Syntheses, Phase Behavior, Supramolecular Chirality, and Field‐Effect Carrier Mobility of Asymmetrically End‐Capped Mesogenic Oligothiophenes

Abstract

A novel series of asymmetrically end-capped mesogenic oligothiophenes, with various oligothiophene core lengths, alkoxy tail lengths, and molecular polarities through introducing alkylsulfanyl or alkylsulfonyl functionalities as the terminal group, have been synthesized by palladium-catalyzed Suzuki cross-coupling and Kumada cross-coupling reactions as key steps. For the single end-capped oligothiophenes, C(m)O-Ar-OT(4)-H in which m=10, 12, 14, 16, and 18, all of these oligomers exhibited a broad temperature range of highly ordered smectic E and enantiotropic nematic phases, apart from the one with the longest octadecyloxy tail. For the double end-capped series C(10)O-Ar-OT(n)-R, R=Ph-SC(6) or Ph-SO(2)C(6) in which n=1, 2, 3, and 4, oligomers with more than one thiophene ring exhibited smectic A and smectic C phases, various crystal polymorphs and/or unusual low-temperature condensed phases. In the nonpolar, alkylsulfanylphenyl-substituted oligothiophene series, both the crystal/solid melting point and mesogenic clear point increased significantly with an increasing oligothiophene conjugation length. In the polar, alkylsulfonylphenyl-substituted oligothiophene series, all the oligomers showed increased melting points, but decreased mesogenic temperature intervals than those of their corresponding alkylsulfanyl counterparts. Remarkably, two different helical structures showing distinct striated textures or striped patterns were observed with a pitch of several to tens of micrometers under a polarized optical microscope upon cooling from their preceding fluidic smectic phases. The unusual twisted smectic layer structures in the thin solid films exhibiting distinct supramolecular chirality of both handednesses, revealed by circular dichroism measurements, were further confirmed by XRD analyses characterized by a sharp layer reflection together with its higher orders and diffuse wide-angle scatterings. In addition, initial studies showed that the highly ordered smectic phase of the single end-capped oligothiophenes can be utilized to improve field-effect charge mobility. C(10)O-Ar-OT(4)-H showed a hole mobility of 0.07 cm(2) V(-1) s(-1) when deposited on octyltrichlorosilane-treated substrates at 140 degrees C and the on/off current ratios reached 5 x 10(5); on the other hand, its mobility was only 8 x 10(-3) cm(2) V(-1) s(-1) on the same substrate when deposited at room temperature.

Board‐like Fused‐Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self‐Assembly, p‐Type Semiconductivity, and Photoluminescence

“…Fused core terms 7, 5,and 9 (and 11)s elforganize in aC ol hex mesophase, with the mesogensstacked into tilted columns, the cross-section of which is averaged to acylinder.Fused core members 8 and 6 self-organizeinaCol rec mesophase, for which the dumbbellshaped columns of stacked mesogensa re arrangedi narectangular c2mm lattice (Z = 2). The electronic density distributionr esulting from this particular columns hape explains the high intensity difference of fundamental reflections(20)a nd (11). Alongc olumns, the stacking is either tilted (y = 30-408)for 8 or untilted for 6.The mesophase type and the arrangementa re likely the same for 10.The molten chains continuum between the columns is not shownf or clarity.…”

“…The liquid crystalline properties of the final compounds (5)(6)(7)(8)(9)(10)(11) were investigated first by POM (Figure 2a nd Figure S23 in the Supporting Information) and DSC ( Figure S24 in the Supporting Information, DSC data gathered in Table 1). All samples were observed under an opticalp olarizing microscope with a heatings tage, and when slowly cooled from their isotropic liquid states, exhibitedf luid and birefringent optical textures reminiscent of columnar liquid-crystalline phases ( Figure 2): fan-shaped textures typical of columnar textures with strong homeotropic alignment were observed for 5-7 and 9-11.…”

“…Polythiophenes as polymeric semiconductors becomee lectrical conductors when doped: poly(3,4-ethylenedioxythiophene)( PEDOT)d oped with polystyrene sulfuric acid becomes ac onjugated conducting polymer and plays ak ey role in plastic electronics, [5] whereas poly-3-hexylthiophene (P3HT), as ap -type organic semiconductor when paired with the n-type C 60 fullerened erivative, exhibits superiorp erformance in organic photovoltaic solar cells. [6] Oligothiophene derivatives end-capped with alkyl chains, show liquid crystalline properties, [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and prefer to self-organize into supramolecular ordered layered structures:t hey display two-dimensional charge transport mobility comparable to inorganic semiconductors of amorphous and polycrystalline silicon, and have been investigated as active materials in organic field-effect transistors (OFET). [21][22][23][24][25] Discoticl iquid crystals (DLCs) [26][27][28][29] that contain afused-thiophene unit [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] are also ...…”

Room Temperature Multifunctional Organophosphorus Gels and Liquid Crystals

“…These interesting phenomena, along with the ability to trap and immobilize large volumes of solvent and even small molecules, have allowed gels to be implemented in a large array of diverse applications such as drug delivery, tissue engineering, electronics, fluorescent imaging, lithography, sensors, and catalysts, to name just a few 12. Despite the different environmental nature of LCs and gels (viscous solid and colloidal suspension), both of these supramolecular assemblies are known to be the result of a complex balance between non‐covalent attractive forces arising from a rigid scaffold ( π – π stacking, anisotropic dispersion forces, van der Waals interactions and hydrogen bonds), and the disorder introduced by flexible moieties 13…”

Chasing Self‐Assembly of Thioether‐Substituted Flavylium Salts in Solution and Bulk State

“…For H‐bonded, mesomorphic benzoic acids phase transition temperatures of thioether‐substituted derivatives were lower than the alkoxy analogues due to S … S interactions favoring smectic clusters in the nematic phase [7] . Rich polymorphism was observed for asymmetrically end‐capped oligothiophenes upon attachment of thioethers [8] . Upon S/O replacement in the side chains of calamitic imidazolium ILCs, a pronounced decrease of the melting temperatures was detected, while clearing transitions remained constant or even increased, resulting in significantly broadened mesophase ranges [9] .…”