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Abstract π‐conjugated polymers (CPs) that are concurrently soft and stretchable are needed for deformable electronics. Molecular‐level modification of indacenodithiophene (IDT) copolymers, a class of CPs that exhibit high hole mobilities (_hole), is an approach that can help realize intrinsically soft and stretchable CPs. Numerous examples of design strategies to adjust the stretchability of CPs exist, but imparting softness is comparatively less studied. In this study, a systematic molecular weight (MW) series is constructed on a promising candidate for soft CPs, poly(indacenodithiophene‐co‐thienopyrroledione) (p(IDT_C16‐TPD_C8)), by optimizing direct arylation polymerization conditions in hopes of improving stretchability andμ_holewithout significantly impacting softness. We found p(IDT_C16‐TPD_C8) at a degree of polymerization of 32 shows high stretchability (crack onset strain,CoS> 100%) without significantly impacting softness (elastic modulus,E= 32 MPa), which to the best of our knowledge outperforms previously reported stretchable and soft CPs. To further study how molecular‐level modifications impact polymer properties, a MW series of a new extended donor unit polymer, poly(indacenodithienothiophene‐co‐thienopyrroledione) (p(IDTT_C16‐TPD_C8)), was synthesized. The IDTT_C16copolymers did not result in a greater averageμ_holewhen comparing between p(IDTT_C16‐TPD_C8) and p(IDT_C16‐TPD_C8) despite their higher crystallinity observed by GIWAXS. While these findings warrant further investigation, this study points toward unique charge transport properties of IDT‐based polymers. 

Abstract Light‐emitting diodes (LEDs) are a lighting technology with a huge and ascending market. Typically, LED backlights are often paired with inorganic phosphors made from rare‐earth elements (REEs) to tune the emission lineshapes for different applications. However, REE production is a resource‐intensive process with many negative environmental impacts. Herein organic hybrid LEDs are developed using organic dyes synthesized from an abundant and non‐toxic natural product (theobromine) to replace REE phosphors. The resulted hybrid LED generates continuous emission from 400–740 nm, resulting in a high color rendering index (the current industry standard) of 90 and a color fidelity index (the most advanced and comprehensive standard) of 92, challenging commercial LEDs based on REE phosphors. In addition, the light‐converting composite is made from 99 wt% SBS, an inexpensive industrial polymer, and 1 wt% theobromine dyes, reducing the cost of the light converter to ¢1.30 for a 1 W LED, compared to approximately ¢ 19.2 of commercial products. The light converting efficiency of the dye‐SBS composite is 82%. Excited state kinetics experiments are also conducted to provide guidance to further increase the light‐converting efficiency of the theobromine dyes while maintaining excellent color rendering and fidelity. 

Abstract The mechano‐electrical properties of poly(3‐hexylthiophene) thin films are investigated as a function of their tie‐chain content. Tie chains play an indispensable role in enabling strain‐induced structural alignment and charge‐transport enhancement in the strain direction. In the absence of sufficient tie chains, the external mechanical force cannot induce any significant polymer backbone alignment locally or crystallite reorientation at the mesoscale. These samples instead undergo brittle fracture on deformation, with cracks forming normal to the direction of strain; charge transport in this direction is hindered as a consequence. This mechanistic insight on strain alignment points to the promise of leveraging tie‐chain fraction as a practical tuning knob for effecting the mechano‐electrical properties in conjugated polymer systems. 

Abstract This work presents improved compatibility in an elastomer/π‐conjugated polymer blend through side chain functionalization of the electronic polymer. Poly[(3‐(6‐bromohexyl)thiophene)‐ran‐(3‐hexylthiophene)] (P3Br_xHT,x = 0%–100%) was synthesized (i) to improve miscibility with polybutadiene (PB) elastomer through altered π–π interactions and (ii) to covalently bond across phase‐segregated interfaces. Functionalization led to morphology with reduced domain sizes to improve crack onset strain from 7% to 40%. Furthermore, UV‐activated crosslinking reinforced mechanically weak interfaces and yielded at least an additional 40% increase in crack onset strain. Charge mobility in PB/P3Br_xHT organic field‐effect transistors showed minimal dependence on bromide concentration and no negative effects from crosslinking. Functionalization was an effective method to reduce brittleness in PB/P3Br_xHT blends through morphology modification and crosslinking to improve stability towards strain for potential stretchable electronic applications. © 2019 Society of Chemical Industry 

Abstract Research at the University of Washington regarding organic semiconductors is reviewed, covering four major topics: electro‐optics, organic light emitting diodes, organic field‐effect transistors, and organic solar cells. Underlying principles of materials design are demonstrated along with efforts toward unlocking the full potential of organic semiconductors. Finally, opinions on future research directions are presented, with a focus on commercial competency, environmental sustainability, and scalability of organic‐semiconductor‐based devices. 

Abstract Alternating donor–acceptor copolymers are important materials with readily tunable optical and electronic properties. Direct arylation polymerization (DArP) is emerging as an attractive synthetic methodology for the synthesis of these polymers, avoiding the use of prefunctionalized building blocks. However, challenges remain in achieving well‐defined structure, high molecular weight, and impurity‐free polymers. Herein, a study to synthesize three well‐defined donor–acceptor copolymers through DArP is presented. Comparison of¹H NMR and¹³C NMR, as well as optical and electrochemical properties analysis for the polymers and corresponding oligomers provides evidence for the regioregular structure of the polymers. On the basis of the chemical structure of poly(IIDCBT) and the solution electrochemical studies we surmised poly(IIDCBT) could potentially be an electron transport material for organic field‐effect transistors (OFETs), and we determined an electron mobility of 1.2×10⁻³ cm² V⁻¹ s⁻¹for this material. 

Abstract The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F₄TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F₄TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm²V⁻¹s⁻¹in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature.