Hunan Provincial Key Laboratory of Environmental Catalysis & Waste Recycling, College of Materials and Chemical Engineering, Hunan Institute of Engineering, Xiangtan 411104, China.
Molecules. 2023 Jun 27;28(13):5017. doi: 10.3390/molecules28135017.
2,4-Dihydroxybenzophenone is the most widely used molecule in the benzophenone group of UV absorbers. It is known that the UV absorption ability is dependent on the substituents. Numerous studies have shown that the strength of intramolecular hydrogen bonds is the main factor affecting this type of UV absorber. However, the effect of substituents on the formation and nature of the hydrogen bonds has not been well studied. In this work, the effect of the type of substituent and the substitution position on the absorption intensity of 2,4-dihydroxybenzophenone molecules is verified both experimentally and theoretically. The effect of substituents on the intramolecular hydrogen bonding of 2,4-dihydroxybenzophenone was investigated by DFT calculations. The results indicate that the addition of different substituents leads to various changes in the strength of the hydrogen bonding in 2,4-dihydroxybenzophenone. On the X-substitution site or the Y-substitution site, halogen groups and electron-absorbing groups such as -CN and -NO increase the strength of the hydrogen bond, while electron-giving groups such as -N(CH) and -OCH decrease the strength of the bond. For the same substituent, the one at the Y site has a higher effect on hydrogen bonding than that at the X site. By NBO analysis, it was found that the substituents would cause charge redistribution of the individual atoms of 2,4-dihydroxybenzophenones, thus affecting the formation and strength of the hydrogen bonds. Moreover, when the substituent is at the Y substitution site, the oxygen atom of the carbonyl group is less able to absorb electrons and more charge is attracted to the oxygen atom of the hydroxyl group, resulting in a larger charge difference between the two oxygen atoms and an increase of bond energy. Finally, a multiple linear regression analysis of the NPA charge number of the atoms involved in the formation of the hydrogen-bonded chelated six-membered ring was performed with the energy of the hydrogen bond and the percentage of influencing factors estimated, which were found to jointly affect the strength of hydrogen bonding. The aim of this study is to provide theoretical guidance for the design of benzophenone-based UV absorbers that absorb UV light of specific wavelength bands.
2,4-二羟基二苯甲酮是二苯甲酮类紫外线吸收剂中应用最广泛的分子。已知，紫外线吸收能力取决于取代基。大量研究表明，分子内氢键的强度是影响这类紫外线吸收剂的主要因素。然而，取代基对氢键的形成和性质的影响尚未得到很好的研究。在这项工作中，通过实验和理论验证了取代基的类型和取代位置对 2,4-二羟基二苯甲酮分子吸收强度的影响。通过 DFT 计算研究了取代基对 2,4-二羟基二苯甲酮分子内氢键的影响。结果表明，不同取代基的加入导致 2,4-二羟基二苯甲酮中氢键强度发生了不同的变化。在 X 取代位或 Y 取代位上，卤素和吸电子基团（如-CN 和-NO）增加了氢键的强度，而给电子基团（如-N(CH) 和-OCH）降低了键的强度。对于相同的取代基，位于 Y 位的取代基对氢键的影响更大。通过 NBO 分析发现，取代基会导致 2,4-二羟基二苯甲酮各个原子的电荷重新分布，从而影响氢键的形成和强度。此外，当取代基位于 Y 取代位时，羰基的氧原子吸收电子的能力减弱，更多的电荷被吸引到羟基的氧原子上，导致两个氧原子之间的电荷差增大，键能增加。最后，对形成氢键螯合六元环的原子的 NPA 电荷数进行了多元线性回归分析，估算了氢键能量和影响因素的百分比，发现它们共同影响氢键的强度。本研究旨在为设计吸收特定波长带的紫外线的基于二苯甲酮的紫外线吸收剂提供理论指导。
