@article {48087, title = {Instabilities as the origin of large-area self-assembled and aligned organic semiconductor nanocrystals}, journal = {ACS Applied Electronic Materials}, volume = {4}, year = {2022}, month = {APR}, pages = {1815-1822}, type = {Article}, abstract = {

Aligned nanocrystals of organic semiconductors (OSCs) are highly desirable for electronic devices and biomedical and photonic applications. Solution-based wet processing routes have the potential to produce aligned nanocrystals over large areas in small time frames. Herein, we demonstrate that by optimizing the hydrodynamic evaporative processes, controlled long-range crystalline assemblies of OSCs can be achieved (longest nanocrystal similar to 3 mm) purely through physical processes: namely, from fingering instabilities. Self-assembly is achieved here without strong noncovalent interactions such as hydrogen-bonding interactions. Experimentally our approach involves just placing a drop of a solution on an inclined substrate. Nanocrystals with widths of 300-800 nm and lengths of millimeters (length/width aspect ratios \>10(5)) are formed in less than 2-8 s. A hydrazine chemiresistive sensor based on the aligned crystalline patterns show unprecedented responsivity (similar to 10(-6)), 2 orders greater than those of stick-slip patterns. Finally, experimental parameters that need optimization to achieve nanocrystal patterns are investigated in detail and pointers to fabricate such OSC nanocrystals are provided.

}, keywords = {aligned fibers, diketopyrrolopyrrole, fingering instability, nanocrystal arrays, naphthalenediimide, organic semiconductors}, doi = {10.1021/acsaelm.2c00061}, author = {Venugopalan, Vijay and Jain, Bhanprakash and Mahale, Rajashree Y. and Subramani, Kumar and Krishnamoorthy, Kothandam} } @article {49402, title = {Variations in packing as a function of side chains in random copolymers and its impact on charge carrier mobility}, journal = {Macromolecular Chemistry and Physics}, year = {2024}, month = {OCT }, type = {Article; Early Access}, abstract = {

Homopolymers and alternating copolymers of conjugated molecules exhibit impressive performance in electronic devices. Despite the well-established procedures, the synthesis of alternating copolymers using three monomers is not as easy as random copolymers. Besides facile synthesis, the random copolymers can match the performance of alternating copolymers in electronic devices. Herein, random copolymers are designed and synthesized comprising thienoisoindigo (TIIG), diketopyrrolopyrrole (DPP), and thiophene. The DPP monomers installed with various side chains including branched alkyl chain, branched alkyl chain with ester functionality, linear oligo ethylene glycol, and siloxane terminated alkyl chain are incorporated into the polymers (P1, P2, P3, and P4, respectively). All the thermally stable, low bandgap random copolymers exhibited strong H-type aggregation in thin film. The relationship between thin film microstructure originating from diverse side chains and the charge transport in organic field effect transistors (OFETs) is investigated. All the random copolymers exhibited predominantly p-type charge transport and a maximum hole mobility of 2 x 10-2 cm2 V-1s-1 is observed for P3. The packing of all the polymers is examined theoretically by density functional theory (DFT) and compared with experimental values obtained from grazing incident X-ray diffraction (GIXRD). Various side chains (hydrophilic and hydrophobic) affect molecular packing of random polymers which ultimately affects its thin film morphology and semiconducting performances. Linear chains provide better interchain packing by pi-pi stacking compared to bulky branched side chains. The incorporation of heteroatoms and polar groups into the side chain further enhances the interchain interactions. image

}, keywords = {diketopyrrolopyrrole, organic field effect transistor, random polymer, side chain engineering, thienoisoindigo}, issn = {1022-1352}, doi = {10.1002/macp.202400294}, author = {Swain, Gitanjali and Kumar, Subramani and Samudre, Nikhil S.} } @article {49676, title = {Long cycling stability imparted to li-ion batteries by conjugated polymers with low dihedral angles and high electron density on functional groups}, journal = {ACS Applied Polymer Materials}, volume = {7}, year = {2025}, month = {JUN}, pages = {7719-7728}, type = {Article}, abstract = {

In conjugated polymers, dihedral angles at bonds connecting their monomers impact the polymers{\textquoteright} properties such as the packing of the polymer chains, bandgap, and conductivity. These properties are expected to impact the performance of rechargeable Li-ion batteries because the Li-ion transport and conductivity of the polymers are two important parameters. To understand this, we designed and synthesized two polymers with two different dihedral angles. The polymer, Poly(EDOT-DPP), comprising diketopyrrolopyrrole (DPP) and ethylenedioxythiophene (EDOT) as monomers, showed a low dihedral angle of 2 degrees. On the other hand, the polymer, Poly(EDOT-i-Ind), comprising EDOT and i-Indigo (i-Ind) showed a dihedral angle of 17 degrees. Density functional theory (DFT) studies showed that the electron density at the carbonyl moiety of EDOT-DPP is higher than that of EDOT-i-Ind. This resulted in a higher Li+ binding energy of -3.665 eV for EDOT-DPP and a lower Li+ binding energy of -3.464 eV for EDOT-i-Ind. Battery electrodes were fabricated using either Poly(EDOT-DPP) or Poly(EDOT-i-Ind) with multiwalled carbon nanotubes as conducting fillers in the absence of any binders. The Li+ ion diffusion coefficient ( D Li + ) measured for the as prepared batteries based on Poly(EDOT-DPP) was found to be 3.9 x 10-19 cm2/s, which is slightly higher than that found for Poly(EDOT-i-Ind). However, after 2000 cycles, the D Li + increased by about two orders of magnitude for both polymers. Due to the low dihedral angle in the case of Poly(EDOT-DPP), the D Li + was found to be 21\% higher than that of Poly(EDOT-i-Ind). The higher binding of Li+ ions with Poly(EDOT-DPP) and Li+ ion diffusion improved the specific capacity and cycling performance of batteries fabricated with this polymer. At a current density of 0.2 A/g, Poly(EDOT-DPP) showed a 39\% higher specific capacity than the Poly(EDOT-i-Ind) polymer after 2000 cycles. The batteries also showed stable performance over 2000 cycles with an insignificant decrease in specific capacity.

}, keywords = {dihedral angle, diketopyrrolopyrrole, i-indigo, Li-ion battery, Li-ion transport}, issn = {2637-6105}, doi = {10.1021/acsapm.4c04072}, author = {Kargude, Radhakisan and Srinivasalu, Hari Haran and Devasia, George and Krishnamurty, Sailaja and Krishnamoorthy, Kothandam} }