End-Capping π-Conjugated Naphthodithiophene Diimide (NDTI)-Based Triads with Noncovalent Intramolecular S···O Interactions: A Route towards High-Performance Solution-Processable Air-Stable n-Type Semiconductors

Abstract

Introducing noncovalent intramolecular interactions into functional π-conjugated organic molecules or polymers is a useful method to improve the performance of organic semiconducting devices. In this study, two small molecules based on naphthodithiophene diimide (NDTI), NDTI-BTIC1 and NDTI-BTIC2, were successfully designed and synthesized by covalently connecting an electron-deficient NDTI-core and two 3-(dicyanomethylidene)-indan-1-one (IC) groups with thiophene substituted by an alkoxy chain or alkyl chain, respectively. Density functional theory (DFT) calculations on the optimized geometries of the triads predict that the existence of noncovalent intramolecular S (thiophene)···O (alkoxy) interactions is possible in NDTI-BTIC1. The molecular orbital distributions of NDTI-BTIC1 and NDTI-BTIC2 show that the lowest unoccupied molecular orbitals (LUMOs) are delocalized in the whole molecule, implying the possibility to show n-type transport characteristics. The two molecules further demonstrated LUMOs at a low altitude of −4.37 to −4.45 eV, low enough for the stable transmission of electrons in the atmosphere. The solution-processing method was used to prepare transistors based on the two molecules’ bottom-gate top-contact (BGTC), which exhibited unipolar n-type field-effect transistor (FET) characteristics in the air. The FET performance of NDTI-BTIC1 is higher than that of NDTI-BTIC2 in both the as-spun and thermal annealed films, possibly attributed to the existence of noncovalent intramolecular S···O interactions in NDTI-BTIC1. Moreover, the maximum electron mobility of NDTI-BTIC1 obtained at 150 °C thermal annealing is improved by one order of magnitude compared to that of NDTI-BTIC2, being 0.17 and 0.085 cm2 V–1 s–1, respectively. The transport difference of the two molecules was proved by film morphology analysis. The results show that constructing noncovalent intramolecular S···O conformational locks between the TIC unit and NDTI can improve the organic field-effect transistor (OFET) devices’ performance through reasonable molecular design strategies.

Non-covalent interactions (NCIs) in π-conjugated functional materials: advances and perspectives

“…n-Type OFET with lowered LUMO level to reduce electron injection barrier and effectively improve electron injection is indeed in high demand. Hu and co-workers 99 developed π-conjugated backbones 48a and 48b (Chart 6) with low LUMO energy levels (HOMO/LUMO = −4.37/−5.93 vs. −4.45/−6.15 eV). OFET devices with a bottom-gate-top-contact (BGTC) configuration under atmospheric conditions show that both molecules exhibited unipolar n-channel OFET performance (Table 3).…”

Molecular Design Concept for Enhancement Charge Carrier Mobility in OFETs: A Review

“…The result indicates that the µ h of CTZ is only 0.076 cm 2 V −1 s −1 , while the value of PCTZ-T is almost 30 times increased, which is up to 1.98 cm 2 V −1 s −1 . Ran et al [61] introduced the S. . .…”

Enhanced Solvent and Thermal Stability in Cross‐Linkable Conjugated Statistical Copolymers for Organic Field‐Effect Transistors

“…), film-deposition processing (bar coating, [16] dip coating, [17] solution shearing, [18,19] etc. ), and post-processing (thermal annealing, [20] solvent annealing, [21] mechanical stretching, [22] rubbing, [23] etc.). Solvent and thermal annealing have been proved to be efficient to improve the ordering of solid-state packing in conjugated polymers.…”