Island versus Archipelago Architecture for Asphaltenes: Polycyclic Aromatic Hydrocarbon Dimer Theoretical Studies
Island versus Archipelago Architecture for Asphaltenes: Polycyclic Aromatic Hydrocarbon Dimer Theoretical Studies
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DOI：
10.1021/ef301522m
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发表时间：
2013-04-01
期刊：
影响因子：
5.3
通讯作者：
Ruiz-Morales, Yosadara
中科院分区：
文献类型：
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作者：
Alvarez-Ramirez, Fernando;Ruiz-Morales, Yosadara
为了阐明沥青质中多环芳烃（PAR）核的最可能的结构（岛或群岛）问题，考虑每个沥青质分子中两个多环芳烃交联（群岛模型）和相同的两个多环芳烃以平行方式聚集而不交联（多环芳烃相互作用的岛模型），进行了分子轨道（MO）计算。将计算得到的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）能隙（H-L能隙）与沥青质0-0带荧光发射实验数据进行了比较。H-L能隙的计算是使用密度泛函理论（DFT）二聚体优化结构（弛豫结构）在半经验ZINDO方法下进行的。该方法对实验数据进行了验证，并被证明具有良好的预测能力。计算了48种具有5-10个稠环（5 FAR-10 FAR）的多环芳烃，以及它们在大核（5 FAR-10 FAR）和大核（SFAR-10 FAR）体系中形成的二聚体（大核二聚体）中的所有可能组合。总共计算了1176个群岛结构中的系统，与Cs烷烃链交叉连接，以及1176个岛屿堆叠相互作用中的系统。此外，岛和群岛模型与48个多环芳烃，在两种架构中相互作用，与10个多环芳烃，含有1-4个稠合芳环的结构（1FAR-4FAR），因此包括960大核心（5 FAR-10 FAR）小核心（IFAR-4FAR）二聚体（大小核心二聚体）的计算。因此，在这项工作中，总共计算了3312个系统。对于这两种情况下，大型和大型小型二聚体系统，并为两种架构，岛屿和群岛，进行统计分析的结果。计算结果表明，具有群岛结构的二聚体的H-L能隙与单体的H-L能隙相似。对于岛二聚体（堆叠的二聚体）的情况，H-L间隙依赖于单体的尺寸（就稠合芳环的数目而言）和构成岛（堆叠的）二聚体的单体之间的夹层几何形状或堆叠排列的类型。堆积二聚体在大多数情况下比群岛二聚体更稳定。更高的稳定性反过来又产生更大的H-L间隙。的显着广泛的变化的能隙，0.9 eV，岛和群岛之间的大-大二聚体的架构强烈依赖于二聚体的大小和堆叠安排。在后者中，π-π相互作用起作用，但影响较小。在实验范围内的堆积岛体系一般是由相同单体组成的六方（1-1）排列的二聚体和具有平行位移（PD）排列的6 FAR-10 FAR组合，结构中主要没有峡湾或凹口。所有的PAH系统，在实验范围内的沥青质相互作用时，与任何其他PAH，形成二聚体，在岛屿或群岛架构，7 FAR多环芳烃更丰富的协议与以前的文献。当比较所有计算的二聚体（大-大和大-小）的百分比时，在两种结构中，并且其H L间隙福尔斯落在实验沥青质荧光范围内，大的大二聚体比大的小二聚体更丰富。大-大的二聚体是更丰富的20.6%的岛屿架构，由17.9%的群岛architecture.It的结论是，确实，如果两个沥青质核心多环芳烃直接绑定通过一个单键，然后光学方法，如时间分辨荧光去偏振（TRFD）的研究，将确定这是一个单一的发色团，从而模糊了岛屿与群岛之间的区别。一些分解研究可能会发现这种单键对的多环芳烃也是一个单一的实体。
To shed some light on the problem of the most likely architecture, island or archipelago, of the polycyclic aromatic hydrocarbon (PAR) core in asphaltenes, molecular orbital (MO) calculations have been carried out considering two PAHs per asphaltene molecule cross-linked (archipelago model) and the same two PAHs aggregated in a parallel fashion and not cross-linked (island model of interacting PAHs). The calculated highest occupied molecular orbital (HOMO) lowest unoccupied molecular orbital (LUMO) gaps (H-L gaps) are compared to the 0-0 band experimental fluorescence emission data of asphaltenes. The calculations of the H-L gap were performed at the semi-empirical ZINDO approach using density functional theory (DFT) dimer-optimized structures (relaxed structures). This methodology was validated against experimental data and it was proven to have a good predictive power. A total of 48 PAHs with 5-10 fused aromatic rings (5FAR-10FAR) were calculated, as well as all of their possible combinations in dimers formed by large core (5FAR-10FAR) large core (SFAR-10FAR) systems (large large core dimers). In total, 1176 systems in the archipelago architecture, crossed linked with a Cs alkane chain, and 1176 systems in the island-stacked interaction were calculated. Also, island and archipelago models were constructed with the 48 PAHs, interacting in both architectures, with 10 PAHs that contain 1-4 fused aromatic rings in the structure (1FAR-4FAR), thus comprising 960 calculations of large core (5FAR-10FAR) small core (IFAR-4FAR) dimers (large small core dimers). Therefore, a total of 3312 systems are calculated in this work. For both cases, large large and large small dimer systems, and for both architectures, island and archipelago, statistical analysis of the results was carried out. It is found that the calculated H-L gap of the dimers with the archipelago architecture is similar to the H L gap of the monomers. For the case of the island dimers (stacked dimers), there is a dependency of the H-L gap upon both the size of the monomers, in terms of the number of fused aromatic rings, and the type of interlayer geometries or stacking arrangement between the monomers composing the island (stacked) dimer. The stacked dimers are more stable in most of the cases than the archipelago dimers. The higher stability in turn produces larger H-L gaps. The remarkably broad variation of the energy gap, of 0.9 eV, between the island and archipelago architectures for the large-large dimers strongly depends upon the dimer size and the stacking arrangement. In the later, the pi-pi interactions play a role but have a minor influence. The stacked island systems that fall inside the experimental range of asphaltenes are, in general, dimers composed with the same monomer in hexagonal (1-1) arrangement and 6FAR-10FAR combinations with parallel displacement (PD) arrangement, mainly without fjords or coves in the structure. Of all of the PAH systems that fall inside the experimental range of asphaltenes when interacting with any other PAH, to form a dimer, in either island or archipelago architecture, the 7FAR PAHs are more abundant in agreement with the former literature. When the percentage of all the calculated dimers, large-large and large-small, is compared, in both architectures, and whose H L gap falls inside the experimental asphaltene fluorescence range, the large large dimers are more abundant than the large small dimers. The large-large dimers are more abundant by 20.6% in island architecture, and by 17.9% in archipelago architecture.It is concluded that indeed, if two asphaltene core PAHs are directly bound via a single bond, then optical methods, such as time-resolved fluorescence depolarization (TRFD) studies, would identify this as a single chromophore, thereby blurring the distinction between island versus archipelago. Some decomposition studies might find this single-bonded pair of PAHs as a single entity as well.