Synthesis of Methoxy-Substituted Picenes: Substitution Position Effect on Their Electronic and Single-Crystal Structures

A series of picenes having methoxy
groups was synthesized through
Pd-catalyzed Suzuki–Miyaura couplings or Wittig reaction/intramolecular
cyclization sequences, and their physicochemical properties and single-crystal
structures were evaluated. The substitution position effects between
the outer 1,12-, 2,11-, and 4,9-position and the inner 3,10-position
are quite different; the former showed the same electronic structure
as that of picene, but the latter results in a HOMO geometry different
from those of picene and other methoxy picenes. In addition, crystal
structures of four types of methoxy-substituted picenes 4a–c,e strongly depend on their substitution
position and number of methoxy groups, which dramatically changes
the structures from the fully anisotropic 1D π-stacked structure
to a unique 3D herringbone structure due to steric hindrance of methoxy
groups. The calculations of transfer integrals based on their single-crystal
structures reveal that the methoxy picenes have intermolecular overlaps
less effective than that of the parent nonsubstituted picene. These
results are attributed not only to the packing structure but also
to electronic structures such as the HOMO distribution. The preliminary
OFET of the representative 4c,e showed hole
mobilities significantly lower than that of picene due to their less
effective intermolecular overlaps, as predicted by the calculated
transfer integrals.

一系列带有甲氧基的苉（picene）衍生物通过钯催化的铃木偶联（Suzuki–Miyaura）反应或维蒂希（Wittig）反应/分子内环化串联策略合成，并对其理化性质与单晶结构进行了表征。外围1,12位、2,11位与4,9位的取代位置效应与内侧3,10位存在显著差异：前者的电子结构与未取代苉一致，而后者的最高占据分子轨道（HOMO）几何构型与苉及其他甲氧基取代苉均不相同。此外，4种甲氧基取代苉（4a~c、4e）的晶体结构强烈依赖于其取代位置与甲氧基数目；由于甲氧基的空间位阻效应，其堆积结构可从完全各向异性的一维π堆积结构转变为独特的三维鱼骨状结构。基于单晶结构的转移积分计算结果表明，甲氧基取代苉的分子间轨道重叠效果弱于未取代的母体苉。该现象不仅与分子堆积结构有关，同时也受HOMO分布等电子结构因素影响。针对代表性化合物4c与4e的初步有机场效应晶体管（OFET）测试结果显示，其空穴迁移率显著低于苉，这与计算得到的分子间轨道重叠效果较弱的结论一致。