Highly efficient thermally activated delayed fluorescent (TADF) emitters, 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (oBFCzTrz), 5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (mBFCzTrz), and 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (pBFCzTrz), were synthesized to study the effects of ortho-, meta-, and para- linkages between donor and acceptor moieties. oBFCzTrz having ortho- linked donor and acceptor moieties showed smaller singlet-triplet energy gap, shorter excited state lifetime, and higher photoluminescence quantum yield than mBFCzTrz and pBFCzTrz which are interconnected by meta- and para- positions. The TADF device using oBFCzTrz as a blue emitter exhibited high external quantum efficiency over 20%, little efficiency roll-off, and long device lifetime.

We report on the photoresponse from tetracene-based and pentacene-based thin-film transistors (TFTs) with semitransparent NiOx source/drain electrodes and SiO2∕p+-Si substrate. Both organic TFTs have been fabricated with identical channel thickness and device geometry. Compared with pentacene-based TFTs, the tetracene-TFT exhibited superior potentials as a photodetector in the visible and ultraviolet range although it showed a field mobility (μ=0.003cm2∕Vs) which is two orders of magnitude lower than that of the pentacene-based TFT (μ=∼0.3cm2∕Vs). The tetracene-TFT displayed a high photo-to-dark current ratio (Iph∕Idark) of 3×103, while that of the pentacene-TFT was only ∼10.

No abstract

Organic thin-film transistors (OTFTs) have been extensively studied over the last few decades and have become prominent in the future development of organic electronics, as exemplified by drivers for flat-panel displays, low-end smart cards, and electronic identification tags. [1][2][3] Of the many OTFTs, pentacene-based ones have attracted most attention, since pentacene-based TFTs often exhibit a reasonably high field-effect mobility of more than 1 cm 2 V -1 s -1 , demonstrating their potential for practical applications. [4][5][6] However, conventional OTFTs, including pentacene-based ones, need more than 15 V for gating and charge-transport operation to achieve desirable characteristics. Very recently, low-voltagedriven OTFTs have been reported for more advanced applications, in which high-dielectric-constant (high-k) metal oxides (Ta 2 O 3 , TiO 2 , etc.) [7][8][9][10] are adopted as gate insulators, or ultrathin gate dielectrics are used, such as self-assembled monolayers (SAMs) [11,12] and thin polymers. [13,14] Conventional high-k inorganic gate dielectric films are generally thick (typically more than ca. 100 nm) to avoid serious gate leakage current [12] and are not suitable for direct growth of an organic semiconductor channel owing to their highly hydrophilic surfaces, which are less compatible with the growth of organic crystals, probably undergoing undesirable interface interactions with organic materials. On the other hand, ultrathin organic gate dielectrics with high resultant capacitance possess good surface conditions (more hydrophobic and smoother surface) for the accommodation of an organic semiconductor channel but are still problematic due to their structural imperfections, including pinholes generated during deposition processes. [9,13,14] One way to circumvent the aforementioned drawbacks of inorganic high-k and ultrathin organic dielectrics is to stack an organic layer on a high-k inorganic film, hence selectively combining the advantages of the two gate materials.In the present Communication, we report on the fabrication and characterization of semitransparent pentacene-based TFTs with thin poly(4-vinylphenol) (PVP)/high-k yttrium oxide (YO x ) sandwich gate dielectrics, and alternatively with thermally evaporated semitransparent NiO . We also demonstrate resistance-load inverters operating below -5 V with a load resistance (R L ) of 22 MX connected to our pentacene TFTs. These inverters exhibited a sizeable voltage gain of ca. 3.0 with hysteresis on the order of 0.5 V. Figure 1a and b show, respectively, the schematic cross-sectional and photographic plan views of our pentacene TFTs, placed on the emblem of our institute. Although the S/D electrode regions appear darker than the pentacene channel or dielectric layer regions, we can still identify the emblem features printed on the paper. Our 100 nm thick NiO x electrode exhibited a transmittance of 30-40 % in the visible range but quite a low sheet resistance of ca. 100 X/& when it was deposited on Corning 7059 glass. It is highly proba...

The design and synthesis of aggregation-induced emission (AIE) luminogens have attracted rapidly growing interest owing to the fundamental significance and diverse applications in mechanosensors, optical recording, security papers, and optoelectronic devices. In this contribution we report design and synthesis of four phenanthroimidazoles 3a–3d and explored their mechanochromic and electroluminescence properties. The phenanthroimidazoles 3a–3d were synthesized by Suzuki coupling reaction of iodophenathroimidazoles 2a–2d having different end groups (H, CH3, CF3, and CN) with 4-(1,2,2-triphenylvinyl)­phenylboronic acid pinacol ester in good yields. The single crystal X-ray structures of 2b, 2c, 3a, and 3d are reported and show that the multiple phenyl rings in the TPE unit adopt nonplanar orientation. Their photophysical, aggregation induced emission (AIE), mechanochromic, electrochemical, and electroluminescence properties were studied. The phenanthroimidazoles 3a–3d exhibit strong AIE. High color contrast reversible mechanochromism between blue and green color was observed for phenanthroimidazoles 3a–3d. It was found that the solid state emission and mechanochromic behavior of tetraphenylethylene substituted phenanthroimidazoles 3a–3d are functions of the end group on phenanthroimidazole. In addition to the AIE and mechnochromic behavior, 3a and 3d compounds performed well as nondoped blue emitters in the organic light-emitting diodes by affording 3.9% and 4.0% external quantum efficiency, respectively.