Browsing by Author "Zhang, Haichang"

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Hydrogen-Bonding-Mediated Solid-State Self-Assembled Isoepindolidiones (isoEpi) Crystal for Organic Field-Effect Transistor
(2018-03-22)
Zhang, Haichang
;
Liu, Kewei
;
Wu, Kuan-Yi
;
Chen, Yu-Ming
;
Deng, Ruonan
Novel pigments isoepindolidiones (isoEpi) and di-tert-butyl quinolino[8,7-h]quinoline-1,7-diyl bis(carbonate) (isoEpi-Boc) were synthesized and characterized. The spectroscopic characterizations indicated that the tert-butyloxycarbonyl (t-Boc) units could be removed from soluble isoEpi-Boc by thermal annealing, forming insoluble isoEpi with hydrogen bonding. A solid-state isoEpi-Boc crystal to isoEpi crystal transition was observed during the annealing process and the molecular packing was significantly changed. With the emergence of hydrogen bonds, the isoEpi molecules were arranged into a brick-in-wall structure with pi-stacking along the crystal growth axis, leading to a significant enhancement of charge mobility along the crystal growth direction (the hole mobility from 3.4 x 10(-4) to 0.32 cm(2)/(V.s), and the electron mobility from nondetectable to 5.6 x 10(-3) cm(2)/(V.s)). The results indicate that isoEpi is a promising chromophore for organic field-effect transistor (OFET). The crystal-to-crystal transition driven by the formation of hydrogen bonds is a unique method for modulating the charge transport properties in organic semiconductive materials for OFET devices.
Naphthodipyrrolidone (NDP) based conjugated polymers with high electron mobility and ambipolar transport properties
(2017-06-07)
Zhang, Haichang
;
Zhang, Shuo
;
Mao, Yifan
;
Liu, Kewei
;
Chen, Yu-Ming
Two novel donor-acceptor pi-conjugated polymers based on naphthodipyrrolidone (NDP) were synthesized and characterized. The polymers possess low band gaps and suitable molecular orbital levels as ambipolar semiconductors. The thin film organic field effect transistor of NDP polymers exhibited ambipolar transport properties with a high electron mobility up to 0.67 cm(2) V-1 s(-1). The grazing-incidence wide-angle X-ray scattering (GIWAXS) studies demonstrated that the polymer molecules pack into a long-range-ordered lamellar structure with isotropically oriented crystalline domains. Thermal annealing promoted edge-on lamellar stacking as evidenced by the increased diffraction intensity along the out-of-plane direction. The polymer with NDP and bithiophene units achieved the best edge-on lamellar stacking after thermal annealing, which yielded the best electron transport performance in this work.