【摘要】 腙类分子开关在超分子化学领域有非常重要的应用价值,基于靛红发色团发展出的新型腙类分子开关已被合成.因其具有可见光激发下的顺反异构化特征、衍生物的易合成性及对外界刺激的敏感性,其在生物化学领域具有重要的应用价值.然而,该新型分子开关的光致异构化机制尚不明确,异构过程是否存在新奇的现象也不得而知.本文采用基于半经验OM2/MRCI的轨迹面跳跃动力学方法,系统地研究了一种名为靛红双氮二苯腙分子开关E-Z异构化过程的光致异构化机理.研究发现该E构型分子开关的S₁激发态平均寿命约为107 fs,该分子开关的E-Z异构化量子产率为16.01%.通过对该分子开关光致异构化过程的计算,明确了两种不同分子开关异构化机制;除围绕C=N键旋转的传统分子开关异构机制之外,阐明了新的异构机制——分子开关转子部分面对面的扭转;通过时间分辨的荧光辐射谱的计算,预测了异构化过程中存在极快的荧光猝灭现象,并且伴随着荧光红移的发生;通过对计算得到的荧光光谱与激发态平均寿命的分析,提出了“暗态”的存在,并对“暗态”存在的原因给出了可能的解释.研究结果可为新型分子开关的设计及应用提供理论指导作用.更多还原

【Abstract】 Hydrazone molecular switches have significant application value in supramolecular chemistry. A new type of hydrazone molecular switch, named isatin N²-diphenylhydrazone, has been synthesized. Owing to its cis-trans isomerization characteristics under visible light excitation, ease of synthesizing of derivatives, and sensitivity to external stimuli, it has important application value in the field of biochemistry. Because of its forward and backward visible light excitation characteristics, it is considered a class of compound that is very suitable for molecular switches, and it has a wide application value in fields such as biotechnology. In addition, the derivatives compound exhibits strong interactions with negative ions, which enhances its function as a molecular switch, making it a four-state molecular switch that can be achieved by a single molecule. However, the photo-induced isomerization mechanism of these new molecular switches is not yet clear, and whether there are novel phenomena in the isomerization process is also unknown. In this work, a semi empirical OM2/MRCI based trajectory surface hopping dynamics method is adopted to systematically study a photo induced isomerization mechanism based on the E-Z isomerization process of the isatin N²-diphenylhydrazones molecular switch.Optimization configuration and the average lifetime of the first excited S₁ state are obtained by using the semiempirical OM2/MRCI method of molecular switch. It is found that the average lifetime of the S₁ excited state of the E-configuration molecular switch is about 107 fs, and the quantum yield of E-Z isomerization of the molecular switch is 16.01%. By calculating the photo induced isomerization process of the molecular switch, two different isomerization mechanisms of the molecular switch are identified. In addition to the traditional molecular switch isomerization mechanism revolving around the C=N bond, a new isomerization mechanism,i.e. the face-to-face twisting of the molecular switch rotor part is elucidated. By calculating the time-resolved fluorescence radiation spectrum, it is predicted that there may be a very fast fluorescence quenching phenomenon occurring in about 75 fs in the isomerization process, slightly faster than the S₁ average decay events（107 fs）. The information about wavelength-resolved attenuation at different times is also calculated,which reflects the ultrafast fluorescence quenching process accompanied by fluorescence red shift, ranging from 2.1 × 10⁴ cm^–1 to 3.4 × 10⁴ cm^–1. By comparing the calculated fluorescence spectra with the average lifetime of excited states, the existence of “dark states” is proposed, and possible explanations for the existence of “dark states” are provided, and those “dark states” may be related to lower quantum yields. The research results can provide theoretical guidance for the design and application of new molecular switches. The ease of synthesis and sensitivity to external stimuli of its derivatives make those compounds extremely valuable in molecular switching and light measurement applications.更多还原