Photoresponsive organic field-effect transistors involving photochromic molecules

In recent years,organic field-effect transistors（OFETs） with high performance and novel multifunctionalities have attracted considerable attention.Meanwhile,featured with reversible photoisomerization and the corresponding variation in color,chemical/physical properties,photochromic molecules have been applied in sensors,photo-switches and memories.Incorporation of photochromic molecules to blend in the device functional layers or to modify the interfaces of OFETs is common way to build photo-transistors.In this review,we focus on the recent advantages on the study of photoresponsive transistors involving one of three typical photochromic compounds spiropyran,diarylethene and azobenzene.Three main strategies are demonstrated in detail.Firstly,photochromic molecules are doped in active layers or combined with semiconductor structure thus forming photoreversible active layers.Secondly,the modification of dielectric layer/active layer interface is mainly carried out by bilayer dielectric.Thirdly,the photo-isomerization of self-assembled monolayer（SAM） on the electrode/active layer interface can reversibly modulate the work functions and charge injection barrier,result in bifunctional OFETs.All in all,the combination of photochromic molecules and OFETs is an efficient way for the fabrication of organic photoelectric devices.Photoresponsive transistors consisted of photochromic molecules are potential candidate for real applications in the future.

Benzobisthiazole Polymer with Resonance-assisted Hydrogen Bonds for High-performance Transistor and Solar Cell Applications

Benzobisthiazole polymer with resonance-assisted hydrogen bonds(RAHBs)has been synthesized for both organic field-effect transistor and polymer solar cell applications.The properties of the hydrogen bonded polymer are compared with the reference polymer without RAHBs.Single-crystal X-ray diffraction analyses of the building block reveal that the RAHB interactions are formed between the carbamate hydrogen and imine nitrogen of the thiazoles.The hydrogen donor and acceptor are connected byπ-conjugated molecular framework and the hydrogen-bridged quasi aromatic rings lock the conformation of the building block.The building block adopted a layered sandwich packing in crystal instead of slipped herringbone stacking which was often found in the crystal of benzobisthiazole derivatives.The polymer PCBTZ-TT with RAHBs showed deeper HOMO/LUMO energy level(about 0.2 eV)than reference polymer.The PCBTZ-TT demonstrated the hole mobility of0.96 cm^(2)·V^(-1)·s^(-1) in field-effect transistor devices and achieved power conversion efficiency of 13.6%in solar cell devices with Y6 as acceptor without any additive.

Fine-tuning the molecular energy levels by incorporating thiophene units onto the π-backbone of core-expanded naphthalene diimides

A series of core-expanded naphthalene diimides（NDI-DTYM） and thiophene-based derivatives（1a-c）were designed and synthesized to investigate the relationship between molecular structures and the highest occupied molecular orbital（HOMO） energy levels but has little impact on the lowest unoccupied molecular orbital（LUMO） energy levels.The results demonstrated that increasing the number of thiophene units can gradually elevate the HOMO energy levels but had little impact on the LUMO energy levels.The n-channel organic field-effect transistors（OFETs） based on 1b and 1c have demonstrated that these almost unchanged LUMO energy levels are proper to transport electrons.

The role of halogen bonding in improving OFET performance of a naphthalenediimide derivative

Controlling microstructure and thin film morphology of organic semiconductors by supramolecular arrangement is critical to improving their device performance. To realize well-controlling supramolecular assembly, a core-expanded naphthalene diimides derivative （1） was designed and synthesized as an n-type organic semiconductor and also as a halogen bonding （XB） donor that could form complementary XBs with 2,2-dipyridine or 2,2-bipyrimidine acceptor. The XB interactions in the solid state of 1/2,2- dipyridine and 1/2,2-bipyrimidine were confirmed by a series of characterization methods, such as thermal gravimetric analysis （TGA）, X-ray photoelectron spectroscopy （XPS）, nuclear magnetic resonance （NMR） involving 13F NMR and solid-state 13C NMR. Organic field-effect transistors （OFETs） based on XB complexes 1/2,2-dipyridine or 1/2,2-bipyrimidine showed better device performance than that of devices based on pure 1, with the average electron mobility increased more than doubled （from 0.027cm2V-1 s-1 to 0.070cm2V-1 s-1）.

Photoresponsive n-channel organic field-effect transistors based on a tri-component active layer

Introducing photochromic molecules into the active layer of organic field-effect transistors （OFETs） is a direct way to implement a photoresponse nature in OFETs. However, active layer blended photo- responsive transistors based on n-type semiconductors are challenging and rarely studied, which are crucial for multifunctional organic-based logic applications. Herein, we fabricated n-channel photo- responsive OFETs based on a tri-component active layer spin-coated from the mixed solution of an n-type semiconductor （NDI2OD-DTYM2）, spiropyran and polystyrene with a weight ratio of 1：1：1. The morphology of the blended films was improved by the introduction of the polymer matrix. Photochromic spiropyran molecules dispersed in the semiconductor layer could switch between the closed-ring state and ionic open-ring state flexibly under the irradiation of different wavelengths of light, and thus change the channel conductivity reversibly and modulate the OFET characteristics. Therefore, under the irradiation of alternate UV and vis light, both the device carrier mobility and current on and off ratio successfully realized a reversible switch.

Introduction to the Special Issue of π-Functional Molecules ＆ Polymers

π-Functional materials refer to small molecules and polymers that contain conjugated structures and exhibit interesting electronic and optical properties and may have potential applications.Early applicationsπ-conjugated organic systems can be dated back to eighteen century when organic molecules containing aromatic unites were used as dyes and pigments.