甲基自由基的设计合成及其发光性质和稳定性的研究

发布时间：2018-06-23 11:12

本文选题：双线态 + 共轭效应　；参考：《吉林大学》2017年硕士论文

【摘要】：稳定自由基因为其单电子的稳定存而使得其具有很多独特的性质,如顺磁性,氧化还原电位低,能隙窄等特点。因此,自1900年第一例稳定自由基报道以来,这类分子得到了广泛研究。由于自由基单电子的存在,电子的跃迁在本质上与闭壳分子有所区别,表现为无论是激发态还是基态,自由基分子都表现出双线态的特点。自由基单电子占据轨道(SOMO)上只有一个电子,所以无论是SOMO和最低未占据轨道(LUMO)还是双电子最高占据轨道(HOMO)和SOMO之间的跃迁,都是完全自旋允许的。因此研究这种区别于普通荧光(来源于单线态激子的辐射跃迁)和磷光(源自三线态激子的辐射跃迁)的双线态发光机制,不仅具有重要的科学意义,同时也为有机发光领域拓展了新的思路。然而,目前报道具有发光性质的自由基非常罕见,此外自由基的发光效率低,稳定性差。因此,如何提高自由基的稳定性和发光效率这一问题亟待解决。一般来说,增加共轭能够提高发光分子的稳定性和发光效率。因此,本文中,我们通过给一种稳定的发光中性自由基——全氯代三苯甲基自由基(PTM)——连接给、拉电子基团,研究这两种方法增加共轭效应对自由基的稳定性和发光性质的影响,并期待找到提高自由基的稳定性和发光效率的途径。首先,我们基于PTM合成了连接拉电子基团二苯甲酮(DPK)和氰基二苯基乙烯(CPE)的自由基PTM-DPK,PTM-CPE,研究利用拉电子基团增加共轭对自由基荧光和稳定性的影响。通过DFT理论计算,我们发现连接拉电子基团能够增加共轭。通过溶剂化效应,我们发现PTM-DPK,PTM-CPE和PTM一样,随着溶剂极性的增强,光谱峰位置不变。说明连接拉电子基团的自由基和PTM一样属于局域态发光,同时我们发现相较于PTM,PTM-DPK和PTM-CPE的荧光量子效率没有显著变化。说明通过连接拉电子基团增加共轭不能提高自由基的荧光量子效率。但是,通过研究PTM-DPK,PTM-CPE的光稳定性,我们发现PTM-DPK,PTM-CPE的稳定性有较大的提高,说明拉电子基团能够增加自由基的光稳定性。通过电化学研究并对比自由基380nm的特征吸收峰,我们发现PTM系列的氧化电位都很高,并且拉电子基团对氧化和还原电位的影响不大,这是因为三苯甲基和氯原子引起的强的空间位阻效应作用的结果。接着我们又研究了不同给电子能力的基团对其荧光和稳定性的影响。我们合成了连接给电子基团甲硫基苯、咔唑萘、3,5-二咔唑苯基自由基PTM-PSM、PTM-Cz N、PTM-PDCz三个连接不同给电子能力基团的自由基分子,通过DFT理论计算,我们发现给电子基团没有增加共轭效应,但是通过溶剂化效应研究发现连接给电子基团的自由基属于电荷转移发光,并且DFT计算表明电荷转移是从给体的HOMO到三苯甲基自由基的SOMO的跃迁。相较于PTM,PTM-PSM,PTM-Cz N,PTM-PDCz的荧光量子效率明显提高,比如PTM-Cz N在环己烷中的发光效率高达0.54,比PTM的0.016高了34倍。这说明连接电子给体能够提高自由基的荧光量子效率。同时我们发现PTM-PSM,PTM-Cz N,PTM-PDCz的稳定性也有巨大的提高,这说明连接给体不仅能有效提高自由基的荧光量子效率,而且也能提高自由基的稳定性。因此给电子基团是设计高稳定性高荧光量子效率的一个策略。通过电化学和理论计算研究,我们发现连接给电子基团的自由基表现出HOMO-SOMO反转的奇特性质,表现为HOMO能级位于SOMO能级之上。由于空间位阻的原因,SOMO的电位变化很小,所以如果HOMO(来自于给电子基团)能量高,就可能位于SOMO之上,并且HOMO的能量越高,SOMO与HOMO的能量差越大。因此不同的给电子基团使得SOMO的位置位于HOMO下面的程度不同,PTM-PSM在HOMO之下,PTM-Cz N在HOMO-1之下,PTM-PDCz在HOMO-3之下,同时对应的稳定性增加程度与SOMO位置对应,SOMO越往下,稳定性越高。HOMO-SOMO的反转,使得自由基分子的电子排布违反了构造原理(Aufbau Principle),出现了和部分过渡态金属,量子点类似的结果,这在有机分子中非常少见。通过研究HOMO-SOMO的反转必然能够增加人们对自由基的进一步理解。同时HOMO-SOMO的反转的D-A自由基的荧光量子效率,稳定性都大大提高。因此,这也是设计高荧光量子效率,高稳定性的自由基分子一种可行的策略。
[Abstract]:The stable free gene has many unique properties, such as paramagnetic, low oxidation-reduction potential, narrow energy gap, and so on. Therefore, since the first case of stable free radicals in 1900, this kind of molecule has been widely studied. Because of the existence of free radical mono electrons, the transition of electrons is essentially closed to the shell. The molecules are different, showing that both the excited state and the ground state show the characteristics of the double state. The free radical mono electrons occupy only one electron on the orbit (SOMO), so the transition between the SOMO and the lowest unoccupied orbit (LUMO) or the double electron highest occupying orbit (HOMO) and SOMO is fully spin allowed. Therefore, it is not only of great scientific significance but also a new way of thinking for the field of organic luminescence. However, it is reported that the free radicals with the properties of luminescence are very important. In addition, the luminescence efficiency of the free radicals is low and the stability is poor. Therefore, the problem of how to improve the stability and luminous efficiency of the free radicals is urgent. In general, the addition of conjugation can improve the stability and luminous efficiency of the luminescent molecules. Therefore, in this paper, we give a stable luminescent neutral free radical - Total chlorination three Benzyl free radical (PTM) - connect to, pull electron group, study these two methods to increase the effect of conjugation effect on the stability and luminescence properties of free radicals, and expect to find ways to improve the stability and luminescence efficiency of free radicals. First, we synthesized two benzophenone (DPK) and two cyanyl benzene based on PTM. The free radical PTM-DPK, PTM-CPE of ethylene (CPE) is used to study the effect of increasing conjugation on free radical fluorescence and stability. Through the calculation of DFT theory, we find that the connecting pull electron group can increase the conjugation. Through the solvent effect, we find that PTM-DPK, PTM-CPE and PTM are the same as the polarity of the solvent, the peak position of the spectrum. It is shown that the free radicals connected to the electron group are the same as the local state luminescence, and we found that the fluorescence quantum efficiency of the PTM-DPK and PTM-CPE has no significant change in the phase of the PTM, PTM-DPK and PTM-CPE. It is indicated that the fluorescence quantum efficiency of the free radical can not be enhanced by the addition of the electron group to the electron group. However, the optical stability of the PTM-DPK, PTM-CPE is studied. Qualitatively, we found that the stability of PTM-DPK and PTM-CPE has been greatly improved, indicating that the electron group can increase the photostability of the free radical. Through the electrochemical study and comparison of the characteristic absorption peaks of the free radical 380nm, we found that the oxidation potential of the PTM series is very high and the effect of the pullant group on the oxidation and reducing potential is little. Because of the strong steric hindrance effect of three benzyl methyl and chlorine atoms, we then studied the effects of groups with different electron giving capacity on their fluorescence and stability. We synthesized three connections that are connected to the electron group methionyl benzene, carbazole naphthalene, 3,5- two carbazole phenyl free radical PTM-PSM, PTM-Cz N, PTM-PDCz. The free radical molecules for the electronic group are calculated by the DFT theory. We find that the electron group does not increase the conjugation effect, but the free radical connected to the electronic group is attributed to the charge transfer luminescence through the solvation effect, and the DFT calculation shows that the charge transfer is from the HOMO of the donor to the SOMO of the three benzyl radical. Compared to PTM, PTM-PSM, PTM-Cz N, PTM-PDCz, the fluorescence quantum efficiency is obviously improved, for example, the luminous efficiency of PTM-Cz N in cyclohexane is up to 0.54, which is 34 times higher than that of PTM's 0.016. This indicates that the connecting electron donor can improve the fluorescence quantum efficiency of the free radical. Meanwhile, we present PTM-PSM, PTM-Cz N, and the PTM-PDCz stability is also huge. This shows that the connecting donor can not only effectively improve the fluorescence quantum efficiency of the free radicals, but also improve the stability of the free radicals. Therefore, the electronic group is a strategy for designing high stability and high fluorescence quantum efficiency. By electrochemical and theoretical calculation, we present the free radical of the group that is connected to the electronic group to show HOMO-S The peculiar property of OMO inversion shows that the HOMO level is above the SOMO level. Because of the space hindrance, the potential of SOMO changes very little, so if HOMO (from the electron group) has high energy, it may be located on the SOMO, and the higher the energy of HOMO, the greater the energy difference between SOMO and HOMO. Therefore, the different donor groups make SOMO The degree of location under HOMO is different. Under HOMO, PTM-PSM is under HOMO, PTM-Cz N is under HOMO-1, PTM-PDCz is under HOMO-3, and the corresponding stability increase corresponds to the SOMO position. The higher the SOMO goes down, the higher the stability is, the higher the.HOMO-SOMO inversion, which makes the electric subdistribution of the free radical molecules violating the principle of structure (Aufbau). A similar result with a partial transition metal, quantum dots, is very rare in organic molecules. By studying the reversal of HOMO-SOMO, it is necessary to increase people's further understanding of the free radicals. At the same time, the fluorescence quantum efficiency of the reverse D-A radical of HOMO-SOMO is greatly improved. Therefore, this is also the design of high fluorescence quantum efficiency, A feasible strategy for highly stable free radicals.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O621.22

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