Side chains in conjugated polymers have been primarily utilized as solubilizing groups. However, these side chains have roles that are far beyond. We advocate using side chain engineering to tune a polymer’s physical properties, including absorption, emission, energy level, molecular packing, and charge transport. To date, numerous flexible substituents suitable for constructing side chains have been reported. In this Perspective article, we advocate that the side chain engineering approach can advance better designs for next-generation conjugated polymers.

Side Chain Engineering in Solution-Processable Conjugated Polymers

Xugang Guo,*,† Antonio Facchetti,*,‡,§ and Tobin J. Marks*,‡ †Department of Materials Science and Engineering, South University of Science and Technology of China, No. 1088, Xueyuan Road, Shenzhen, Guangdong 518055, China ‡Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States

Imide- and Amide-Functionalized Polymer Semiconductors

Charge carrier mobility is still the most challenging issue that should be overcome to realize everyday organic electronics in the near future. In this Communication, we show that introducing smart side-chain engineering to polymer semiconductors can facilitate intermolecular electronic communication. Two new polymers, P-29-DPPDBTE and P-29-DPPDTSE, which consist of a highly conductive diketopyrrolopyrrole backbone and an extended branching-position-adjusted side chain, showed unprecedented record high hole mobility of 12 cm2/(V·s). From photophysical and structural studies, we found that moving the branching position of the side chain away from the backbone of these polymers resulted in increased intermolecular interactions with extremely short π–π stacking distances, without compromising solubility of the polymers. As a result, high hole mobility could be achieved even in devices fabricated using the polymers at room temperature.

Record high hole mobility in polymer semiconductors via side-chain engineering.

Remarkable progress has been made in developing high performance organic field-effect transistors (OFETs) and the mobility of OFETs has been approaching the values of polycrystalline silicon, meeting the requirements of various electronic applications from electronic papers to integrated circuits. In this review, the key points for development of high mobility OFETs are highlighted from aspects of molecular engineering, process engineering and interface engineering. The importance of other factors, such as impurities and testing conditions is also addressed. Finally, the current challenges in this field for practical applications of OFETs are further discussed.

25th anniversary article: key points for high-mobility organic field-effect transistors.

This comprehensive review surveys developments over the past decade in the field of naphthalene diimides (NDIs). It explores their application toward: supramolecular chemistry; sensors; host–guest complexes for molecular switching devices, such as catenanes and rotaxanes; ion-channels by ligand gating; gelators for sensing aromatic systems; catalysis through anion−π interactions; and NDI intercalations with DNA for medicinal applications. We have also explored new designs, synthesis, and progress in the field of core-substituted naphthalene diimides (cNDIs), and their implications in areas such as artificial photosynthesis and solar cell technology. Also presented are some interesting synthetic routes and procedures that can be used toward further development of NDI-bearing compounds for future applications. Finally, we conclude with our views on NDI chemistry for future research endeavors, and we outline what we believe are the key obstacles that need to be overcome for NDIs to see real world applications.

Functional Naphthalene Diimides: Synthesis, Properties, and Applications

Substituted side chains are fundamental units in solution processable organic semiconductors in order to achieve a balance of close intermolecular stacking, high crystallinity, and good compatibility with different wet techniques. Based on four air-stable solution-processed naphthalene diimides fused with 2-(1,3-dithiol-2-ylidene)malononitrile groups (NDI-DTYM2) that bear branched alkyl chains with varied side-chain length and different branching position, we have carried out systematic studies on the relationship between film microstructure and charge transport in their organic thin-film transistors (OTFTs). In particular synchrotron measurements (grazing incidence X-ray diffraction and near-edge X-ray absorption fine structure) are combined with device optimization studies to probe the interplay between molecular structure, molecular packing, and OTFT mobility. It is found that the side-chain length has a moderate influence on thin-film microstructure but leads to only limited changes in OTFT performanc...

Critical Role of Alkyl Chain Branching of Organic Semiconductors in Enabling Solution-Processed N-Channel Organic Thin-Film Transistors with Mobility of up to 3.50 cm2 V–1 s–1

A facile synthesis of 2,3,6,7-tetrabromonaphthalene diimides toward new π-extended naphthalene diimides

Three naphthalene diimides (2, 3 and 4) fused with 2-(1,3-dithiol-2-ylidene)-2-fluorophenylacetonitrile moieties were designed and synthesized. Due to the different substituted positions of fluorine atom on the phenyl group, the solution-processed thin films of 2 and 3 operated in air as n-channel transistors, while the films of 4 performed as ambipolar transistors, indicating that the variation of substituted position of fluorine atom on molecular backbone may tune the material's charge transport behavior.

Tuning the Charge Transport Property of Naphthalene Diimide Derivatives by Changing the Substituted Position of Fluorine Atom on Molecular Backbone

The invention relates to a naphthalimide derivant containing 1, 3-dithiol-2-yliden conjugation units, a preparation method and application thereof. The chemical structure is shown in the specification, wherein when Pi-1 or Pi-2 is groups shown in the specification, R or R is a C1-30 alkyl (of which the formula is shown in the specification), and R is H or alkyls of C1-4; when Pi-1 is equal to Pi-2 and further shown in the specification, the R and the R can not be alkyls at the same time; when the R is equal to the R , both the R and the R are alkyls. All variants of the derivant can be an n-type organic semi-conductor material when the derivant is used to prepare organic thin film transistor devices, and tests show that the electron mobility in the air can reach 0.2cm V s .

Wei Yuan

Papers

Critical Role of Alkyl Chain Branching of Organic Semiconductors in Enabling Solution-Processed N-Channel Organic Thin-Film Transistors with Mobility of up to 3.50 cm2 V–1 s–1

A facile synthesis of 2,3,6,7-tetrabromonaphthalene diimides toward new π-extended naphthalene diimides

Tuning the Charge Transport Property of Naphthalene Diimide Derivatives by Changing the Substituted Position of Fluorine Atom on Molecular Backbone

Naphthalimide derivant containing 1, 3-dithiol-2-yliden conjugation unit, preparation method and application