂ - CO•）TGA。
