付红兵
论文题目：有机超微粒的制备及其尺寸效应的研究
作者简介：付红兵，男，1971年03月出生，1998年09月师从于中国科学院化学研究所姚建年教授，于2001年07月获博士学位。
摘 要
有机和无机半导体之间的本质差别在于带宽或轨道重叠程度。有机分子晶体中的弱相互作用〔范德华力、氢键〕和小的激子半径〔Frenkel激子、电荷转移激子〕决定了有机超微粒的介观尺寸效应具有区别于无机纳晶的独特性。迄今为止，关于有机超微粒尺寸效应的研究，以及无机纳米晶体研究领域已建物理模型在有机领域的普适性问题都还甚少报道，但唯此我们才有抢占制高点的机会。本文以系列吡唑啉化合物作为目标分子，合成得到了一系列大小和形状可调的、高度单分散的纳米超微粒。进一步，通过稳态和瞬态光谱研究了有机超微粒的介观尺寸依赖特性，并结合分子模拟对其本质进行了解释。我们的研究表明有机超微粒同样具有显著的尺寸效应，为进一步研究有机和无机领域介观尺寸效应的异同点奠定了坚实的基础。而且对有机分子在介观尺度下的特异性的研究，可以加深我们理解有机分子晶体这类传统材料中的许多基本过程和现象，对于我们发展现有理论进一步开发和利用有机分子晶体〔如：有机导体、有机发光器件等〕有着重要意义。具体结果如下：
1、利用再沉淀法，通过控制温度、浓度和沉积时间等动力学因素，制备得到了粒径从几十到数百纳米的球形1-苯基-3-(对N,N-二甲基-苯乙烯基)-5-(对N,N-二甲基-苯基)-2-吡唑啉〔PDDP〕超微粒和方块形状的1,3,5-三苯基-2-吡唑啉〔TPP〕纳米晶体。我们研究证实了PDDP超微粒和TPP纳晶表现出的尺寸效应均起源于随着尺寸的增大逐渐形成的分子间电荷转移〔CT〕激子。吸收谱中的短波部分来自于局限在单个分子上的Frenkel激子的贡献，长波区域的吸收峰则出自超微粒中分子紧密堆积引起的电荷转移激子，并进一步为瞬态荧光测试证明。随着超微粒粒径的增大，CT态的吸收峰逐渐出现，而且由于激子的限域效应向长波移动。超微粒中，S1态和CT态是平衡的，它们之间的能级间隙随着超微粒尺寸增大而减小。增大微粒的尺寸时从S1态到CT态的荧光发射强度再分布表明，S1态和CT态互相竞争并同时受纳米超微粒尺寸的影响。
2、观察到了球形的1,3-二苯基-5-芘基-2-吡唑啉〔DPP〕超微粒由于高度的单分散性而自组织排列成有序的二维阵列。DPP分子在溶液中只表现出芘的发射特征；在发光器件即固态薄膜中却只观察到了470
nm处吡唑啉环的发射特征。但是，DPP超微粒则表现出了分别出自于芘环386
nm、吡唑啉环465 nm和分子之间的吡唑啉环-芘环电荷转移激子570
nm的三重发射，而且各自对应各自的激发光谱，即三重发射的光通道互不干涉。在粒径确定时，用一确定波长激发时，发射光谱中不同发射的最大强度直接决定于对应激发光谱在该波长下的强度。另一方面，超微粒粒径的大小同样影响着三个部分的相对强度。随着粒径的增大，吡唑啉环-芘环之间电荷转移态570
nm的荧光发射逐渐消失。这意味着，在实际当中通过控制粒径和变换激发波长，我们可以控制DPP超微粒的发射波长，而且DPP超微粒的自组织阵列对构建发光器件极有意义。
3、利用目标分子1,3-二苯基-2-吡唑啉〔DP〕和十六烷基三甲基溴化铵〔CTAB〕活性剂分子的相互作用，我们成功制备了直径可调的纤维状DP超微粒。XRD射线衍射证明DP分子在超微粒中有序排列；光谱数据证明DP分子的聚集体为J-聚体形式。当固定DP分子在体系中的浓度时，改变CTAB的浓度，可以控制DP分子的聚集状态。在CTAB分子和DP分子的比值N大于45时，每个CTAB胶束可以热力学稳定的溶解两个DP分子。随着N的降低，溶解在胶束中呈现单分子态的分子数目减少，处于聚集态的DP分子数目增加。N=40时，DP分子聚集形成小的颗粒；N=27时，小颗粒之间连接开始形成纤维；N<27时，纤维完全形成，N=18和9的纤维直径分别为140和225
nm且直径几乎单分散分布。在与之对应的光谱中，J-聚体吸收峰逐渐出现；室温下发射峰宽度变窄，振动能级展现；77
K下，单分子态发射强度逐渐降低，出自J-聚体能级的发射强度逐渐增强。换言之，DP超微粒表现出的尺寸依赖特性起源于DP分子的聚集体的形成。
关键词：有机超微粒，纳米纤维，尺寸依赖性，吡唑啉
Preparation of Organic Nanoparticles and its
Size Effects
Abstract
Preparation and the size-dependence of organic nanoparticles are not investigated as well as those of inorganic quantum dots by far. In this thesis, using the pyrazoline derivatives as the model compound, a series of highly monodisperse nanoparticles with controlled size and shape had been prepared. Further, their optical size-dependent properties were studied by means of steady state and time-resolved spectroscopy, and were explained by the aggregate theory using molecular modeling calculations. The optical size effects exhibited by pyrazolines nanoparticles may prove useful in the future luminescence applications, and in the study of the fundamental process connecting both of these more conventional classes of materials, i.e., organic molecular crystals (OMCs).
1. Global nanoparticles of 1- phenyl – 3 - ((dimethylamino)styryl) -5- ((dimethylamino)phenyl) - 2 - pyrazoline (PDDP) and cubic nanoparticles of 1,3,5-triphenyl-2-pyrazoline (TPP)ranging from tens to hundreds nanometers were prepared using the reprecipitation method. Their excitonic transitions responsible for absorption and emission as compared with that of dilute solution have been investigated as a function of nanoparticle size. We found that PDDP and TPP nanoparticles possess a special size-dependence in optical properties. We identified an extended charge-transfer state stemming from the model-molecules closely stacking in nanoparticles and observed it shift to high-energy side with decreasing nanoparticle size due to exciton confinement. At the same time, the molecular p-p* absorption of nanoparticles were also blue-shifted, accompanied by a hardly changing n-p* absorption as a result of the reduced overlap of the pyrazoline ring p orbital and a decrease of intermolecular interactions. Moreover S1 and CT states were in equilibrium in the nanoparticles, and the probability of fluorescence from S1 increased with decreasing nanoparticle size.
2. 1,3-Diphenyl-5-pyrenyl-2-pyrazoline (DPP) shows the emission characteristics of pyrene in solution or the emission characteristics of pyrazoline in films and bulk crystals. However, DPP nanoparticles were found to present multiple emission from pyrene at 385 nm, pyrazoline at 465 nm and an intermolecular pyrazoline-pyrene charge-transfer (CT) state at 570 nm, and each of them possesses individual optical channel. Moreover, the emission at 570 nm gradually vanished with increasing nanoparticle size due to the destroying of intermolecular pyrazoline-pyrene pair as a result of the formation of intermolecualr pyrazoline- pyrazoline pair.
3. Nanosized fiber of 1,3-diphenyl-2-pyrazoline (DP) was prepared using the templates of cetyltrimethylammonium (CTAB) micelles. Upon controlling the specific value between DP and CTAB molecules, N=nCTAB/NDP, the diameter of DP nano-fiber can be controlled. For example, when N=18 and 9, the diameters of DP nano-fiber are 140 and 225 nm, respectively. XRD measurements indicated that DP molecules are highly ordered in nano-fiber, and arrange as J-aggregate of which the absorption gradually appeared with increasing the N value and was red-shifted from that of monomer. Moreover, the decay of DP nano-fiber fluorescence became faster and the emission width became narrower than those of the dilute DP/ethanol solution due to the formation of J-aggregate in nano-fibers.
Key words: Organic Nanoparticles, Nano-fiber, Size-Dependence, Pyrazoline
