Materials Design via Optimized Intramolecular Noncovalent Interactions for High-Performance Organic Semiconductors

Abstract

We report the design, synthesis, and implemention in semiconducting polymers of a novel head-to-head linkage containing the TRTOR (3-alkyl-3′-alkoxy-2,2′-bithiophene) donor subunit having a single strategically optimized, planarizing noncovalent S•••O interaction. Diverse complementary thermal, optical, electrochemical, X-ray scattering, electrical, photovoltaic, and electron microscopic characterization techniques are applied to establish structure−property correlations in a TRTOR-based polymer series. In comparison to monomers having double S•••O interactions, replacing one alkoxy substituent with a less electron-donating alkyl one yields TRTOR-based polymers with significantly depressed (0.2−0.3 eV) HOMOs. Furthermore, the weaker single S•••O interaction and greater TRTOR steric encumberance enhances materials processability without sacrificing backbone planarity. From another perspective, TRTOR has comparable electronic properties to ring-fused 5Hdithieno[3,2-b:2′,3′-d]pyran (DTP) subunits, but a centrosymmetric geometry which promotes a more compact and ordered structure than bulkier, axisymmetric DTP. Compared to monosubstituted TTOR (3-alkoxy-2,2′-bithiophene), alkylation at the TRTOR bithiophene 3-position enhances conjugation and polymer crystallinity with contracted π−π stacking. Grazing incidence wide-angle X-ray scattering (GIWAXS) data reveal that the greater steric hindrance and the weaker single S•••O interaction are not detrimental to close packing and high crystallinity. As a proof of materials design, copolymerizing TRTOR with phthalimides yields copolymers with promising thin-film transistor mobility as high as 0.42 cm 2 /(V•s) and 6.3% power conversion efficiency in polymer solar cells, the highest of any phthalimide copolymers reported to date. The depressed TRTOR HOMOs imbue these polymers with substantially increased I on /I off ratios and V oc 's versus analogous subunits with multiple electron donating, planarizing alkoxy substituents. Implementing a head-to-head linkage with an alkyl/alkoxy substitution pattern and a single S•••O interaction is a promising strategy for organic electronics materials design.

Head‐to‐Head Linkage Containing Bithiophene‐Based Polymeric Semiconductors for Highly Efficient Polymer Solar Cells

“…Among various nTs, terthiophene (3T) and tetrathiophene (4T) are highly promising ones . In order to improve solubilizing capability of 2T and achieve a high degree of coplanarity, we design a novel donor unit, the head‐to‐head linkage containing 3‐alkoxy‐3′‐alkyl‐2,2′‐bithiophene (TRTOR) . The TRTOR contains two solubilizing chains and has a high degree of coplanarity enabled by intramolecular sulfur–oxygen interaction .…”

Donor–acceptor photovoltaic polymers based on 1,4‐dithienyl‐2,5‐dialkoxybenzene with intramolecular noncovalent interactions

“…In an alternative approach, intramolecular non‐covalent interactions can be adopted to induce conformation lock and backbone planarization. For example, non‐covalent S…O coulomb attraction has been found between the sulfur of thienyl unit and the oxygen of alkoxyl or carbonyl substituents on adjacent aromatics, and was utilized in the design of a variety of conjugated polymers and small molecular semiconductors . Most of the works demonstrated that such non‐covalent S…O interactions can improve the material performance and achieve a PCE over 9.39% and mobility higher than 5.37 cm 2 V −1 s −1 .…”

Theory Meets Experiment for Noncovalent Complexes: The Puzzling Case of Pnicogen Interactions

“…Noncovalent interactions play ak ey role in several biological [1] and technological processes, [2][3][4][5] yet their characterization and interpretation are still far from being satisfactory,especially when the bonding pair is made up of two nonhydrogen atoms.I nt his connection, integrated experimental and computational investigations can play an invaluable role provided that the accuracy of the results is accompanied by their rigorous and understandable interpretation. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C À H···O and CÀH···N hydrogen bonds.F urthermore,aSAPT analysis shows that electrostatic and dispersion interactions play ac omparable role in stabilizing the complex.…”

“…Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C À H···O and CÀH···N hydrogen bonds.F urthermore,aSAPT analysis shows that electrostatic and dispersion interactions play ac omparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination.Noncovalent interactions play ak ey role in several biological [1] and technological processes, [2][3][4][5] yet their characterization and interpretation are still far from being satisfactory,especially when the bonding pair is made up of two nonhydrogen atoms.I nt his connection, integrated experimental and computational investigations can play an invaluable role provided that the accuracy of the results is accompanied by their rigorous and understandable interpretation. Along with the well-established hydrogen and halogen bonds,e merging classes of noncovalent interactions are attracting increasing attention, such as the R À X···Y ones involving apnicogen atom (X = N, P, As,SborBi), [6] with RÀXand Ybeing the pnicogen bond donor and acceptor,r espectively,i na nalogy with hydrogen [7] and halogen bond definitions.…”