Rational design of diketopyrrolopyrrole-based oligomers with deep HOMO level and tunable liquid crystal behavior by modulating the sequence and strength of the donor moiety

Abstract

A family of narrow-band gap π-conjugated oligomers and isomers based on diketopyrrolopyrrole and difluorobenzothiadiazole coupled with oligothiophene or thiazole ring have been successfully synthesized. They exhibited intensive absorption bands (300～900 nm) and deep-lying HOMO energy levels (-5.41～-5.60 eV) due to donor-acceptor interaction and multiple fluorine substituents. The sequence and intensity of electron donor moiety play an important role in determining bulk molecular properties, such as the photophysical properties, the HOMO/LUMO energy levels and mesomorphic properties. Compared with isomer DTFB2T, D2TFBT with two n-hexyl-substituted thiophene as the terminal groups exhibited good liquid crystal behavior with Smectic phase when cooled from 180 o C, and it generated a large area of the liquid-crystalline phase at about 100 o C. However, we did not observe such behaviors in DTFB2T due to the different sequence of moiety.We focus our studies on evaluating how structural variations affect molecular properties in two aspects: (1) variation of ability of terminal electron-donor groups through replacing the two thiophenes by two thiazoles to control the molecular energy levels, optical properties; (2) variation of the length (d, J = 3.6 Hz, 1H, Th-H), 8.11-8.10 (d, J = 3.6 Hz, 1H, Th-H), 7.61-7.60 (d, J = 4.8 Hz, 1H, Th-H), 7.28-7.26 (m, 1H, Th-H), 6.95-6.94 (d, J = 3.6 Hz, 1H, Th-H), 2.94-2.90 (t, J = 7.6 Hz, 2H, CH 2 ), 1.81-1.73 (m, 2H, CH 2 ), 1.44-1.32 (m, 6H, CH 2 ), 0.92-0.89 (t, J = 6.8 Hz, 3H, CH 3 ).

Self‐Assembly of Board‐Shaped Diketopyrrolopyrrole and Isoindigo Mesogens into Columnar π‐π Stacks

“…Despite the rapid emergence of diketopyrrolopyrrole (DPP) and isoindigo dyes in the field of organic semiconductors over the last decade,, there are only a handful of reports on small molecule liquid crystals based on DPP and none on isoindigo. These electron deficient dyes are commonly used as acceptor groups in small molecule and polymeric donor‐acceptor structures and known for their excellent luminescent and electronic properties, and high stability ,,,…”

“…Incorporation of DPP and isoindigo into liquid crystalline structures has been hampered by limited options for substitution and their high propensity for crystallization ,. Their molecular shapes and positions for substitution naturally lead to overall rod‐shaped structures that may self‐assemble into lamellar arrangements (smectic phases) . While some higher ordered smectic mesophases have been shown to be reasonable organic semiconductors,, self‐assembled columnar π‐π stacks more reliably generate diverse charge conducting organic materials ,…”

“…[1][2][3] Which supramolecular structures are generated is usually controlled by molecular design as the self-assembly of molecules is guided by shape anisotropy, π-π stacking, electrostatic interactions, and microphase segregation between incompatible groups. [4][5][6][7][8] Despite the rapid emergence of diketopyrrolopyrrole (DPP) and isoindigo dyes in the field of organic semiconductors over the last decade, [9,10] there are only a handful of reports on small molecule liquid crystals based on DPP [11][12][13][14] and none on isoindigo. These electron deficient dyes are commonly used as acceptor groups in small molecule and polymeric donor-acceptor structures and known for their excellent luminescent and electronic properties, and high stability.…”

“…[17,18] Their molecular shapes and positions for substitution naturally lead to overall rod-shaped structures that may self-assemble into lamellar arrangements (smectic phases). [11][12][13] While some higher ordered smectic mesophases have been shown to be reasonable organic semiconductors, [19,20] self-assembled columnar π-π stacks more reliably generate diverse charge conducting organic materials. [4,19] The complexity of converting DPP and isoindigo into π-π stacking columnar liquid crystals is illustrated by the lack of reports.…”

Columnar Mesomorphism of Board‐Shaped Perylene, Diketopyrrolopyrrole, Isoindigo, Indigo, and Quinoxalino‐Phenanthrophenazine Dyes

“…[148] Derivatives DPP-18 a-b in Figure 23 rather display soft crystal mesophases than liquid crystal phases based on the provided DSC data and POM images. [149,150] DPP derivatives have been used as components of liquid crystalline polymers [151,152] and as dye additives to liquid crystal matrices [153,154] that are not further discussed here. Also outside the scope of this review are DPP derivatives that self-assemble on surfaces and at interfaces [155,156] or show specific types of aggregation.…”