新型卟啉—苝酰亚胺分子阵列的合成及光电性能研究

【作者】 王福玲；

【导师】 唐建国；

【作者基本信息】 青岛大学 ， 材料学， 2011， 博士

【摘要】 卟啉化合物是非常理想的人工光合作用研究中叶绿素分子的替代化合物,具有独特的结构与功能特性。花酰亚胺类化合物具有优良的光热和化学稳定性,化学可修饰强,具有优异的光电性能。将两者通过一定的方式连接起来构筑成卟啉-花酰亚胺分子阵列,有望获得更为优异的光电性能。本论文在对国内外卟啉-花酰亚胺分子阵列在近十几年的研究进展进行总结的基础上,展示了卟啉-苝酰亚胺分子阵列在分子光电器件特别是光电转换方面的优异性能,指出该研究领域目前存在的三个主要问题：(1)合成路线长,产率低,分子阵列的品种和数量还比较少；(2)对分子阵列的聚集态结构的研究几乎是空白；(3)目前国内外对卟啉-花酰亚胺分子阵列的光物理和光化学性能研究较多,但对这些分子阵列在光电转换器件如有机太阳能电池方面的研究很少。在此基础上提出本论文的研究思路,着重于卟啉-花酰亚胺分子阵列的设计与合成、电子结构、聚集态结构的研究和探讨,重点研究了分子阵列的电荷转移与能量传递过程,初步研究了其在光电化学电池和有机薄膜太阳能电池方面的光电转换性能。本文首先利用Sonogashira偶合反应合成制备了两种卟啉-花酰亚胺分子阵列PDI-ZnPOR2和PDI-ZnPOR4。采用傅立叶红外光谱、氢核磁共振光谱和元素分析等表征手段对中间产物及目标分子阵列的化学结构进行了详细的表征,并初步探索优化了化合物的合成条件。电喷雾电离质谱和X射线光电子能谱的结果进一步确证两种分子阵列的结构。用紫外-可见吸收光谱、电化学等方法对合成的分子阵列PDI-ZnPOR2和PDI-ZnPOR4的电子结构进行了研究。研究发现,分子阵列PDI-ZnPOR2主要显示出卟啉生色团的吸收峰,并且在长波长区出现了两个新的特征吸收峰,表明分子阵列中的卟啉基元和花酰亚胺基元在基态下存在着较强的电子相互作用；而在基态下分子阵列PDI-ZnPOR4中的卟啉基元和花酰亚胺基元之间存在弱的电子相互作用,主要表现为卟啉生色团和苝酰亚胺生色团的吸收峰的简单叠加。循环伏安曲线证明分子阵列PDI-ZnPOR2和PDI-ZnPOR4表现出可逆的氧化过程和还原过程；此外,经过计算得出分子阵列PDI-ZnPOR2的能隙为1.57 eV,而PDI-ZnPOR4的能隙为1.59 eV,窄带隙特性使两种分子阵列有望应用于有机半导体和太阳能电池领域。重点研究了分子阵列PDI-ZnPOR2(?)口PDI-ZnPOR4在稀溶液中的电荷转移与能量传递过程,并对其激发态衰变机理进行了探讨。采用430 nm单色光激发分子阵列中的卟啉生色团,分子阵列显示出微弱的卟啉生色团的荧光发射,相对于参比单体化合物,分子阵列的荧光强度显著降低,表明分子阵列中存在从卟啉基元到花酰亚胺基元的光诱导电子转移过程。当采用560 nm光激发分子阵列中的花酰亚胺生色团时,发生了苝酰亚胺基元的强烈的荧光猝灭,分子阵列主要显示出卟啉生色团的荧光,且荧光强度明显降低,这揭示了分子阵列中发生了从苝酰亚胺基元到卟啉基元的光诱导能量转移过程,使卟啉生色团处于激发态,紧接着发生了从卟啉基元到花酰亚胺基元的电荷转移过程。这些结果说明无论激发分子阵列的卟啉发色团还是花酰亚胺发色团,从卟啉基元到花酰亚胺基元之间都会发生高效的分子内电荷转移。相对于非极性溶剂甲苯,分子阵列在四氢呋喃中表现出更强烈的荧光猝灭现象,进一步证实了分子阵列在光激发下确实存在由卟啉生色团到花酰亚胺生色团的高效的电荷转移。时间分辨荧光光谱的测试结果表明分子阵列中确实发生了光诱导的分子内电子转移。利用SEM和TEM等测试手段对分子阵列在不同溶剂中的聚集态结构进行了初步研究。溶剂的极性不同,分子阵列的聚集态结构也有所不同,发生了溶剂诱导的分子聚集态的变化。XRD结果证明分子阵列是以无定形状态存在。热重分析(TG)和示差扫描量热法(DSC)结果显示出两种分子阵列具有良好的热稳定性和物理稳定性,足以满足制作太阳能电池器件的要求。分子阵列PDI-ZnPOR2和PDI-ZnPOR4具有良好的光收集性能,并且光致电子自旋共振结果表明两者在薄膜状态会发生光诱导的分子内电子传递过程,从而使两种分子阵列在光致电荷分离器件上显示出潜在的应用价值。我们利用分子阵列PDI-ZnPOR2和PDI-ZnPOR4制备了光电化学电池和有机薄膜太阳能电池,并对其光电转换性能进行了初步的研究和探讨。研究发现分子阵列PDI-ZnPOR2和PDI-ZnPOR4的膜电极表现出明显的光伏效应,在模拟太阳光照射下能产生快速和稳定的光生电流。在此基础上,采用旋涂法制备了以分子阵列PDI-ZnPOR2和PDI-ZnPOR4为活性层的单层膜太阳能电池。在AM 1.5模拟太阳光照射下,以分子阵列PDI-ZnPOR2和PDI-ZnPOR4为活性层的单层膜器件的光电转换效率很低,这主要是因为在分子阵列中核心的花酰亚胺基元周围被卟啉基元包围,导致电子传输的通道被阻断,造成电子和空穴复合猝灭的几率大大增加。对卟啉-花酰亚胺分子阵列在太阳能电池器件方面的研究工作还有待改进,因实验条件及时间限制,未能更深入的研究分子阵列的聚集态结构与器件性能之间的关系；器件的光电转换效率很低,对器件性能的优化工作还有待进一步开展。本论文在此方面的初步研究工作为卟啉-苝酰亚胺分子阵列材料在有机太阳能电池方面的研究提供了基础。更多还原

【Abstract】 Porphyrin derivatives are ideal substitutes of chlorophyll molecule in study of artificial photosynthesis, which possess unique structural and property characteristics. Perylenediimides exhibit excellent photothermal and chemical stability,they can be easily chemically modified and own outstanding photoelectric properties. Porphyirn-perylene molecular arrays are constructed by linking porphyrin and perylene moieties in a certain way, and excellent photoelectric performances will be obtained.On the basis of the recent domestic and foreign progress in the field of porphyirn-perylene molecular arrays were summarized, the review showed the promising applications of these arrays in the molecular photo-electric devices especially in the photo-electric transfer aspect, and raised three existed fundamental problems:(1) the synthetic routes are long and inefficient with low yield, as a result, there are relatively few candidates of the arrays; (2) the reports on the aggregation states of the porphyrin-perylene arrays are rare; (3) the researches on the properties of the arrays focuses on the photophysics and photochemistry characteristics, and researches on the arrays for applications to the photo-electric devices including the organic solar cells are few. A research strategy was accordingly proposed for this thesis:it emphasized on the design and synthesis of porphyrin-perylene arrays, on the investigation of the electronic structures and aggregation states, the research work mainly concerned the charge/energy transfer processes in the arrays, and the photo-to-electricity conversion properties of this arrays in photoelectrochemical cell and organic film solar cell are studied preliminarily.Using the Sonogashira coupling reaction, two novel porphyrin-perylene molecular arrays PDI-ZnPOR2 and PDI-ZnPOR4 were synthesized. The intermediate compounds and target molecular arrays was characterized by FT-IR,1HNMR and elemental analysis. The conditons of synthesis were also discussed. The chemical structures of the arrays were further proved by the results of ESI-MS and the X-ray Phtoelectron Spectroscopy.The electronic structures of the two porphyrin-perylene arrays have been investigated by the UV-vis absorption spectroscopy and cyclic voltammetry (CV). The absrorption of array PDI-ZnPOR2 mainly exhibits the features of porphyrin absorption, and it shows two additional absorption peaks in the long-wavelength region, which indicates relatively strong electronic interactions exsits between the porphyrin moiety and perylene moiety in the ground state; While the absorption of array PDI-ZnPOR4 is a simple superposion of those of the molecular components, this indicates that the electronic interaction between the molecular components in the array is weak in the ground state. The electrochemistry behavior of the two arrays showed reversible oxidation and reduction processes; In additionally, the band gap of the array PDI-ZnPOR2 and PDI-ZnPOR4 by calculation were 1.57 eV and 1.59 eV, repectively, the low band-gap feature make the the two arrays have potential applications in the fields of organic semiconductor and solar cells.Photoinduced electron-transfer and energy transfer processes of arrays PDI-ZnPOR2 and PDI-ZnPOR4 in dilute solutions have been investigated in detail, and the decay mechanism of the excited states were explored. Selectively excited porphyrin chromophore at 430 nm, molecular arrays exhibits weak porphyrin emission, and the fluorescence intensity are considerably reduced compared to the reference compound. This indicated photoinduced electron transfer process from porphyrin units to perylene units in these arrays. Exciting perylene chromophore at 560 nm, significant fluorescence quenching of the perylene moiety was observed, arrays only showed weak porphyrin emission, and compared to reference compound, the fluorescence intensity was considerably decreased. This reveals the existence of the photoinduced energy transfer processes from perylene to porphyrin, following the electron transfer process from the excited porphyrin to the perylene. These results indicated the efficient photoinduced intramolecular electron transfer processes either the porphyrin was excited or the perylene was excited. In polar solvent THF, the array exhibits much stronger queching than that in nonpolar solvent toluene, which further confirmed the existence of the efficient electron transfer porphyrin units to perylene moiety. The results of the time-resolved fluorescence spectroscopy also proved that the light induced intramolecular electron transfer really occurred in these arrays.The aggregated states of these arrays in different solvents were researched by SEM and TEM. The structures of the aggregated morphology differ with the variation of the solvents, which indicated the occurrence of the solvent-induced molecular aggregate states variation. The results of the XRD reveal the solid states of the arrays are amorphous. Measurements of thermogravimetry (TG) and differential scanning calorimetry (DSC) exhibits the two arrays has good thermal and physical stability, which satisfy the demand for preparation of organic solar cells.Molecular arrays PDI-ZnPOR2 and PDI-ZnPOR4 possess excellent light harvesting performance, the results of the lightinduced electronic spin resonance of arrays in film states indicates that lightinduced intramolecular electron transfer occurs, which makes the two arrays showing their potential applications in lightinduced charge separate devices. On these bases, we fabricated photoelectrochemical cells and organic film solar cells based on the two arrays, and made preliminarily researches on the photo-to-electric properties of these devices. Obvious photovoltaic effect of the film working electrode was discovered in the photoelectrochemical cell, and rapid and steady photocurrent was generated upon illumination by simulated solar light. Single layer solar cells using arrays PDI-ZnPOR2 and PDI-ZnPOR4 as active layer were fabricated by solution spin. Under air mass (AM) 1.5 simulated solar illumination, the power conversion efficiencies (PCE) of the single layer device using PDI-ZnPOR2 and PDI-ZnPOR4 as active layer has a much lower PCE. The reason for this poor PCE lies in that in the arrays, the perylene core was surrounded by porphyrin moieties, therefore, the transporting channel might be disrupted, which increased the recombination probabilities of the electrons and holes.The research work on solar cell devices based on the porphyrin-perylene arrays remain to be improved, and due to limits in experiment conditions and time, an in-depth study on relationships between aggregates morphology and device perfomances are needed in future studies; The photoelectric conversion efficiency is rather low, therefore, further experiments concerning optimization of device performances are under way. Preliminary research work in the respect provide basis for study in application of porphyrin-perylene arrays in organic solar cells.更多还原