Tuning charge transport from unipolar (n-type) to ambipolar in bis(naphthalene diimide) derivatives by introducing π-conjugated heterocyclic bridging moieties

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2016-01, Vol.4 (3), p.723-724
• Main Authors: Wang, Zongrui, Li, Xiangguang, Zou, Ye, Tan, Jiahui, Fu, Xiaolong, Liu, Jie, Xiao, Chengyi, Dong, Huanli, Jiang, Wei, Liu, Feng, Zhen, Yonggang, Wang, Zhaohui, Russell, Thomas P, Hu, Wenping
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Diimide; Electronics; Energy gaps (solid state); Field effect transistors; Molecular orbitals; Semiconductor devices; Semiconductors
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c6tc01769j

A series of acceptor-donor-acceptor (A-D-A) conjugated molecules based on naphthalene diimide dimers bridged with different π-conjugated heterocyclic units (NDI-π-NDI) have been designed and synthesized. By an ingenious design strategy, the LUMO (the lowest unoccupied molecular orbital) of the NDI-based small molecules is well controlled to a relatively constant value of −3.8 to −3.9 eV, whereas their HOMO (the highest occupied molecular orbital) could be tuned over a wide range, from −6.5 eV (compound 1 ) to −5.5 eV (compound 5 ), leading to varied band gaps from 2.6 eV to 1.5 eV. Organic field-effect transistor (OFET) characterization of these NDI-π-NDI molecules shows that compounds 1 , 2 , and 3 have good n-type semiconducting properties in a N 2 atmosphere with the maximum electron mobilities up to 0.15 cm 2 V −1 s −1 , 0.46 cm 2 V −1 s −1 and 0.57 cm 2 V −1 s −1 , respectively. Compounds 4 and 5 , due to the high-lying HOMO levels and reduced energy band gaps, have ambipolar semiconducting properties and OFETs based on 5 show the highest electron and hole mobilities up to 1.23 cm 2 V −1 s −1 and 0.0074 cm 2 V −1 s −1 , respectively. Moreover, the performances are enhanced under thermal treatment because of the increased crystallinity as evidenced by X-ray diffraction (XRD) and atomic force microscopy (AFM). The easily tunable electronic energy levels make the NDI-based semiconductors promising n-channel and ambipolar components in organic devices. The charge transport polarity of a series of acceptor-donor-acceptor (A-D-A) conjugated molecules can be tuned from unipolar (n-type) to ambipolar.