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This study reports two novel n-channel pyromellitic diimide (PyDI) derivatives, PyDI-BOCF3 and PyDI-BSCF3, with particularly wide energy gaps of 3.56 eV and 3.49 eV in the solid state, respectively, which induce the investigations of their charge transport properties, photostabilities and thin-film transparency of organic field-effect transistors (OFETs) in this work. Although PyDI-BOCF3 and PyDI-BSCF3 exhibit similar two-dimensional (2D) lamellar packing motifs, PyDI-BSCF3 demonstrates stronger electronic couplings than those of PyDI-BSCF3, suggesting it may show better electrical performance in OFETs. As predicted, PyDI-BSCF3 shows an electron mobility of 0.09 cm2 V−1 s−1 at a deposition temperature of 70 °C in ambient air, which is higher than the electron mobility of 0.058 cm2 V−1 s−1, obtained for PyDI-BOCF3. In contrast, PyDI-BOCF3 exhibits better thermal stability of mobility, which was maintained at ∼0.056 cm2 V−1 s−1 after increasing the deposition temperature from room temperature (RT) to 70 °C. More importantly, it is worth mentioning that the wide energy gaps of PyDI-BOCF3 and PyDI-BSCF3 lead to excellent photostability in OFETs at illumination conditions and optical transparency in the visible range even better than that of DPh-BTBT thin films on transparent glass and flexible PET substrates.

Device integration is among the current research trends in the area of organic electronics and the development of multifunctional materials is crucial to accelerate the progress of integrated devices, such as organic light-emitting transistors (OLET), organic field-effect optical waveguides (OFEW) and organic electrofluorochromic (OEFC) devices. Herein, two multifunctional materials with different side chains, 2-(4-octyloxyphenyl)anthracene (AntPh-OC8) and 2-(4-octylphenyl)anthracene (AntPh-C8), based on the concept of combining liquid crystal (LC) materials featuring facile processability, highly ordered alignment and effective charge transport and an anthracene conjugated core with strong fluorescence, are designed and successfully synthesized. The photoluminescence quantum yield (PLQY) of AntPh-OC8 and AntPh-C8 is determined to be 40.9% and 37.6%, respectively, which approaches nearly 2-fold that of 2-phenylanthracene (AntPh). Organic light-emitting diodes (OLED) based on AntPh-OC8 confirmed its solid-state blue emission with a current efficiency (CE) of 1.82 cd A−1, whereas the corresponding organic field-effect transistors (OFET) demonstrated the highest hole mobility of up to 2.59 cm2 V−1 s−1. Organic phototransistors (OPT) comprising AntPh-OC8 and AntPh-C8 revealed efficient photoresponsive characteristics of these newly developed materials. These demonstrations indicate the widespread potential of our newly developed materials for applications in multifunctional integrated devices. Moreover, these results indicate the encouraging role of side-chain engineering in the improvement of charge transport and fluorescence characteristics of anthracene derivatives.

The aromatic substituents such as phenyl and thienyl have a direct impact on the structure-property relationship of conjugated semiconducting molecules and thus play a significant role in determining the performance of organic thin film transistors (OTFTs). To design a molecule with good charge transport properties, it is essential to understand the charge transfer process. Herein, through the study of two groups of classical OTFT materials with different substituents, we demonstrate the fundamental reasons for the contrasting carrier mobilities between the materials in each group by means of DFT calculations. The results from our theoretical analysis on the two groups of molecules provide very good estimates of their charge transfer properties and the numerical trend from our calculation is consistent with that from the corresponding experimental results. We reveal in detail the impacts of the subtle geometric differences caused by different substituents from two aspects including (i) the significant influence of steric hindrance on reorganization energy and (ii) the overlap of the adjacent molecular orbitals (MOs) on electron coupling. Overall, our systematic investigation into the charge transfer mechanism and geometry effects allows us to employ a reliable theoretical methodology for the prediction of the material performance, which is crucial for the design of high performance OTFT materials.

Small molecular organic electrochromic materials have gradually attracted the attention from academia. Although ester organic electrochromic materials show unique advantages such as significant color change, wide color adjustment range and low cost, their electrochromic mechanisms are still unclear, keeping their driving voltage and stability issues unsolved. In this article, the absorption spectra of phthalate derivatives under different conditions are calculated with time-dependent density functional theory to understand the influences on the electrochromic properties by the electronic and steric effects. By the increased conjugation and reduced steric hindrance, carbonyl linking group is found capable to enhance the absorption in the visible region and exhibit low driving voltages. Further, a new electrochromic compound is designed to improve the luminous effect and lower the driving voltage.

Phosphorescent organic light-emitting diodes (PhOLEDs) have manifested enormous potential for display and lighting applications because of their high internal and external quantum efficiencies, nevertheless, severe efficiency roll-off at high luminance remains a major bottleneck in their large-scale commercialization. Herein, two new bipolar host compounds, DCbz-Ph-Bz and DDPA-Ph-Bz, based on carbazole/diphenylamine as the donor and benzimidazole as the acceptor, are successfully obtained. By employing these materials as hosts, extremely low efficiency roll-off PhOLEDs without sacrificing the efficiency are realized. Especially, green PhOLED based on DDPA-Ph-Bz as the host and GD001 as the dopant demonstrated a low turn-on voltage of 2.6 V, a peak current efficiency (CE) of 62.2 cd/A and a maximum luminance of 39,370 cd/m2. Importantly, our green device exhibited a very low efficiency roll-off as the peak external quantum efficiency (EQE) of 18.3% at 1000 cd/m2 was still retained at 17.6% even at a high luminance of 10,000 cd/m2. Likewise, red PhOLED with DCbz-Ph-Bz as the host and RD001 as the dopant displayed a high maximum EQE of 20.1% and a CE of 24.5 cd/A. High efficiency with low efficiency roll-off in our devices reveals the potential of bipolar molecules as excellent hosts to achieve high-performance PhOLEDs.

In this work, a series of novel iridium (III) cyclometallated complexes BF–Ir1, BF–Ir2 and BF–Ir3 is developed by introducing a dibenzofuran moiety into the main ligand. The photophysical, thermal, and electroluminescent properties of these iridium (III) complexes are systematically investigated. Notably, the phosphorescent organic light-emitting diodes (PhOLEDs) with BF–Ir1, BF–Ir2 and BF–Ir3 as the green emitters displayed the maximum EQEs of 15.1%, 23.7% and 21.5%, respectively. In addition, an impressively high PE up to 96.8 l m W−1 is achieved in the device based on BF–Ir3. When the luminance reached 1000 and 10000 cd m−2, the corresponding EQE values of BF–Ir3-based PhOLEDs could be maintained at 20.7% and 18.5%. These results clearly demonstrate that dibenzofuran-based iridium (III) complexes have great potential for their application as green emitters in PhOLEDs to realize both high EQE and PE as well as low efficiency roll-off.