二聚化小分子受体（DSMA）因其在有机太阳能电池（OSC）领域展现出的长期的形貌稳定性和优异的重复性而备受关注。然而，基于DSMA的OSC的功率转换效率高度依赖于二聚化模式，且其基本的结构-性能关系仍不清楚。
近日，中国科学院化学研究所易院平研究员和韩广超副研究员等人在Science China Materials发表研究论文，利用多尺度理论计算揭示了A-D-A小分子受体（SMA）的末端基团（EG）工程在调节以乙烯基为桥的DSMAs的电子、光学和载流子传输特性中的作用。
本文要点
1) 结果表明，EG工程可以有效调节SMA的最低未占据分子轨道（LUMO）在连接原子上的电子密度，从而显著改变DSMA中两个SMA单元间的超交换（SE）电子耦合以促进分子内电子转移。因此，相应的DSMA的LUMO能量及其分布也会发生显著变化，进一步影响其激发态能量和振子强度。2) 不同的EG对分子间电子耦合和电子连接性也有重要影响。3) 与报道的名为BB-V的DSMA相比，新设计的NB-V由于相对平衡的分子内和分子间电子耦合，在光吸收和电子迁移率方面同时获得提升。本工作为发展DSMA、提高OSC性能提供了有益的见解。Figure 1. Chemical structures (R1 = 2-octyldodecyl; R2 = nonyl) and intramolecular super-exchange electronic couplings of the studied DSMAs. The dihedral angle between the SMA end-group and vinyl bridge is illustrated in magenta.Figure 2. (a) Energy levels of the HOMO and LUMO as well as the HOMO-LUMO gap. (b) Pictorial representation of the LUMOs for the studied DSMAs.Figure 3. (a) Distributions of the dihedral angle θ for the DSMAs in the simulated films. (b) Average number of π-π packing dimers for each DSMA molecule in the simulated films. The molecular pair with ≥8 interacting atoms (inter-atomic distance smaller than the sum of their atomic van der Waals radii) is regarded as a π-π packing dimer. (c–f) Distribution proportions of interacting pairs for BB-V (c), NN-V (d), NB-V (e), and NT-V (f) in the simulated films.![]()
Figure 4. Distributions of the intramolecular super-exchange coupling Veff (a) and the intermolecular direct coupling Vdrt between the π-π stacking SMA units (c) for BB-V, NN-V, and NB-V in the simulated films. The total numbers of π-π stacking per SMA unit are indicated in brackets. Average number of neighbors for each SMA unit (b) and proportion of the number of SMA units for the largest connection network (d), as a function of the threshold coupling VT. (e) Illustration of the largest connection network for BB-V, NN-V, and NB-V with VT of 10 meV. The green balls denote the center-of-mass of the SMA units; the red and blue lines represent the connections via intramolecular and intermolecular couplings, respectively.Yaogang Zhang, Guangchao Han, Yuanping Yi. Electronic, optical, and charge transport properties of dimerized small-molecule acceptors: the role of end-group engineering. Sci. China Mater. (2024).https://doi.org/10.1007/s40843-024-3183-6
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