荧光猝灭研究芳醚树枝形聚合物构象

本工作分别合成了外围修饰一个芘基团和核心修饰一个芘基团两个系列的芳醚树枝形聚合物Py-Gn-OH和Gn-CH₂-Py(n=1~4)。Py-Gn-OH和Gn-CH₂-Py的发光随代数增加而增强,荧光寿命增加。荧光猝灭实验结果表明,树枝形聚合物Py-Gn-OH和Gn-CH₂-Py的双分子猝灭速率常数均随代数增加而减小,表明树枝形聚合物发生了构象折叠,位于核心和外围的芘基团均被树枝形聚合物骨架包裹,随代数增加树枝形聚合物骨架增大,对芘基团包裹作用增强,导致猝灭剂接近芘基团的位阻增大。Gn-CH₂-Py体系的双分子猝灭速率常数均比相应代数Py-Gn-OH体系略小,说明树枝形聚合物骨架对连接在核心的芘基团的包裹程度比对连接在外围的芘基团略强。本工作为新型功能芳醚树枝形聚合物设计和应用提供了参考。     

芳醚双枝树枝形聚合物体系的设计合成及三重态能量传递和电子转移的研究

树枝形聚合物的结构特点和良好的可修饰性使其在模拟光捕获体系研究中受到广泛重视,本论文设计合成了两个系列的双枝芳醚树枝形聚合物,通过光物理以及光化学方法研究了芳醚树枝形聚合物体系三重态能量传递和三重态电子转移过程:1.设计合成了两个系列的芳醚树枝形聚合物体系.合成了1代到3代外围以二苯酮基团修饰、核心以降冰片二烯基团修饰的双枝芳醚树枝形聚合物([BP-Gn]₂-NBD,n=1-3)及相应的异构化产物([BP-Gn]₂-QC,n=1-3);合成了外围和核心分别修饰二苯酮和萘的双枝芳醚树枝形聚合物([BP-Gn]₂-NA,n=1-4),及相应的给体模型化合物([BP-Gn]₂-BEN,n=1-4),及相应的给体模型化合物([BP-Gn]-2BEN,n=1)4),共16个新化合物.     

芘和蒽作为荧光探针探测树枝形聚合物微环境

分别以芘和(9-蒽基)甲基三甲基溴化铵(An)作为荧光探针研究了一系列羧基为外围末端基团的芳醚树枝形聚合物Gn(n=1-4)的内部微环境极性及包结情况. 芘荧光I1/I3值在1-3代树枝形聚合物钾盐水溶液中变化不大, 而3到4代有一个陡降, 推测1-3代树枝形聚合物处于相对开放的结构, G4为相对密闭的球形结构, 4代树枝形聚合物表现出更好的包结特性. An在树枝形聚合物G2钾盐水溶液中的荧光光谱结果表明, 树枝形聚合物G2可以包结两个以上的An分子, An分子疏水的蒽环部分位于树枝形聚合物内部孔穴中, 而带正电荷的铵离子靠近树枝形聚合物分子的极性末端.     

芳醚树枝形聚合物体系中电子转移和能量传递研究

树枝形聚合物英文名为dendrimer,是具有类似树枝状结构的化合物,由核心、内层支化单元和外围基团三部分组成.树枝形聚合物具有与光合作用体系相似的结构,作为模拟光合作用体系被广泛研究.电子转移是光合作用中的重要过程,研究树枝形聚合物体系中的电子转移与能量传递具有重要的意义.本论文设计合成了一系列芳醚树枝形聚合物,用光物理和光化学方法研究了芳醚树枝形聚合物体系中电子转移和能量传递过程,得到了一系列有意义的结果.     

外围萘修饰PAMAM树枝形聚合物的合成及其质子化过程研究

合成了外围修饰有萘基团的0～3代聚酰胺-胺树枝形聚合物GnN (n＝0～3), 化合物通过了IR, 1H NMR, 13C NMR和MALDI TOF的表征. 稳态光物理研究表明, 甲醇溶液中GnN外围萘基团与骨架胺之间发生电子转移过程, 形成最大发射峰在450 nm的激基复合物, 萘的荧光被明显猝灭; 当GnN骨架被质子化, 分子内光致电子转移过程和萘与骨架胺基间激基复合物的形成被抑制, 萘单体荧光发射大大增强; 由于质子化后树枝形聚合物骨架趋于伸展构象, 外围萘基团间相互作用增强, 部分形成最大发射峰在400 nm的激基缔合物.     

芳醚树枝形聚合物体系的设计合成及电子转移和三重态能量传递研究

<正>树枝形聚合物是一类具有特殊结构的大分子,通过可控合成,具有光捕获功能的官能团可以精确地分布在树枝形聚合物的核心或外围,甚至可以在支化单元的任何位置,随着代数的增加,官能团数目从核心向外围呈指数增长,树枝形聚合物的这种特殊结构被用来模拟光合作用中的光捕获体系.电子转移和能量传递是光合作用的关键过程,也是光化学研究的重要内容,因此,研究树枝形聚合物体系内的电子转移和能量传递是人工模拟光合作用的一个突破口,是目前相关研究工作的热点之一.本文设计合成了一系列一代到四代的芳醚树枝形聚合物,共24个新化合物,通过稳态、瞬态以及光化学反应的方法研究了芳醚树枝形聚合物体系内电子转移和三重态能量传递过程,得到了一系列有意义的研究结果:     

尼罗红为探针对芳醚树枝形聚合物微环境的研究

本工作合成了一系列羧基为外围末端基团的芳醚树枝形聚合物Gn(n=1—4),利用吸收光谱,稳态和时间分辨荧光发射光谱研究了Gn对尼罗红分子的增溶作用和Gn微环境极性.研究结果表明,尼罗红在Gn中的溶解度随代数增加而增大,从G1到G4,尼罗红溶解度相比水中分别增加了3、35、47和215倍.Gn的微环境极性比水低,2-4代芳醚树枝形聚合物具有相似的微环境极性.     

水溶性树枝形聚合物微反应器笼效应研究

本工作以羧基为末端基团的芳醚树枝形聚合物G_n(n=1-4)和核心为十二烷基链的聚酰胺-胺树枝形聚合物PG_m(m=1-3)作为光化学微反应器,研究了1-苯基-3-对甲苯基丙酮在水溶液中的α-光解反应,并计算了笼效应.研究结果表明,芳醚树枝形聚合物G_n的笼效应随代数增加而增大,高代数树枝形聚合物表现出对底物分子更强的限制性作用,增加树枝形聚合物的浓度可以提高笼效应;聚酰胺-胺树枝形聚合物PG_m对CH₃-DBK的限制作用远低于芳醚树枝形聚合物G_n.     

葫芦[7]脲与紫精和香豆素修饰树枝形分子的分步结合及对体系发光性质的调控

合成了外围修饰香豆素PAMAM树枝形分子Gm-2(m+1)C, 外围和核心分别共价连接香豆素和紫精的树枝形分子EV-Gm-2(m+1)C (m=0, 1), 以及香豆素和紫精的模型化合物C-Model和EV, 化合物均通过了¹H NMR, IR和MALDI-TOF MS的鉴定. ¹H NMR和光物理研究结果表明, 在pH=4.5的醋酸-醋酸钠缓冲溶液中, CB[7]与紫精和树枝形分子外围的香豆素基团均可形成1:1的包结复合物, 结合常数分别为3.3×10⁶ mol^-1·L和1.4～1.6×10⁵ mol^-1·L. 香豆素基团中7位二乙氨基及取代侧部分香豆素环包裹在CB[7]刚性的疏水空腔内, 包结复合物的形成限制了香豆素7位N,N'-二乙氨基的扭转, 抑制了香豆素基团从发光的分子内电荷转移(ICT)态向不发光的扭曲的分子内电荷转移(TICT)态的转变, 而且CB[7]内腔的疏水环境有利于香豆素ICT态辐射跃迁, 使体系发光大大增强. EV-Gm-2(m+1)C与CB[7]的主客体作用为分步结合机制, 加入的CB[7]先与紫精基团作用形成包结复合物, 待体系中紫精基团与CB[7]结合后, 体系中香豆素基团再与CB[7]作用形成包结复合物. 无论是Gm-2(m+1)C还是EV-Gm-2(m+1)C体系, 均可以通过加入CB[7]的量调节体系中香豆素基团与CB[7]形成包结复合物的多少, 从而实现对Gm-2(m+1)C和EV-Gm-2(m+1)C体系发光的调控. 本工作为可调控发光树枝形聚合物的发展提供了一种新的策略.     

聚集诱导发光基团修饰的功能化树枝形聚合物及其光物理性质研究

构筑和发展新型光功能树枝形聚合物是当前研究热点之一. 聚集诱导发光(Aggregation Induced Emission. AIE)类化合物以其高固态发光量子产率和广阔的应用前景引起研究者的极大关注, 分子内旋转受限降低了非辐射失活被认为是AIE高固态发光量子产率的主要原因. 在树枝形聚合物的外围修饰聚集诱导发光基团, 改善树枝形聚合物的发光性能, 通过外界环境改变树枝形聚合物分子构象, 实现对功能化树枝形聚合物体系发光的调控, 对扩展光功能树枝形聚合物在发光材料以及光捕获体系中的应用有重要意义.     

Conversion of intramolecular singlet electron transfer at room temperature into triplet energy transfer at 77 K: photoisomerization in norbornadiene- and carbazole-labeled poly(aryl ether) dendrimers

A series of Fréchet-type poly(aryl ether) dendrimers (CZ-Gn-NBD, n = 1-3) with carbazole (CZ) chromophores and a norbornadiene (NBD) group attached to the periphery and the core, respectively, were synthesized, and their photophysical and photochemical properties were investigated. Selective excitation of the carbazole units in CZ-Gn-NBD resulted in a singlet electron transfer from CZ to NBD at room temperature, and an intersystem crossing followed a triplet-triplet energy transfer from CZ to NBD in glassy 2-methyltetrahydrofuran at 77 K. Both singlet electron transfer and triplet energy transfer processes lead to the isomerization of the norbornadiene group into the quadricyclane (CZ-Gn-QC). The efficiencies and the rate constants for singlet electron transfer are approximately 88, 80, and 74% and 1.8 x 10(9), 6.1 x 10(8), and 4.0 x 10(8) s(-1) for generations 1-3, respectively. The quantum yields of the intramolecular photosensitized isomerization are measured to be approximately 0.013, 0.012, and 0.011, and the efficiencies of triplet norbornadiene formation via singlet electron transfer are approximately 0.070, 0.065, and 0.059 for generations 1-3, respectively. The light-harvesting ability of CZ-Gn-NBD increases with the generation due to an increase of the number of peripheral chromophores. In glassy 2-methyltetrahydrofuran at 77 K, the triplet-triplet energy transfer proceeds with efficiencies of approximately 0.86, 0.64, and 0.36 and rate constants of 0.96, 0.25, and 0.08 s(-1) for generations 1-3, respectively. The intramolecular singlet electron transfer and triplet energy transfer in CZ-Gn-NBD proceed mainly via a through-space mechanism involving the proximate donor (folding back conformation) and acceptor groups.     

蒽-对二氰基乙烯基苯激基复合物的形成与能量传递

本文设计合成了三个以不同链长相连接的蒽-对二氰基乙烯基苯(An-DCVB)化合物。利用吸收光谱,荧光光谱,激光闪光光解和单光子计数器等证实An-DCVB受光激发,发生分子内电子转移,生成激基复合物且发现有三重态能量传递,描述了分子内电子转移的主要途径,研究并探讨了An-DCVB的三种不同连接链长对分子构象,激基复合物的形成以及三重态能量传递的影响。     

以尼罗红为探针对新型两亲性树枝形聚合物微环境的研究

本工作合成了一系列外围以三缩四乙二醇单甲醚修饰的烷基芳醚骨架两亲性树枝形聚合物Gn(n=0—3),化合物通过了¹H-NMR,IR和MALDI-TOF-MS的表征.利用吸收光谱,稳态和时间分辨荧光光谱研究了水溶液中Gn对尼罗红分子的增溶作用以及Gn内部微环境的极性.研究结果表明,高代数树枝形聚合物Gn对尼罗红具有更好的增溶效果.1—3代树枝形聚合物Gn内部疏水孔腔微环境极性随代数增加而逐渐降低,G1和G2树枝形聚合物具有相似的微环境极性,而由于构象的变化使G3具有更加疏水的微环境.     

Energy and electron transfer in bifunctional non-conjugated dendrimers

Nonconjugated dendrimers, which are capable of funneling energy from the periphery to the core followed by a charge-transfer process from the core to the periphery, have been synthesized. The energy and electron donors involve a diarylaminopyrene unit and are incorporated at the periphery of these dendrimers. The energy and electron acceptor is at the core of the dendrimer, which involves a chromophore based on a benzthiadiazole moiety. The backbone of the dendrimers is benzyl ether based. A direct electron-transfer quenching of the excited state of the periphery or a sequential energy transfer-electron-transfer pathway are the two limiting mechanisms of the observed photophysical properties. We find that the latter mechanism is prevalent in these dendrimers. The energy transfer occurs on a picosecond time scale, while the charge-transfer process occurs on a nanosecond time scale. The lifetime of the charge separated species was found to be in the range of microseconds. Energy transfer efficiencies ranging from 80% to 90% were determined using both steady-state and time-resolved measurements, while charge-transfer efficiencies ranging from 70% to 80% were deduced from fluorescence quenching of the core chromophore. The dependence of the energy and charge-transfer processes on dendrimer generation is analyzed in terms of the backfolding of the flexible benzyl ether backbone, which leads to a weaker dependence of the energy and charge-transfer efficiencies on dendrimer size than would be expected for a rigid system.     

Unsurpassed cage effect for the photolysis of dibenzyl ketones in water-soluble dendrimers

Amphiphilic water-soluble poly(alkyl aryl ether) dendrimers Gn (n = 1-3) with charge-neutral tetraethylene glycol monomethyl ethers at their periphery were synthesized as microreactors to control the photochemical reactions of dibenzyl ketone derivatives in aqueous solutions. Photophysical studies demonstrated that Gn can encapsulate organic molecules and provide a hydrophobic microenvironment. The product distribution of photolysis of dibenzyl ketone derivatives can be successfully controlled by encapsulating the substrates within dendrimers, and an unsurpassed cage effect of 1.00 is reached in high generation dendrimers, revealing that a thick and compact "shell" was formed at the periphery of the dendrimers. The cage effect is also significantly influenced by the substituent at the para-position of the guest molecules. The higher generation dendrimers exhibit a better confined microenvironment and the aggregates possess more compact cavities to "lock" the guests than the corresponding unimolecular dendrimers. After photolysis, the separation of products can be easily achieved by extracting from the dendrimer solutions and the dendrimers are simply recovered and reused.     

Exciplex fluorescence emission from simple organic intramolecular constructs in non-polar and highly polar media as model systems for DNA-assembled exciplex detectors

Organic intramolecular exciplexes, N-(4-dimethylaminobenzyl)-N-(1-pyrenemethyl)amine (1) and N'-4-dimethylaminonaphthyl-N-(1-pyrenemethyl)amine (2), were used as model systems to reveal major factors affecting their exciplex fluorescence, and thus lay the basis for developing emissive target-assembled exciplexes for DNA-mounted systems in solution. These models with an aromatic pyrenyl hydrocarbon moiety as an electron acceptor appropriately connected to an aromatic dimethylamino electron donor component (N,N-dimethylaminophenyl or N,N-dimethylaminonaphthyl) showed strong intramolecular exciplex emission in both non-polar and highly polar solvents. The effect of dielectric constant on the maximum wavelength for exciplex emission was studied, and emission was observed for 1 and 2 over the full range of solvent from non-polar hydrocarbons up to N-methylformamide with a dielectric constant of 182. Quantum yields were determined for these intramolecular exciplexes in a range of solvents relative to that for Hoechst 33,258. Conformational analysis of 1 was performed both computationally and via qualitative 2D NMR using (1)H-NOESY experiments. The results obtained indicated the contribution of pre-folded conformation(s) to the ground state of 1 conducive to exciplex emission. This research provides the initial background for design of self-assembled, DNA-mounted exciplexes and underpins further development of exciplex-based hybridisation bioassays.     

Light-harvesting and photoisomerization in benzophenone and norbornadiene-labeled poly(aryl ether) dendrimers via intramolecular triplet energy transfer

A series of benzophenone (BP) and norbornadiene (NBD)-labeled poly(aryl ether) dendrimers (Gn-NBD), generations 1-4, were synthesized, and their photophysical and photochemical properties were examined. The phosphorescence of the peripheral BP (donor) chromophore was efficiently quenched by the NBD (acceptor) group attached to the focal point. Time-resolved spectroscopic measurements indicated that the lifetime of the triplet state of the BP chromophore was shortened due to the proximity of the NBD group. Selective excitation of the BP chromophore resulted in isomerization of the NBD group to quadricyclane (QC). All of these observations suggest that an intramolecular triplet energy transfer occurs in Gn-NBD molecules. The light-harvesting ability of these molecules increases with generation due to an increase in the number of peripheral chromophores. The energy transfer efficiencies are ca. 0.97, 0.54, 0.45, and 0.37 for generations 1-4, respectively, and the rate constant of the triplet-triplet energy transfer is ca. 10(6)-10(7) s(-1), which decreases inconspicuously with increasing generation. The intramolecular triplet energy transfer is proposed to proceed mainly via a through-space mechanism involving the closest donor (folding back conformation) and acceptor groups.