液相体系下激发态分子内超快动力学实验与理论研究

发布时间：2018-05-08 22:18

本文选题：液相 + 激发态　；参考：《吉林大学》2016年博士论文

【摘要】：分子激发态超快动力学过程一直是原子与分子物理领域关注的热点问题。众所周知,自然环境中大多数的化学现象和生命活动都是在液相体系下进行的,研究液相体系特别是液相中大分子复杂体系对于人们了解自然界中基本光物理、光化学过程的机制非常重要。值得注意的是,许多重要的光物理、光化学过程都涉及分子的激发态,例如生物分子中广泛存在的激发态质子转移、电荷转移等,这就为研究液相中大分子复杂体系的激发态超快过程赋予了特殊的意义。在本文中,我们应用飞秒瞬态吸收光谱实验技术结合含时密度泛函理论计算方法针对几种液相体系的激发态分子内超快动力学过程进行了研究。主要内容概括如下:(1)应用密度泛函/含时密度泛函(DFT/TDDFT)理论方法针对Salicylaldehyde(SA)分子的激发态分子内质子转移过程(ESIPT)进行了研究。结果表明,SA分子在被激发到第一电子激发态(S1)后会发生ESIPT现象,证实了Stock关于SA分子在环己烷(CHX)溶剂中超快实验的推测[1],并且揭示了SA分子特殊的单荧光特性来源于其S1态只有一个异构化的稳定结构,即只存在酮式(keto*)结构,烯醇式结构(enol*)在S1态并不存在。此外,计算结果还说明了由分子内电荷再分布导致的羰基氧电负性变化是SA分子发生ESIPT现象的原因。(2)我们对1-hydroxypyrene-2-carbaldehyde(HP)分子及其衍生物1-methoxypyrene-2-carbaldehyde(MP)分子在环己烷(CHX)溶剂中的超快过程进行了实验与理论研究。稳态光谱实验表明,MP分子有明显的荧光属性而HP分子却具有无荧光特性。应用飞秒瞬态吸收光谱实验方法观测了HP分子与MP分子的激发态超快动力学过程。实验结果拟合表明,HP分子存在两个超快过程,分别为激发态分子内质子转移过程(ESIPT)与系间窜越过程(ISC);而MP分子只有一个溶质—溶剂相互的超快过程。在此基础上,采用DFT/TDDFT方法对HP分子进行了理论计算,获得了势能曲线、红外光谱等相关信息,证实了HP分子被激发到S1态后先经历ESIPT过程,随后发生ISC过程。结合飞秒瞬态吸收光谱与TDDFT理论计算结果,发现ISC过程的发生是HP分子荧光猝灭的原因。(3)应用高压瞬态吸收光谱技术结合DFT/TDDFT理论方法,研究了高压对香豆素510(C510)分子在乙腈(ACN)溶剂中激发态扭转分子内电荷转移(TICT)过程的影响,压力范围是常压到0.3 GPa。通过对C510体系常压下的分子性质进行计算,我们获得了基态、第一电子激发态(S1)态的几何构型以及电荷分布,证明了该分子被激发到S1态后会发生TICT过程。在此基础上,应用高压瞬态吸收方法观测了压力对C510分子TICT过程的影响。结果表明,随着压力的提高相应的溶剂粘度系数也增大,但是C510分子TICT过程却反常地变快,并伴随着荧光寿命的变短。通过实验与理论研究,本文把上述新颖现象产生的原因分别归属于C510分子被激发后基团的反转(使分子整体更加趋于平面)以及压力导致的基态与激发态之间能隙变小。
[Abstract]:The ultrafast kinetic process of molecular excited states has always been a hot issue in the field of atomic and molecular physics. It is well known that most of the chemical phenomena and life activities in the natural environment are carried out under the liquid phase system. The study of the liquid phase system, especially the large molecular complex in the liquid phase, has been used to understand the basic optical physics in nature, The mechanism of photochemical process is very important. It is worth noting that many important photophysical and photochemical processes involve the excited state of molecules, such as the excited state proton transfer and charge transfer, which are widely existed in the biomolecules. This has given special significance to the study of the excite ultrafast process in the complex system of large molecules in the liquid phase. In this paper, we use femtosecond transient absorption spectroscopy (femtosecond transient absorption spectroscopy) technique and time-dependent density functional theory to study the intramolecular ultrafast dynamic processes of several liquid phase systems. The main contents are as follows: (1) the application of density functional / time density functional (DFT/TDDFT) theory to Salicylaldehyde (SA) molecules The intron transfer process (ESIPT) of the excited state molecules (ESIPT) has been studied. The results show that the ESIPT phenomenon occurs after the SA molecule is excited to the first electron excited state (S1), which confirms the Stock about the ultra fast experiment of the SA molecule in the cyclohexane (CHX) solvent and reveals that the special single fluorescence characteristic of the SA molecule comes from the only one of the S1 states. The stable structure of isomerization is only a ketone (keto*) structure and the enol structure (enol*) does not exist in the S1 state. In addition, the results also show that the negative changes in carbonyl oxygen caused by the redistribution of intramolecular charge redistribution are the reasons for the ESIPT phenomenon of the SA molecule. (2) we are on the 1-hydroxypyrene-2-carbaldehyde (HP) molecule and its derivatives. The ultrafast process of 1-methoxypyrene-2-carbaldehyde (MP) molecule in the solvent of cyclohexane (CHX) has been studied experimentally and theoretically. The steady-state spectral experiments show that the MP molecules have obvious fluorescence properties while the HP molecules have no fluorescence characteristics. The ultrafast dynamics of the excited states of HP and MP molecules are observed by the experimental method of femtosecond transient absorption spectroscopy. The experimental results show that there are two ultrafast processes in the HP molecule, which are the transition process of the excited state intramolecular endoplasmic reticulum (ESIPT) and intersystem channeling (ISC), and the MP molecule has only one solute solvent super fast process. On this basis, the DFT/TDDFT method is used to calculate the HP molecule, and the potential energy curve is obtained. The infrared spectrum and other related information confirmed that the HP molecule was excited to the S1 state after the ESIPT process and then the ISC process. Combining the femtosecond transient absorption spectrum and the TDDFT theoretical calculation, it was found that the occurrence of the ISC process was the cause of the fluorescence quenching of HP molecules. (3) the application of high pressure transient absorption spectroscopy combined with the DFT/TDDFT theoretical method. The effect of high pressure on the torsional intramolecular charge transfer (TICT) process of the excited state of coumarin 510 (C510) molecule in acetonitrile (ACN) solvent. The pressure range is calculated by the atmospheric pressure to 0.3 GPa. by the molecular properties under the atmospheric pressure of the C510 system. We have obtained the ground state, the geometry configuration of the first electron excited state (S1) state and the charge distribution. On the basis of the high pressure transient absorption method, the effect of pressure on the TICT process of C510 molecule is observed by high pressure transient absorption. The result shows that the corresponding viscosity coefficient of the solvent increases with the increase of pressure, but the TICT process of the C510 molecule becomes faster and faster, with the shorter fluorescence lifetime. Through real time, the C510 molecule has a short time of the C510. In the laboratory and theory study, the causes of the above novel phenomena are attributed to the reversal of the group after the C510 molecule is excited (making the whole molecule more flat) and the gap between the ground state and the excited state caused by the pressure is smaller.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O561

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