Browsing by Author "Kumar, Sushil"

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Accessing pi-expanded heterocyclics beyond dibenzothiophene: Syntheses and properties of phenanthrothiophenes
(1970-01-01)
Venkateswarlu, Samala
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Prakoso, Suhendro Purbo
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Kumar, Sushil
;
Tao, Yu-Tai
;
應用化學系
A series of phenanthrothiophenes are designed and synthesized from polyarylthiophenes through regioselective Scholl reactions in one step using iron chloride as catalyst. The molecular structures of these heteroarenes displayed multiple twisted fjords, which perturb the shapes of the polycyclic frameworks to pack in slipped to near-perfect face-to-face styles in parallel or antiparallel packings. Field-effect transistor devices using single crystals of 6,12-difluorodiphenanthro[9, 10-b:9 ', 10 ']thiophene gave a hole mobility of 0.22 cm(2) V-1 s(-1).
Benzophenanthrothiophenes: Syntheses, Crystal Structures, and Properties
(2019-09-06)
Venkateswarlu, Samala
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Prakoso, Suhendro Purbo
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Kumar, Sushil
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Kuo, Ming-Yu
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Tao, Yu-Tai
A new class of polycyclic heteroarenes based on benzo[3,4]phenanthro[1,2-b]benzo[3,4]phenanthro[2,1-d]thiophene (BPBPT) was prepared from polyaryl thiophenes via regioselective Scholl reactions. The molecular frameworks of these compounds exhibited twisted bridges and near-cofacial packing motifs with oppositely or parallel pi-stacked structures depending on the substituents on the periphery. Theoretical calculation of electronic coupling and charge mobility was carried out on the basis of the single-crystal structures. Single crystals of selected benzophenanthrothiophenes were used in p-channel field-effect transistor device fabrication, from which the highest mobility was measured as 2.03 cm(2) V-1 s(-1) from Flu-BPBPT.
n-Type Thin-Film Transistors Based on Diketopyrrolopyrrole Derivatives: Role of Siloxane Side Chains and Electron-Withdrawing Substituents
(2020-01-08)
Prakoso, Suhendro Purbo
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Kumar, Sushil
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Wu, San-Lien
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Ciou, Guan-Ting
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Ke, Yao-Jin
The physical properties, packing, morphology, and semiconducting performance of a planar pi-conjugated system can be effectively modified by introducing side chains and substituent groups, both of which can be complementary to the pi framework in changing the intermolecular association, frontier molecular orbital energy, optical band gap, and others. We herein show that installation of end-capped electron-withdrawing groups (EWGs), such as dicyanovinyl (-DCV), 3-ethylrhodanine (-RD), and 2-(3-oxo-indan-1-ylidene)-malononitrile (-INCN), together with siloxane side chains to the backbones of dithienyldiketopyrrolopyrrole (DPPT), such as DPPT-Si-DCV, DPPT-Si-RD, and DPPT-Si-INCN, can greatly improve its solubility, air stability, and film morphology to serve as an n-channel in thin-film transistor fabrication. The EWGs attached to the DPPT core narrowed the optical band gap (E-g(opt)) and changed the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies (E-HOMO and E-LUMO), making them suitable for n-channel field-effect transistor (FET) applications. The benefits of introducing siloxane side chains to the DPPT core include enhanced solubility, low crystallization barrier, enantiotropic phase behavior, and much improved FET performance. The DPPT-Si-INCN film displayed low-lying HOMO (-5.82 eV) and LUMO (-4.60 eV) energy levels and an optical band gap as low as 1.22 eV, all of which suggest that this derivative can be quite resistant toward aerial oxidation. Thin films of these derivatives were prepared by the solution-shear method. A comparison of the solution-sheared films indicated that the molecular packing motif of DPPT-Si-INCN film was somehow different from that of DPPT-Si-DCV and DPPT-Si-RD, in which the pi-pi stacking tended to align orthogonally to the shearing direction. This specific pi-pi stacking alignment could have an impact on the electron mobility (mu(e)) values in transistors based on the solution-sheared films.
Nonlinear Polyfused Aromatics with Extended pi-Conjugation from Phenanthrotriphenylene, Tetracene, and Pentacene: Syntheses, Crystal Packings, and Properties
(2018-10-05)
Kumar, Sushil
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Huang, Ding-Chi
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Venkateswarlu, Samala
;
Tao, Yu-Tai
;
應用化學系
New classes of nonlinear polyaromatics with extended conjugation at lateral and longitudinal directions from triphenylene, tetracene, and pentacene backbones are reported. These planar and twisted polyfused aromatics are obtained through specific and selective multifold Scholl reactions from predesigned polyaryls. These derivatives displayed shifted or perfect cofacial packing motifs. Single crystals of one derivative, phenanthro[9,10:b]triphenylene, were used as p-channel materials in fabricating transistor devices, which exhibited an average mobility of 0.38 cm(2) s(-1) and a maximum mobility reaching 1.15 cm(2) V-1 s(-1)
Polysubstituted Hexa-cata-hexabenzocoronenes: Syntheses, Characterization, and Their Potential as Semiconducting Materials in Transistor Applications
(2019-07-05)
Kumar, Sushil
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Pola, Someshwar
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Huang, Chih-Wei
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Islam, Md. Minarul
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Venkateswarlu, Samala
A series of tetra- and octa-substituted hexa-cata-hexabenzocoronenes (cata-HBCs) were synthesized from tetraryl olefins via iodine- and iron chloride-catalyzed oxidative cyclodehydrogenation reactions. The substitutions on the periphery of the parent HBC serve to modify the photophysical properties, highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, and thermal stabilities of the respective derivatives. The crystal structures were determined to display multiple twists in the framework, resulting in different packing motifs depending on the position, type, and number of functional groups on the hexabenzocoronene framework. Nearly perfect co-facial packing to marginally or extensively shifted co-facial stacks were obtained due to substitution. The single crystals of parent HBC were used to fabricate single-crystal field-effect transistors, from which the highest p-channel mobility of 0.51 cm(2) V-1 s(-1) was measured. Thin-film transistors of selected HBCs were also prepared, and 0.61 cm(2) V-1 s(-1) was obtained for MeHBC-2. These results attest the potential of these materials as semiconducting materials.