不同氟取代基对苝酰亚胺电子迁移率的影响

利用空间电荷限制电流(SCLC)法测试了二种氟代苝酰亚胺的电子迁移率, 一种是N,N'-二(五氟代苯基)-3,4,9,10-苝四羧基二酰亚胺(1), 另一种是N,N'-二(1,1-二氢十五氟代辛基)-3,4,9,10-苝四羧基二酰亚胺(2). 结果发现, 化合物2的电子迁移率要比1高1～2个数量级. UV-Vis, XRD, SEM和AFM等表征手段证明, 这一现象可以用不同的氟取代基导致不同的聚集态结构来解释: 对于化合物1而言, 苯环平面与苝环平面之间存在大的夹角, 破坏了苝酰亚胺分子的平面性, 再加上刚性的氟代苯环大的空间位阻作用, 化合物1分子无法依靠相邻苝环之间的重叠排列而结晶, 只能无序堆积形成非晶膜; 与之相反, 在化合物2分子中苝环上的端基是柔性的锯齿状氟代烷基链, 空间位阻小, 化合物2分子能通过相邻苝环之间相互接近而形成的π-π偶合作用而结晶, 因此有利于电子在苝酰亚胺分子间的跳跃传输.

Influences of Different Fluorinated Substituents on Electron Mobility of Perylene Diimides

Electron mobility of two fluorinated perylene diimide compounds was measured by the method of space-charge-limited current: one was N,N'-bisperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide (1), the other was N,N'-bis(1,1-dihydroperfluorooctyl)-3,4,9,10-perylenetetracarboxylic diimide (2). Electron mobility of compound 2 was found to be 1～2 orders of magnitude higher than that of compound 1. Through UV-Vis, XRD, SEM and AFM characterizations, the difference in electron mobility between 1 and 2 can be ascribed to the distinguished aggregate structures originated from different fluorinated substituents: for 1, the angle between the perylene nucleus ring and the perfluorophenyl ring is big, the planarity of perylene diimide molecule is disrupted, the steric hindrance of the rigid fluorinated phenyl ring is large, meaning that compound 1 molecules can not be stacked to crystallize by overlapping of neighboring perylene rings, and as a result, 1 molecules can be stacked randomly to yield an amorphous film, while in contrast, fluorinated terminal substituent of 2 is flexible zigzag alkyl chain with much smaller steric hindrance, so that 2 molecules can form a crystalline film through p-p interactions of successive perylene rings, which will favor electron transport by hopping between molecules.