第一个烷基链锚定的杂并五苯,二噻吩并[2,3-d;2',3\'-d\']苯并-[1,2-b;3,4-b\']二噻吩(DTmBDT),通过相应的二溴衍生物(Br2-DTmBDT)与硝酰基硝基氧-2-ide金(I)配合物的交叉偶联合成程序,制备了被硝酰基硝基氧基团单取代或二取代。合成的氮氧化物具有高动力学稳定性,这让我们能够研究它们的结构和热量,光学,电化学,和磁性。单自由基和双自由基的单晶X射线衍射表明,硝酰硝基氧基团几乎与最近的噻吩环位于同一平面上。这种排列有利于边缘到边缘二聚体的形成,然后形成由交叉烷基链包围的紧密π堆叠。在融化之前,这些硝酰硝基氧自由基取代的分子经历至少两个不同的相变(PT):对于一元,PT是可逆的,伴随着滞后,并在13和83°C附近发生;加热时的双自由基在2-11°C的温度范围内显示出具有滞后的可逆PT,在135°C附近显示出不可逆的PT。在Br2-DTmBDT中不存在这种类型的PT。因此,硝酰硝基氧逐步取代溴原子会改变DTmBDT的结构组织并诱导PT的出现。这些知识可能有助于π堆叠的顺磁体和相关的分子自旋器件的晶体工程。
The first alkyl chain-anchored heteropentacene, dithieno[2,3-d;2\',3\'-d\']benzo-[1,2-b;3,4-b\']dithiophene (DTmBDT), mono- or disubstituted with a nitronyl nitroxide group has been prepared through a cross-coupling synthetic procedure of the corresponding dibromo-derivative (Br2-DTmBDT) with a nitronyl nitroxide-2-ide gold(I) complex. The synthesized nitroxides possess high kinetic stability, which allowed us to investigate their structure and thermal, optical, electrochemical, and magnetic properties. Single-crystal X-ray diffraction of both mono- and diradicals revealed that the nitronyl nitroxide group lies almost in the same plane as the nearest side thiophene ring. Such arrangement favors formation of edge-to-edge dimers, which then form close π-stacks surrounded by interdigitating alkyl chains. Before melting, these nitronyl nitroxide radical substituted molecules undergo at least two different phase transitions (PTs): for the monoradical, PTs are reversible, accompanied by hysteresis, and occur near 13 and 83 °C; the diradical upon heating shows a reversible PT with hysteresis in the temperature range 2-11 °C and an irreversible PT near 135 °C. PTs of this type are absent in Br2-DTmBDT. Therefore, the step-by-step substitution of bromine atoms by nitronyl nitroxide groups changes the structural organization of DTmBDT and induces the emergence of PTs. This knowledge may facilitate crystal engineering of π-stacked paramagnets and related molecular spin devices.